Probable limited person-to-person transmission of highly pathogenic avian influenza A (H5N1) virus in China

[Laidback Al]

The Lancet DOI:10.1016/S0140-6736(08)60493-6

Articles
Probable limited person-to-person transmission of highly pathogenic avian influenza A (H5N1) virus in China

Hua WangMD a ?, Zijian FengMD b ?, Yuelong ShuPhD c ?, Hongjie YuMD b ?, Lei ZhouMD b, Rongqiang ZuMD a, Yang HuaiMD b, Jie DongMD c, Changjun BaoMD a, Leying WenMD c, Hong WangMD d, Peng YangPhD b, Wei ZhaoMD e, Libo DongPhD c, Minghao ZhouMD a, Qiaohong LiaoMD b, Haitao YangMD a, Min WangMD c, Xiaojun LuMD f, Zhiyang ShiMD a, Wei WangMD c, Ling GuMD a, Fengcai ZhuMD a, Qun LiMD b, Weidong YinMBA g, Weizhong YangMD b, Prof Dexin LiMD c, Timothy M UyekiMD h and Prof Yu WangPhD b
?Contributed equally


Summary

Background
In December, 2007, a family cluster of two individuals infected with highly pathogenic avian influenza A (H5N1) virus was identified in Jiangsu Province, China. Field and laboratory investigations were implemented immediately by public-health authorities.

Methods
Epidemiological, clinical, and virological data were collected and analysed. Respiratory specimens from the patients were tested by reverse transcriptase (RT) PCR and by viral culture for the presence of H5N1 virus. Contacts of cases were monitored for symptoms of illness for 10 days. Any contacts who became ill had respiratory specimens collected for H5N1 testing by RT PCR. Sera were obtained from contacts for H5N1 serological testing by microneutralisation and horse red-blood-cell haemagglutinin inhibition assays.

Findings
The 24-year-old index case died, and the second case, his 52-year-old father, survived after receiving early antiviral treatment and post-vaccination plasma from a participant in an H5N1 vaccine trial. The index case's only plausible exposure to H5N1 virus was a poultry market visit 6 days before the onset of illness. The second case had substantial unprotected close exposure to his ill son. 91 contacts with close exposure to one or both cases without adequate protective equipment provided consent for serological investigation. Of these individuals, 78 (86%) received oseltamivir chemoprophylaxis and two had mild illness. Both ill contacts tested negative for H5N1 by RT PCR. All 91 close contacts tested negative for H5N1 antibodies. H5N1 viruses isolated from the two cases were genetically identical except for one non-synonymous nucleotide substitution.

Interpretation
Limited, non-sustained person-to-person transmission of H5N1 virus probably occurred in this family cluster.

Funding
Chinese Ministry of Science and Technology; US National Institute of Allergy and Infectious Diseases, National Institutes of Health; China-US Collaborative Program on Emerging and Re-emerging Infectious Diseases.

Affiliations
a. Jiangsu Provincial Centre for Disease Control and Prevention, Nanjing, China
b. Office for Disease Control and Emergency Response, Chinese Centre for Disease Control and Prevention (China CDC), Beijing, China
c. State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Viral Disease Control and Prevention, China CDC, Beijing, China
d. Jiangsu Provincial People's Hospital, Nanjing, China
e. Nanjing Secondary People's Hospital, Nanjing, China
f. Najing Centre for Disease Control and Prevention, Nanjing, China
g. Sinovac Biotech Co, Beijing, China
h. Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA

Correspondence to: Prof Yu Wang, Chinese Center for Disease Control and Prevention, 27 Nanwei Road, Beijing, 100050, China

http://www.thelancet.com/journals/lancet/article/PIIS0140673608604936/abstract?isEOP=true

credits to Shiloh

[HenryN]

Re: Chinese son likely gave bird flu to father: report

Interestingly, today, all my feeds heads with probable 2h2 Chinese event and NO ONE talks about Indonesia (or Pakistan!). Is it a breakthrough news? I think that most of cases of 2h2 are overlooked in the media, at least in recent weeks or months. Since 1997, H5N1 tends to cluster into familiar group and this news - a part for its renowned review origin - is not unexpected at all.
If a more transmissible viral strain was emerged in souther China - densely populated - at this point there would be hundreds of thousands of cases, or millions.
Calm down, press!
China is a hot spot these days, Olympic torch permits.

doi:10.1016/S0140-6736(08)60493-6
Copyright ? 2008 Elsevier Ltd All rights reserved.


Fast track ? Articles

Probable limited person-to-person transmission of highly pathogenic avian influenza A (H5N1) virus in China

Hua Wang MD<SUP>a</SUP><SUP>, </SUP><SUP>?</SUP>, Zijian Feng MD<SUP>b</SUP><SUP>, </SUP><SUP>?</SUP>, Yuelong Shu PhD<SUP>c</SUP><SUP>, </SUP><SUP>?</SUP>, Hongjie Yu MD<SUP>b</SUP><SUP>, </SUP><SUP>?</SUP>, Lei Zhou MD<SUP>b</SUP>, Rongqiang Zu MD<SUP>a</SUP>, Yang Huai MD<SUP>b</SUP>, Jie Dong MD<SUP>c</SUP>, Changjun Bao MD<SUP>a</SUP>, Leying Wen MD<SUP>c</SUP>, Hong Wang MD<SUP>d</SUP>, Peng Yang PhD<SUP>b</SUP>, Wei Zhao MD<SUP>e</SUP>, Libo Dong PhD<SUP>c</SUP>, Minghao Zhou MD<SUP>a</SUP>, Qiaohong Liao MD<SUP>b</SUP>, Haitao Yang MD<SUP>a</SUP>, Min Wang MD<SUP>c</SUP>, Xiaojun Lu MD<SUP>f</SUP>, Zhiyang Shi MD<SUP>a</SUP>, Wei Wang MD<SUP>c</SUP>, Ling Gu MD<SUP>a</SUP>, Fengcai Zhu MD<SUP>a</SUP>, Qun Li MD<SUP>b</SUP>, Weidong Yin MBA<SUP>g</SUP>, Weizhong Yang MD<SUP>b</SUP>, Prof Dexin Li MD<SUP>c</SUP>, Timothy M Uyeki MD<SUP>h</SUP> and Prof Yu Wang PhD<SUP>b</SUP><SUP>, </SUP><SUP></SUP><SUP>, </SUP><SUP></SUP>
<SUP>a</SUP>Jiangsu Provincial Centre for Disease Control and Prevention, Nanjing, China
<SUP>b</SUP>Office for Disease Control and Emergency Response, Chinese Centre for Disease Control and Prevention (China CDC), Beijing, China
<SUP>c</SUP>State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Viral Disease Control and Prevention, China CDC, Beijing, China
<SUP>d</SUP>Jiangsu Provincial People's Hospital, Nanjing, China
<SUP>e</SUP>Nanjing Secondary People's Hospital, Nanjing, China
<SUP>f</SUP>Najing Centre for Disease Control and Prevention, Nanjing, China
<SUP>g</SUP>Sinovac Biotech Co, Beijing, China
<SUP>h</SUP>Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA

Available online 7 April 2008.

