PLoS Med. Early Pandemic Influenza (2009 H1N1) in Ho Chi Minh City, Vietnam: A Clinical Virological and Epidemiological Analysis

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Public Library of Science
Early pandemic influenza (2009 H1N1) in Ho Chi Minh City
Press release from PLoS Medicine

Rogier van Doorn, Maciej Boni and colleagues analyze the initial H1N1 influenza outbreak in Ho Chi Minh City, Vietnam, including attempts at containment, and establishment of community transmission. To reconstruct the initial outbreak the researchers used reports from the Ministry of Health and clinical and laboratory data for people who were infected with 2009 H1N1 and isolated in hospital. Between April 27 and July 24, three-quarters of a million passengers arriving in the city on international flights were screened at the airport. 200 passengers tested positive for 2009 H1N1 as did 121 non-travelers who were identified during this period after self-reporting illness or through contact tracing. Whilst none of the patients became severely ill, two-thirds of them experienced an influenza-like illness. The average time from starting treatment to clearance of the virus was between 2.6 and 2.8 days for patients who began treatment one to four d ays after becoming ill; whilst for those who started treatment on the first day of illness, the average virus clearance time was 2.0 days. Although the data gathered in this observational study suggest that containment may have delayed establishment of the infection, the researchers were unable to prove that containment worked. Moreover, containment did not prevent eventual community establishment of H1N1 influenza infection.

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Funding: JEB, TTN, MW, TDN, DQH, TTT, LNTN, JF, and HRvD are funded by Wellcome Trust Grants (077078/Z/05/Z, www.wellcome.ac.uk). MFB is funded by UK Medical Research Council grant G0600718 (www.mrc.ac.uk). TTH, TTN, JF, and HRvD receive support from the South East Asia Infectious Disease Clinical Research Network (N01-A0-50042, www.seaicrn.org). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests: The authors have declared that no competing interests exist.

Citation: Hien TT, Boni MF, Bryant JE, Ngan TT, Wolbers M, et al. (2010) Early Pandemic Influenza (2009 H1N1) in Ho Chi Minh City, Vietnam: A Clinical Virological and Epidemiological Analysis. PLoS Med 7(5): e1000277. doi:10.1371/journal.pmed.1000277

http://www.eurekalert.org/pub_releases/2010-05/plos-epi051110.php

 

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Re: Early pandemic influenza (2009 H1N1) in Ho Chi Minh City

Re: Early pandemic influenza (2009 H1N1) in Ho Chi Minh City


Airport screening may have delayed H1N1 spread in Vietnam

Robert Roos * News Editor

May 18, 2010 (CIDRAP News) ? An analysis of the H1N1 influenza pandemic in Ho Chi Minh City, Vietnam, suggests that the government's initial policy of screening incoming travelers might have delayed the start of widespread community transmission of the virus by a few weeks.

In late April of 2009, shortly after the detection of the new virus, Vietnamese authorities began mandatory screening of arriving air travelers, including body temperature scanning and a symptom questionnaire. The virus was widespread in Ho Chi Minh City by the second half of July, according to the study, published today by the online journal PLoS Medicine.

"The containment measures seemed to delay the onset of large-scale transmission by at least 3 weeks, said corresponding author Dr. Maciej Boni of the University of Oxford, in a press release from the Wellcome Trust, one of three organizations that sponsored the study.

"This may not sound like a lot, but in a country like Vietnam this bought valuable time for the local health services, laboratories and travel authorities to understand what was happening and start logistical preparations for the pandemic response," Boni said.

The findings do not prove that the containment measures delayed the epidemic, and the authors say they are doing further research to confirm or exclude their tentative conclusion.

Vietnam launched its airport screening program on Apr 27, 2009, when the World Health Organization moved its pandemic alert to stage 4, the report says. From then until Jul 9, 630,778 passengers arrived at Ho Chi Minh City on international flights. The screening procedures intercepted 967 of these (0.15%). They were hospitalized in isolation, tested for the virus, and treated with oseltamivir if positive.

Diagnostic data were available for 450 of the 967 intercepted passengers, 200 of whom tested positive for H1N1 between Apr 27 and Jul 24. The researchers also gathered data on 169 Ho Chi Minh City residents who had not traveled but who, in the same time frame, were tested for H1N1 because of contact tracing or after presenting at city hospitals with flu-like symptoms. Of these 169 patients, 121 tested positive.

The researchers calculated that in the first 9 weeks of the pandemic, H1N1 patients spent 79% of the days when they were infectious in isolation, which suggests a two-fold or greater reduction in their infectious capability, the report says. The team assumed patients became infectious when they got sick or tested positive; they acknowledge that an infected person can become infectious before having symptoms, but they had almost no data on the presymptomatic period.

The authors say the outbreak response was more effective against travelers than nontravelers: the travelers spent 