<TABLE class=refersTable cellSpacing=0 cellPadding=0><TBODY><TR><TD class=refersLeftColumn noWrap>Refers to:</TD><TD></TD><TD>Person-to-person transmission of influenza A (H5N1)
The Lancet, In Press, Corrected Proof, Available online 7 April 2008
Nguyen Tran Hien, Jeremy Farrar and Peter Horby
SummaryPlus | Full Text + Links | PDF (39 K) </TD></TR><TR class=refersDivider><TD colSpan=3></TD></TR><TR><TD class=refersLeftColumn noWrap>Referred to by:</TD><TD></TD><TD>Person-to-person transmission of influenza A (H5N1)
The Lancet, In Press, Corrected Proof, Available online 7 April 2008
Nguyen Tran Hien, Jeremy Farrar and Peter Horby
SummaryPlus | Full Text + Links | PDF (39 K) </TD></TR><TR class=refersDivider><TD colSpan=3></TD></TR></TBODY></TABLE>

Summary

Background


In December, 2007, a family cluster of two individuals infected with highly pathogenic avian influenza A (H5N1) virus was identified in Jiangsu Province, China. Field and laboratory investigations were implemented immediately by public-health authorities. Methods


Epidemiological, clinical, and virological data were collected and analysed. Respiratory specimens from the patients were tested by reverse transcriptase (RT) PCR and by viral culture for the presence of H5N1 virus. Contacts of cases were monitored for symptoms of illness for 10 days. Any contacts who became ill had respiratory specimens collected for H5N1 testing by RT PCR. Sera were obtained from contacts for H5N1 serological testing by microneutralisation and horse red-blood-cell haemagglutinin inhibition assays. Findings


The 24-year-old index case died, and the second case, his 52-year-old father, survived after receiving early antiviral treatment and post-vaccination plasma from a participant in an H5N1 vaccine trial. The index case's only plausible exposure to H5N1 virus was a poultry market visit 6 days before the onset of illness. The second case had substantial unprotected close exposure to his ill son. 91 contacts with close exposure to one or both cases without adequate protective equipment provided consent for serological investigation. Of these individuals, 78 (86%) received oseltamivir chemoprophylaxis and two had mild illness. Both ill contacts tested negative for H5N1 by RT PCR. All 91 close contacts tested negative for H5N1 antibodies. H5N1 viruses isolated from the two cases were genetically identical except for one non-synonymous nucleotide substitution. Interpretation


Limited, non-sustained person-to-person transmission of H5N1 virus probably occurred in this family cluster. Funding

Chinese Ministry of Science and Technology; US National Institute of Allergy and Infectious Diseases, National Institutes of Health; China-US Collaborative Program on Emerging and Re-emerging Infectious Diseases.



Article Outline

<DL><DT>Introduction <DT>Methods <DL><DT>Patients and procedures <DT>Role of the funding source</DT></DL><DT>Results <DT>Discussion <DT>Acknowledgements <DT>References</DT></DL>



Introduction


As of April 2, 2008, 376 cases of infection with highly pathogenic avian influenza A (H5N1) virus, with 238 deaths, had been reported from 14 countries since November, 2003.<SUP>1</SUP> Although most cases have been sporadic, about 25% have occurred in clusters of two or more epidemiologically linked people.<SUP>[2]</SUP><SUP> and </SUP><SUP>[3]</SUP> Clusters occurred in 1997<SUP>4</SUP> and 2003<SUP>5</SUP> in Hong Kong (special administrative region [SAR] of China), and during 2004?07 in Indonesia,<SUP>[6]</SUP><SUP>, </SUP><SUP>[7]</SUP><SUP> and </SUP><SUP>[8]</SUP> Turkey,<SUP>9</SUP> Azerbaijan,<SUP>10</SUP> Vietnam,<SUP>11</SUP> and Thailand.<SUP>[11]</SUP><SUP> and </SUP><SUP>[12]</SUP> Limited person-to-person transmission of the virus has been strongly suggested in the largest cluster in Indonesia<SUP>6</SUP> and in Thailand.<SUP>12</SUP> Previous cluster investigations did not adequately assess whether person-to-person transmission had occurred among exposed contacts. Illness surveillance combined with seroepidemiological investigations in exposed contacts allows a comprehensive assessment of H5N1 virus transmission.
In December, 2007, two cases of infection with H5N1 virus in one family were identified within a week in Nanjing, Jiangsu Province, China. Field and laboratory investigations were implemented immediately by public-health authorities. We report the epidemiological, clinical, and virological findings of this family cluster of confirmed H5N1 cases, including assessment of potential spread to exposed contacts. Methods

Patients and procedures


Epidemiological and clinical data were collected through interviews and review of medical records. Investigation staff interviewed case two and relatives of both cases to verify reported exposure histories during the 2 weeks before the onset of symptoms, to validate timelines of events, and to identify close contacts. We were unable to interview the index case (case one) because he was severely ill at the time of diagnosis and died on the next day. Households and places known to have been visited by the cases in the 2 weeks before the onset of illness were investigated to assess poultry and environmental exposures.
Respiratory and stool specimens were collected from the two patients during hospitalisation and placed in sterile viral transport medium for H5N1 testing.<SUP>13</SUP>
RNA was extracted from specimens with the RNeasy mini kit (Qiagen, Valencia, CA, USA) as per the manufacturer's protocol and tested by conventional reverse transcriptase (RT) PCR as recommended<SUP>14</SUP> and by real-time RT PCR with H5N1-specific primers and probes.<SUP>15</SUP> These assays were done in biosafety level (BSL) 2 facilities at Jiangsu Centre for Disease Control and Prevention (CDC), Nanjing, China, and the National Influenza Centre of the Chinese CDC (China CDC) in Beijing. Respiratory specimens were inoculated in amniotic cavities of pathogen-free embryonated chicken eggs for viral isolation<SUP>16</SUP> in enhanced BSL 3 facilities at the National Influenza Centre.
Full genomic sequencing was done on extracted viral RNA. cDNA synthesis and PCR amplification of the coding region of the eight gene segments were done with a one-step RT PCR kit (Qiagen) with gene specific primers (available on request from the authors). The PCR products were purified with the Qiagen QIAquick gel extraction kit and used as templates for nucleotide sequencing. Sequencing reactions were done with the ABI BigDye terminator sequencing kit with reaction products resolved on an ABI 3730XL DNA sequencer (Applied Biosystems, Foster City, CA, USA). Nucleotide sequences were analysed with the DNASTAR package (Lasergene, Madison, WI, USA). Phylogenetic analysis was done by neighbour-joining method with MEGA version 4. The nucleotide sequences obtained from this study are available from GenBank (accession number EU434686-EU434701).
Close contacts were placed under daily surveillance?by telephone or in person?for fever and respiratory symptoms for 10 days after their last exposure to a patient infected with H5N1 virus. Close contacts were defined as individuals known to have been within 1 m, or had contact with respiratory secretions or faecal material, of a patient with H5N1 any time from the day before the onset of illness to when the index case died or during the period that case two was hospitalised. Chemoprophylaxis with oseltamivir (75 mg orally once a day for 7 days) was recommended and distributed to contacts.
Following written informed consent, a structured questionnaire was used to gather demographic information and data on use of personal protective equipment, oseltamivir chemoprophylaxis, illness symptoms, and potential H5N1 risk factors (eg, poultry contact, visiting poultry markets, contact with individuals with febrile respiratory symptoms) during the 2 weeks before the last exposure to patients with H5N1.
Respiratory specimens were gathered from close contacts with febrile respiratory illness during the 10-day observation period for H5N1 testing. Contacts were asked to have acute and convalescent sera (≤1 week, and ≥3?4 weeks after the last exposure to a patient with H5N1, respectively) collected for H5N1 serological testing.
H5N1 serological testing was done by microneutralisation assay in a BSL 3 enhanced laboratory at the National Influenza Centre,<SUP>17</SUP> and modified horse red-blood-cell hamagglutinin inhibition assay in BSL 2 conditions at the National Influenza Centre.<SUP>18</SUP> Antigens for the assays were produced from the index case's virus isolate. Sera were tested in duplicate by two separate microneutralisation assays done on different days. An individual was deemed to be seropositive for H5N1 antibody if H5N1 neutralising antibody titres of 1:80 or greater were detected for single serum, or four-fold or greater rises for paired sera, and confirmed by horse red-blood-cell haemagglutinin inhibition assay.<SUP>[14]</SUP><SUP> and </SUP><SUP>[19]</SUP>
Data collection for H5N1 cases was determined by the Chinese Ministry of Health to be part of a continuing public-health outbreak investigation and exempt from institutional review board assessment. Case two granted permission for data collection on him and his son (case one) for research purposes. The protocol for collection of epidemiological data and serological testing of close contacts was approved by the China CDC institutional review board. Written, signed, informed consent was obtained from 91 adult contacts to participate in the study. Role of the funding source


The study sponsors had no role in the design or conduct of the study, or in the collection, analysis, or interpretation of the data. Hongjie Yu had full access to all data included in the study and is responsible for the integrity of the data and accuracy of data analyses. Yu Wang made the final decision to submit the manuscript for publication. Results


The index case, a 24-year-old male salesman, was well until August, 2007, when he experienced transient chills and sweats once or twice a month. On Nov 24, he developed fever (38?8?C), malaise, and chills, and was treated with oral antibiotics as an outpatient the next day. On Nov 27, he was hospitalised with persistent fever, chills, headache, myalgia, sore throat, cough, and sputum production. On admission, the patient had lymphopenia, moderate thrombocytopenia, and left-lower-lobe pneumonia (table 1). A blood culture taken on Nov 28 yielded Salmonella choleraesuis; he was thus treated for bacterial infection. The patient developed progressive dyspnoea, copious frothy sputum production, watery diarrhoea, and pneumonia. Despite administration of broad-spectrum antibiotics, corticosteroids, and mechanical ventilation, the patient died of acute respiratory distress syndrome, disseminated intravascular coagulation, and multiorgan failure on the fifth day in hospital. An endotracheal aspirate obtained on the fifth day of hospitalisation, just before death, was positive for H5N1 by RT PCR and H5N1 virus was isolated.

Table 1.
Clinical features of the two cases <TABLE cellSpacing=0 cellPadding=6 rules=groups border=1 frame=hsides><COLGROUP span=3> <COLGROUP><COL><COL><COL><THEAD><TR><TH vAlign=center align=left></TH><TH vAlign=center align=left>Index case</TH><TH vAlign=center align=left>Case two</TH></TR></THEAD><TBODY><TR><TD class=nowrap vAlign=center align=left headers=col1 colSpan=3>General</TD></TR><TR><TD class=nowrap vAlign=center align=left>Age (years) and sex</TD><TD class=nowrap vAlign=center align=left>24, male</TD><TD class=nowrap vAlign=center align=left>52, male</TD></TR><TR><TD class=nowrap vAlign=center align=left>Temperature (?C)<SUP>*</SUP></TD><TD class=nowrap vAlign=center align=left>40?1 (40?4)</TD><TD class=nowrap vAlign=center align=left>38?9 (40?0)</TD></TR><TR><TD class=nowrap vAlign=center align=left headers=col1 colSpan=3>Blood counts<SUP>*</SUP></TD></TR><TR><TD class=nowrap vAlign=center align=left>White blood cells (?10<SUP>9</SUP> per L)</TD><TD class=nowrap vAlign=center align=left>7?1 (0?7)</TD><TD class=nowrap vAlign=center align=left>6?7 (4?0)</TD></TR><TR><TD class=nowrap vAlign=center align=left>Lymphocytes (?10<SUP>9</SUP> per L)</TD><TD class=nowrap vAlign=center align=left>0?49 (0?12)</TD><TD class=nowrap vAlign=center align=left>1?06 (0?5)</TD></TR><TR><TD class=nowrap vAlign=center align=left>Platelets (?10<SUP>9</SUP> per L)</TD><TD class=nowrap vAlign=center align=left>88 (37)</TD><TD class=nowrap vAlign=center align=left>99 (54)</TD></TR><TR><TD class=nowrap vAlign=center align=left headers=col1 colSpan=3>Serum biochemistry<SUP>*</SUP></TD></TR><TR><TD class=nowrap vAlign=center align=left>Alanine aminotransferase (U/L)</TD><TD class=nowrap vAlign=center align=left>17?3 (107?0)</TD><TD class=nowrap vAlign=center align=left>30?7 (110?4)</TD></TR><TR><TD class=nowrap vAlign=center align=left>Aspartate aminotransferase (U/L)</TD><TD class=nowrap vAlign=center align=left>43?8 (374?0)</TD><TD class=nowrap vAlign=center align=left>61?5 (84?7)</TD></TR><TR><TD class=nowrap vAlign=center align=left>Albumin (U/L)</TD><TD class=nowrap vAlign=center align=left>36?8 (34?7)</TD><TD class=nowrap vAlign=center align=left>37?7 (37?7)</TD></TR><TR><TD class=nowrap vAlign=center align=left>Creatinine (U/L)</TD><TD class=nowrap vAlign=center align=left>96?8 (367?1)</TD><TD class=nowrap vAlign=center align=left>98 (98)</TD></TR><TR><TD class=nowrap vAlign=center align=left>Creatine kinase (U/L)</TD><TD class=nowrap vAlign=center align=left>85 (341)</TD><TD class=nowrap vAlign=center align=left>138 (138)</TD></TR><TR><TD class=nowrap vAlign=center align=left>Lactate dehydrogenase (U/L)</TD><TD class=nowrap vAlign=center align=left>328 (3036)</TD><TD class=nowrap vAlign=center align=left>548 (548)</TD></TR><TR><TD class=nowrap vAlign=center align=left headers=col1 colSpan=3>Coagulation<SUP>*</SUP></TD></TR><TR><TD class=nowrap vAlign=center align=left>Prothrombin time (seconds)</TD><TD class=nowrap vAlign=center align=left>16?6 (16?6)</TD><TD class=nowrap vAlign=center align=left>11?7 (10?06)</TD></TR><TR><TD class=nowrap vAlign=center align=left>Activated partial thromboplastin time (seconds)</TD><TD class=nowrap vAlign=center align=left>87?2 (180?1)</TD><TD class=nowrap vAlign=center align=left>39 (39?0)</TD></TR><TR><TD class=nowrap vAlign=center align=left>Fibrinogen (g/L)</TD><TD class=nowrap vAlign=center align=left>2?01 (3?28)</TD><TD class=nowrap vAlign=center align=left>4?4 (4?02)</TD></TR><TR><TD class=nowrap vAlign=center align=left headers=col1 colSpan=3>Arterial blood<SUP>*</SUP></TD></TR><TR><TD class=nowrap vAlign=center align=left>PaCO<SUB>2</SUB> (mm Hg)</TD><TD class=nowrap vAlign=center align=left>23?3 (36)</TD><TD class=nowrap vAlign=center align=left>27 (28)</TD></TR><TR><TD class=nowrap vAlign=center align=left>PaO<SUB>2</SUB> (mm Hg)</TD><TD class=nowrap vAlign=center align=left>42 (44)</TD><TD class=nowrap vAlign=center align=left>59 (66)</TD></TR><TR><TD class=nowrap vAlign=center align=left>Bicarbonate (mEq/L)</TD><TD class=nowrap vAlign=center align=left>14?6 (26?4)</TD><TD class=nowrap vAlign=center align=left>20?1 (19?5)</TD></TR><TR><TD class=nowrap vAlign=center align=left>Alveolar-arterial oxygen gradient (mm Hg)</TD><TD class=nowrap vAlign=center align=left>79 (83)</TD><TD class=nowrap vAlign=center align=left>92 (94)</TD></TR><TR><TD class=nowrap vAlign=center align=left headers=col1 colSpan=3>Other</TD></TR><TR><TD class=nowrap vAlign=center align=left>Chest radiography</TD><TD class=nowrap vAlign=center align=left>Left lower-lobe infiltrate</TD><TD class=nowrap vAlign=center align=left>Right upper, bilateral lower-lobe infiltrates</TD></TR><TR><TD class=nowrap vAlign=center align=left>Gastrointestinal symptoms</TD><TD class=nowrap vAlign=center align=left>More than five episodes of watery diarrhoea without blood or mucus on the night of day 4 and ≥15 episodes on day 5</TD><TD class=nowrap vAlign=center align=left>Two episodes of watery diarrhoea without blood or mucus on day 3</TD></TR><TR><TD class=nowrap vAlign=center align=left>Complications</TD><TD class=nowrap vAlign=center align=left>Acute respiratory distress syndrome, respiratory failure, cardiac failure, disseminated intravenous coagulation, liver function impairment, renal dysfunction</TD><TD class=nowrap vAlign=center align=left>Respiratory failure, liver dysfunction</TD></TR><TR><TD class=nowrap vAlign=center align=left headers=col1 colSpan=3>Treatment</TD></TR><TR><TD class=nowrap vAlign=center align=left>Mechanical ventilation</TD><TD class=nowrap vAlign=center align=left>Intubation</TD><TD class=nowrap vAlign=center align=left>Mask positive pressure ventilation</TD></TR><TR><TD class=nowrap vAlign=center align=left>Corticosteroids</TD><TD class=nowrap vAlign=center align=left>Methylprednisolone 40 mg intravenously twice daily on days 6?9</TD><TD class=nowrap vAlign=center align=left>Methylprednisolone 40 mg intravenously twice daily on days 3?8</TD></TR><TR><TD class=nowrap vAlign=center align=left>Rimantadine</TD><TD class=nowrap vAlign=center align=left>No</TD><TD class=nowrap vAlign=center align=left>100 mg orally twice daily on days 3?7</TD></TR><TR><TD class=nowrap vAlign=center align=left>Oseltamivir</TD><TD class=nowrap vAlign=center align=left>No</TD><TD class=nowrap vAlign=center align=left>75 mg orally daily on day 1 of illness, 150 mg orally twice daily on days 2?6</TD></TR><TR><TD class=nowrap vAlign=center align=left>Passive immunotherapy</TD><TD class=nowrap vAlign=center align=left>No</TD><TD class=nowrap vAlign=center align=left>2?200 mL transfusion of post-vaccination plasma on day 5</TD></TR><TR><TD class=nowrap vAlign=center align=left>Days from onset to death or discharge</TD><TD class=nowrap vAlign=center align=left>8, died</TD><TD class=nowrap vAlign=center align=left>23, discharge</TD></TR></TBODY></TABLE><SUP>*</SUP> Data are measurement at admission (peak or nadir measurement during hospitalisation).

Case two (the index patient's father), a 52-year-old retired engineer with hypertension, developed fever (38?1?C), chills, and cough on Dec 3. That night he took one dose of oseltamivir (75 mg orally) that had been distributed for chemoprophylaxis to contacts of the index case. The next morning, he was hospitalised with fever, mild thrombocytopenia, and bilateral pneumonia, and treated with levofloxacin, corticosteroids, and oseltamivir (150 mg orally twice daily for 5 days; table 1). Rimantadine (100 mg orally twice daily for 5 days) was started on day 3 of his illness. His respiratory status worsened, requiring positive pressure ventilation. On Dec 7, he received two 200 mL transfusions of plasma at 0100 h and 0500 h from a 30-year-old woman who had received two doses of inactivated whole-virion H5N1 vaccine (days 0 and 28) in a phase I clinical trial.<SUP>20</SUP> Plasma obtained 280 days after the second vaccine dose was negative for hepatitis B virus, hepatitis C virus, and HIV, and was heat-inactivated at 56?C for 10 h (neutralising antibody titres 1:40 against the clade 1 vaccine strain A/Vietnam/1194/2004-RG and 1:20 against case two's virus strain A/Jiangsu/2/2007). The patient's fever resolved that night. A chest radiograph on Dec 12 (day 10) showed improvement in the right upper and bilateral lower lobes (figure 1). H5N1 virus was isolated from a throat swab collected on day 4 of the patient's illness, and H5N1 viral RNA was detected in throat and stool specimens up to 10 days after the onset of illness. The patient recovered fully and was discharged 22 days after admission.

<TABLE width="100%"><TBODY><TR><TD width="10%"></TD><TD vAlign=bottom>Display Full Size version of this image (39K)
Display High Quality version of this image (212K)</TD></TR></TBODY></TABLE>
Figure 1. Improvement of pulmonary lesions in chest radiographs from case two
(A) Bilateral lower-lobe infiltrates on day 4 of illness. (B) Reduction of pulmonary lesions in the right upper and bilateral lower lobes on day 10 of illness.

Complete genomic sequencing showed that the H5N1 viruses isolated from the index case (A/Jiangsu/1/2007) and case two (A/Jiangsu/2/2007) were identical, except for one non-synonymous nucleotide substitution in the NS gene (glutumate to glycine at aminoacid position 82) coding for the NS2 protein. All genes were entirely of avian origin and both isolates were characterised as H5N1 clade 2.3.4 viruses.<SUP>2</SUP> Sequence analyses indicated that these two isolates were highly homologous (sharing 97?2?98?9% homology in aminoacid sequences of the haemagglutinin gene) with viruses isolated from H5N1 cases in southern China. The haemagglutinin receptor-binding site was similar to that of other H5N1 viruses, and a polybasic aminoacid cleavage site (LRERRRKRG) was present. Sequencing of the M2 and neuraminidase genes of both viruses suggested susceptibility to adamantane and neuraminidase inhibitor antiviral drugs.
The index case lived with his mother in an apartment located in an urban area 10 km from his father's home, and rarely shared meals with him. No poultry were raised in the home or neighbourhood, and no live poultry were ever brought home. He had been bitten by a healthy pet dog 25 days before the onset of H5N1 illness and received four doses of rabies vaccine. He had consumed cooked poultry four times at restaurants during the 2 weeks before the onset of illness. No live poultry were present or slaughtered at these restaurants. He did not have any known direct contact with live poultry or ill individuals in the 2 weeks before the onset of illness. 6 days before the onset of illness, he visited a market to purchase vegetables and freshly killed pork with his girlfriend. She reported that the index case had not gone near the area where live poultry were sold and slaughtered in the market, 10 m from the section they had visited.
The index case's father did not raise poultry and had not brought live poultry into the home. He visited a market to purchase vegetables and bean curd 15 days and 8 days before the onset of illness. Live poultry were sold and slaughtered at this market, but the patient denied going near this area, which was 20 m from the vegetable stalls. The patient did not have any known contact with ill individuals except for his son during the 2 weeks before the onset of illness. After the index case became ill, the patient had close contact with him five times, including eating dinner together, providing care, and attending his funeral (table 2). He provided unprotected bedside hospital care for the index case between Nov 27 and 29. The longest continuous time he spent caring for his son was 20 h. During this period, the index case had high fever (40?0?C), frequent coughing, extensive sputum production, and frequent episodes of watery diarrhoea. Case two had helped to change his son's soiled clothes and bedsheets, and had cleaned the toilet that had been used to dispose of diarrhoeal stool and a spittoon that contained copious sputum. The patient did not use personal protective equipment until after H5N1 had been confirmed in the index case late on Dec 1. A summary of the patient's exposure to one another is shown in figure 2.

Table 2.
Detailed exposure of case two to the index case before the onset of illness <TABLE cellSpacing=0 cellPadding=6 rules=groups border=1 frame=hsides>


<TBODY></TBODY></TABLE>

<TABLE width="100%"><TBODY><TR><TD width="10%"></TD><TD vAlign=bottom>Display Full Size version of this image (41K)
Display High Quality version of this image (431K)</TD></TR></TBODY></TABLE>
Figure 2. Timeline of pertinent exposures and dates of onset of illness

100 close contacts of the H5N1 cases were identified and followed up daily for 10 days. Of these, 91 (91%) gave consent for collection of data, completed a questionnaire, and provided serum specimens, including nine (10%) household contacts, five (5%) social contacts, and 77 (85%) health-care workers who cared for the two cases (table 3). Eight contacts (the index patient's mother and girlfriend, four family members, one colleague of the mother, and one health-care worker) were exposed to both cases.

Table 3.
Type of exposure and sera collection of 91 close contacts <TABLE cellSpacing=0 cellPadding=6 rules=groups border=1 frame=hsides>


<TBODY></TBODY></TABLE>
Data are median (IQR) or n (%).
<SUP>*</SUP> Including direct contact (touching), preparation, cooking, and consumption of well-appearing poultry.
<SUP>?</SUP> For each of these analyses, data available for one participant only.

The median duration of exposure to at least one of the cases was 7 h (IQR 2?36). 78 (86%) of the close contacts reported taking oseltamivir chemoprophylaxis beginning on Dec 3, and some reported always wearing protective equipment, including surgical masks, N95 respirators, gloves, face shields, glasses, or gowns while caring for the two cases (table 3). No adverse effects attributed to oseltamivir chemoprophylaxis were reported.
Only two of the 100 close contacts who were followed up?the index patient's girlfriend and one doctor?developed acute respiratory symptoms during the 10-day surveillance period. The girlfriend had a temperature of 37?3?C and onset of cough 5 days after her last known exposure to the index case and 1 day after her last known exposure to the index case's father. The doctor had a temperature of 37?3?C 3 days after the last known exposure to the index case. Both ill contacts had normal chest radiographs, and throat swabs collected from them on the first day of illness were negative for H5N1 by RT PCR.
Paired acute and convalescent sera were collected from 30 (33%) close contacts (table 3), including from the index case's girlfriend. A convalescent serum specimen was collected from 61 (67%) other close contacts (table 3), including the ill doctor. All serum tested negative for H5N1 antibodies (ie, all H5N1 neutralising antibody titres <1:10) by microneutralisation and horse red-blood-cell haemagglutinin inhibition assays. Discussion


In this family cluster of confirmed cases of infection with highly pathogenic avian influenza A (H5N1) virus in mainland China, we believe that the index case transmitted H5N1 virus to his father while his father cared for him in the hospital. The index case had high fever, cough, extensive sputum production, and watery diarrhoea while his father had prolonged, direct, and close unprotected contact with him. His father did not have any known exposure to poultry or to any other ill person before the onset of his illness. Possible transmission sources include inhalation of droplets expelled by the index case through coughing or via contact with the index case's clothes that were contaminated with diarrhoeal stool and subsequent inoculation of mucous membranes or the respiratory tract. Unlike in previous reports,<SUP>[6]</SUP><SUP> and </SUP><SUP>[12]</SUP> viral isolates were available from all cases. Our epidemiological findings are supported by genetic sequencing data that indicate that both case's H5N1 viral isolates were virtually identical.
We cannot ascertain when person-to-person transmission of H5N1 virus occurred, but the most likely incubation period after the father's unprotected exposure to his severely ill son is 4?5 days (range 3?6). Transmission is unlikely to have occurred during exposure to the index case at a restaurant on the day of fever onset, since the index case had yet to start coughing, or during a final 30-min hospital visit 3 days before the father's illness started. Although the index case's respiratory tract H5N1 viral load was probably high during his hospitalisation, his father wore a surgical mask during his last visit, but did not wear protective equipment during earlier hospital exposures. We doubt that transmission occurred at the funeral of the index case, a day before the onset of the father's illness, when personal protective equipment was used.
The only potential place of exposure to H5N1 virus that we identified for the index case was a market visit 6 days before the onset of illness. Visiting a wet poultry market, where avian influenza A viruses can be maintained and amplified,<SUP>21</SUP> has been identified as a risk factor for H5N1 infection in Hong Kong SAR<SUP>22</SUP> and urban China.<SUP>23</SUP> No outbreaks of H5N1 in poultry were identified in Nanjing before or after the two human cases were detected, and no sick or dead poultry were seen at markets in Nanjing during our investigations. Only H5-vaccinated poultry were sold in the markets visited by the cases. In parallel with our investigations, 540 cloacal, faecal, and environmental specimens were collected from live poultry, wild birds, and surfaces at 23 poultry markets, restaurants (including markets and restaurants visited by both cases), and parks in Nanjing City between Dec 2 and Dec 9. All specimens tested negative by real-time RT PCR for H5N1 and by virus culture at the Jiangsu Provincial Centre for Animal Disease Control and Prevention (Yaoxing Liu, personal communication). With regard to the father, the estimated H5N1 incubation period of 3?6 days after exposure to his son is more plausible<SUP>2</SUP> than the 8 days that had passed since his last visit to the market. However, we cannot exclude completely the possibility that both cases were infected with virtually the same H5N1 viral strain through exposures to different live poultry markets located 10 km apart with different sources of poultry.
The index case is unlikely to have acquired H5N1 virus infection through consumption of cooked poultry or poultry products, including boiled duck blood. There is no epidemiological evidence to date that H5N1 viruses can be transmitted to human beings by consumption of properly cooked poultry.<SUP>24</SUP> H5N1 virus infection has been detected in the gastrointestinal tract, but whether this is the site of initial infection is currently unknown.<SUP>25</SUP> We do not believe that the index case acquired H5N1 virus infection from contact with his pet dog, although infection of dogs with H5N1 virus has been documented.<SUP>26</SUP> A serum specimen collected from the dog on Jan 7, 2008, tested negative for H5N1 neutralising antibodies (unpublished data).
The index patient's positive bacterial blood culture result on Nov 28 delayed a diagnosis of H5N1 until he deteriorated while receiving broad-spectrum antibiotics. The effect of S choleraesuis infection on susceptibility to infection with H5N1 virus?or the severity of such infection?is unknown, especially since only one colony was found on blood culture, and contamination or partial pretreatment as an outpatient cannot be ruled out. S choleraesuis causes swine paratyphoid, and occasionally infects human beings and can cause bacteraemia.<SUP>[27]</SUP><SUP> and </SUP><SUP>[28]</SUP> Transient bacteraemia could explain the occasional febrile episodes he experienced in the 3 months before his H5N1 illness, although the timing of his bacterial infection is unknown. Since this pathogen is usually acquired from pigs, this infection could indicate food or water contamination.<SUP>27</SUP> However, the index case was reported to have eaten only properly cooked meat.
We found no evidence of transmission of H5N1 virus from the cases to any other close contacts, including the index case's mother and girlfriend, both of whom had prolonged, direct, and close unprotected exposure to both patients. A convalescent serum specimen was available for more than 90% of contacts?including two who had subsequently reported illness?and all were negative for H5N1 antibodies. All 34 individuals who reported visiting a live poultry market in the 2 weeks before the onset of illness in the two cases were also negative for antibodies against the virus. In 1997, one social contact,<SUP>29</SUP> six (12%) household contacts,<SUP>29</SUP> and eight (4%) health-care workers<SUP>30</SUP> exposed to cases had H5N1 neutralising antibodies. Our findings are consistent with studies done among health-care workers exposed to H5N1 cases in Vietnam<SUP>[31]</SUP><SUP> and </SUP><SUP>[32]</SUP> and Thailand<SUP>33</SUP> during 2004.
More than 90% of H5N1 case clusters have occurred in blood-related family members.<SUP>2</SUP> Although exposures must always be assessed among non-blood-relatives, this observation suggests that research is needed into potential genetic susceptibility to H5N1 virus infection.<SUP>34</SUP> The major challenge of such a study is the small number of case clusters that have occurred in different countries, which would require close international collaborations.
Unlike the index case, who was not diagnosed with H5N1 until just before death and did not receive oseltamivir, case two received early treatment with oseltamivir and rimantadine. On the fifth day of illness, he was also given post-vaccination plasma from a participant in a clade 1 H5N1 vaccine clinical trial.<SUP>20</SUP> The plasma showed fairly low cross-reactivity with the clade 2.3.4 H5N1 virus strain isolated from this case. Although case two's treatment with post-vaccination plasma was uncontrolled, as it was when another H5N1 patient also received convalescent H5N1 plasma,<SUP>35</SUP> survival of both cases warrants research into antiviral treatment combined with passive immunotherapy for individuals infected with H5N1 virus. Corticosteroids were given to both cases here, although WHO recommends against routine corticosteroid treatment for such patients.<SUP>36</SUP>
Our investigations had several limitations. We could not elicit a complete exposure history from the index case before his death, but we interviewed his contacts, including his girlfriend, to verify his activities as much as possible. We also believe that it is difficult to trace all contacts who came within 1 m of the cases. We might have missed seroconversion in the nine contacts that remained healthy during the 10-day surveillance period, but who had declined serum collection. However, we believe that our serological findings from the other contacts, including all household and family contacts, suggest that it is unlikely that any asymptomatic or subclinical H5N1 virus infections were missed. We did not isolate any more than one H5N1 virus from either case to compare isolates during the case's clinical course. Stool specimens were not collected from the index case for H5N1 testing, but H5N1 virus has been detected or isolated from rectal swab and stool specimens from other patients infected with H5N1,<SUP>37</SUP> including the index case's father. Lastly, we were unable to assess H5N1 viral load in serial clinical specimens from case two because the quality of some of the specimens was suboptimal.
Our conclusion that limited, non-sustained person-to-person transmission of H5N1 virus probably occurred in this family cluster does not imply that H5N1 viruses have attained the ability to transmit more efficiently in human beings. A switch in receptor binding affinity has been suggested as a necessary factor,<SUP>[38]</SUP><SUP> and </SUP><SUP>[39]</SUP> but human infection with H5N1 virus that binds to receptors with α2,6-sialic acid linkages has occurred without further spread.<SUP>40</SUP> Viral characteristics required for sustained person-to-person H5N1 virus transmission remain unknown. H5N1 clusters require urgent investigation because of the possibility that a change in the epidemiology of H5N1 cases could indicate that H5N1 viruses have acquired the ability to spread more easily among people.
Contributors
Yu Wang, Hongjie Yu, Hua Wang, and Zijian Feng designed the protocol of investigation, set up the field epidemiology and clinical investigation, contacted all investigators; Hongjie Yu draft the manuscript; Dexin Li, Yuelong Shu, Jie Dong, Leying Wen, Libo Dong, Min Wang, Zhiyang Shi, and Ling Gu were responsible for virus isolation, microneutralisation, haemagglutination inhibition assay, RT PCR and real-time RT PCR testing, including the experimental design and analysis of data; Timothy Uyeki provided technical assistance for the epidemiological investigations, helped to review the data, and contributed to revising the manuscript. All other co-authors participated in collection and management of data.
Conflict of interest statement We declare that we have no conflict of interest.





Acknowledgments
We thank the local Centres for Disease Control and Prevention of Xuanwu District and Gulou District in Najing City for assistance in coordinating field investigations and provision logistics support. The views expressed in this study are those of the authors and do not represent the policy of China CDC or the US CDC. This study was supported by grants (2004BA519A17, 2004BA519A71, and 2006BAD06A02) from the Chinese Ministry of Science and Technology, the US National Institute of Allergy and Infectious Diseases, National Institutes of Health (CIPRA grant U19 AI51915), and the China-US Collaborative Program on Emerging and Re-emerging Infectious Diseases.



References


1 WHO, Cumulative number of confirmed human cases of avian influenza A/(H5N1) reported to WHO http://www.who.int/csr/disease/avian_influenza/country/cases_table_2008_04_02/en/ (accessed March 19, 2008)..
2 Writing Committee of the Second WHO Consultation on Clinical Aspects of Human Infection with Avian Influenza A (H5N1) Virus, Update on avian influenza A (H5N1) virus infection in humans, N Engl J Med 358 (2008), pp. 261?273.
3 WHO, WHO guidelines for investigation of human cases of avian influenza A http://www.who.int/csr/resources/publications/influenza/WHO_CDS_EPR_GIP_2006_4r1.pdf (accessed March 3, 2008)..
4 KY Yuen, PK Chan and M Peiris et al., Clinical features and rapid viral diagnosis of human disease associated with avian influenza A H5N1 virus, Lancet 351 (1998), pp. 467?471. SummaryPlus | Full Text + Links | PDF (174 K) | View Record in Scopus | Cited By in Scopus (380)
5 JS Peiris, WC Yu and CW Leung et al., Re-emergence of fatal human influenza A subtype H5N1 disease, Lancet 363 (2004), pp. 617?619. SummaryPlus | Full Text + Links | PDF (639 K) | View Record in Scopus | Cited By in Scopus (192)
6 WHO, Avian influenza?situation in Indonesia?update 16 http://www.who.int/csr/don/2006_05_31/en/ (accessed March 3, 2008)..
7 IN Kandun, H Wibisono and ER Sedyaningsih et al., Three Indonesian clusters of H5N1 virus infection in 2005, N Engl J Med 355 (2006), pp. 2186?2194. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (28)
8 ER Sedyaningsih, S Isfandari and V Setiawaty et al., Epidemiology of cases of H5N1 virus infection in Indonesia, July 2005?June 2006, J Infect Dis 196 (2007), pp. 522?527. View Record in Scopus | Cited By in Scopus (2)
9 AF Oner, A Bay and S Arslan et al., Avian influenza A (H5N1) infection in eastern Turkey in 2006, N Engl J Med 355 (2006), pp. 2179?2185. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (19)
10 Anon, Human avian influenza in Azerbaijan, February?March 2006, Wkly Epidemiol Rec 81 (2006), pp. 183?188.
11 S Olsen, K Ungchusak and L Sovann et al., Family clustering of avian influenza A (H5N1), Emerg Infect Dis 11 (2005), pp. 1799?1801. View Record in Scopus | Cited By in Scopus (17)
12 K Ungchusak, P Auewarakul and SF Dowell et al., Probable person-to-person transmission of avian influenza A (H5N1), N Engl J Med 352 (2005), pp. 333?340. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (260)
13 WHO, Collecting, preserving and shipping specimens for the diagnosis of avian influenza A(H5N1) virus infection. Guide for field operations www.who.int/csr/resources/publications/surveillance/WHO_CDS_EPR_ARO_2006_1/en/ (accessed March 3, 2008)..
14 WHO, Recommendations and laboratory procedures for detection of avian influenza A(H5N1) virus in specimens from suspected human cases http://www.who.int/csr/disease/avian_influenza/guidelines/labtests/en/ (accessed March 3, 2008)..
15 E Spackman, DA Senne and TJ Myers et al., Development of a real-time reverse transcriptase PCR assay for type A influenza virus and the avian H5 and H7 hemagglutinin subtypes, J Clin Microbiol 40 (2002), pp. 3256?3260. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (137)
16 WHO, WHO manual on animal influenza diagnosis and surveillance http://www.who.int/vaccine_research/diseases/influenza/WHO_manual_on_animal-diagnosis_and_surveillance_2002_5.pdf (accessed March 3, 2008)..
17 T Rowe, RA Abernathy and J Hu-Primmer et al., Detection of antibody to avian influenza A (H5N1) virus in human serum by using a combination of serologic assays, J Clin Microbiol 37 (1999), pp. 937?943. View Record in Scopus | Cited By in Scopus (93)
18 I Stepheson, JM Wood, KG Nicholson and MC Zambon, Sialic acid receptor specificity on erythrocytes affects detection of antibody to avian influenza haemagglutinin, J Med Virol 70 (2003), pp. 391?398.
19 WHO, WHO case definitions for human infections with influenza A (H5N1) virus http://www.who.int/csr/disease/avian_influenza/guidelines/case_definition2006_08_29/en/ (accessed March 3, 2008)..
20 J Lin, J Zhang and X Dong et al., Safety and immunogenicity of an inactivated adjuvanted whole-virion influenza A (H5N1) vaccine: a phase I randomised controlled trial, Lancet 368 (2006), pp. 991?997. SummaryPlus | Full Text + Links | PDF (134 K) | View Record in Scopus | Cited By in Scopus (36)
21 RG Webster, Wet markets?a continuing source of severe acute respiratory syndrome and influenza?, Lancet 363 (2004), pp. 234?236. SummaryPlus | Full Text + Links | PDF (393 K) | View Record in Scopus | Cited By in Scopus (57)
22 AW Mounts, H Kwong and HS Izurieta et al., Case-control study of risk factors for avian influenza A (H5N1) disease, Hong Kong, 1997, J Infect Dis 180 (1999), pp. 505?508. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (93)
23 H Yu, Z Feng and X Zhang et al., Human influenza A(H5N1) cases, urban areas of People's Republic of China, 2005?2006, Emerg Infect Dis 13 (2007), pp. 1061?1064. View Record in Scopus | Cited By in Scopus (1)
24 Scientific Report of the Scientific Panel on Biological Hazards, Food as a possible source of infection with highly pathogenic avian influenza viruses for humans and other mammals, Eur Food Safety Authority J 74 (2006), pp. 1?29.
25 J Gu, Z Xie and Z Gao et al., H5N1 infection of the respiratory tract and beyond: a molecular pathology study, Lancet 370 (2007), pp. 1137?1145. SummaryPlus | Full Text + Links | PDF (381 K) | View Record in Scopus | Cited By in Scopus (6)
26 T Songserm, A Amonsin and R Jam-on et al., Fatal avian influenza A H5N1 in a dog, Emerg Infect Dis 12 (2006), pp. 1744?1747. View Record in Scopus | Cited By in Scopus (15)
27 CH Chiu, LH Su and C Chu, Salmonella enterica serotype Choleraesuis: epidemiology, pathogenesis, clinical disease, and treatment, Clin Microbiol Rev 17 (2004), pp. 311?322. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (29)
28 P Chassagne, MB Perol and J Doucet et al., Is presentation of bacteremia in the elderly the same as in younger patients?, Am J Med 100 (1996), pp. 65?70. SummaryPlus | Full Text + Links | PDF (600 K) | View Record in Scopus | Cited By in Scopus (47)
29 JM Katz, W Lim and CB Bridges et al., Antibody response in individuals infected with avian influenza A (H5N1) viruses and detection of anti-H5 antibody among household and social contacts, J Infect Dis 180 (1999), pp. 1763?1770. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (92)
30 C Buxton Bridges, JM Katz and WH Seto et al., Risk of influenza A (H5N1) infection among health care workers exposed to patients with influenza A (H5N1), Hong Kong, J Infect Dis 181 (2000), pp. 344?348. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (101)
31 NT Liem and W Lim, Lack of H5N1 avian influenza transmission to hospital employees, Hanoi, 2004, Emerg Infect Dis 11 (2005), pp. 210?215.
32 C Schultsz, VC Dong and NV Chau et al., Avian influenza H5N1 and healthcare workers, Emerg Infect Dis 11 (2005), pp. 1158?1159. View Record in Scopus | Cited By in Scopus (28)
33 A Apisarnthanarak, S Erb and I Stephenson et al., Seroprevalence of anti-H5 antibody among Thai health care workers after exposure to avian influenza (H5N1) in a tertiary care center, Clin Infect Dis 40 (2005), pp. e16?e18. Full Text via CrossRef
34 VE Pitzer, SJ Olsen, CT Bergstrom, SF Dowell and M Lipsitch, Little evidence for genetic susceptibility to influenza A (H5N1) from family clustering data, Emerg Infect Dis 13 (2007), pp. 1074?1076. View Record in Scopus | Cited By in Scopus (2)
35 B Zhou, N Zhong and Y Guan, Treatment with convalescent plasma for influenza A (H5N1) Infection, N Engl J Med 357 (2007), pp. 1450?1451. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (2)
36 WHO, Clinical management of human infection with avian influenza A (H5N1) virus http://www.who.int/csr/disease/avian_influenza/guidelines/clinicalmanage07/en/index.html (accessed March 3, 2008)..
37 MD de Jong, CP Simmons and TT Thanh et al., Fatal outcome of human influenza A (H5N1) is associated with high viral load and hypercytokinemia, Nat Med 12 (2006), pp. 1203?1207. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (72)
38 J Stevens, O Blixt and TM Tumpey et al., Structure and receptor specificity of the hemagglutinin from an H5N1 influenza virus, Science 312 (2006), pp. 404?410. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (70)
39 S Yamada, Y Suzuki and T Suzuki et al., Haemagglutinin mutations responsible for the binding of H5N1 influenza A viruses to human-type receptors, Nature 444 (2006), pp. 378?382. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (48) 40 P Auewarakul, O Suptawiwat and A Kongchanagul et al., An avian influenza H5N1 virus that binds to a human-type receptor, J Virol 81 (2007), pp. 9950?9955. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (3)




<SUP></SUP>Correspondence to: Prof Yu Wang, Chinese Center for Disease Control and Prevention, 27 Nanwei Road, Beijing, 100050, China
<SUP>?</SUP> Contributed equally

[Commonground]

Re: Probable limited person-to-person transmission of highly pathogenic avian influenza A (H5N1) virus in China

A switch in receptor binding affinity has been suggested as a necessary factor,[38] and [39] but human infection with H5N1 virus that binds to receptors with α2,6-sialic acid linkages has occurred without further spread.40 Viral characteristics required for sustained person-to-person H5N1 virus transmission remain unknown.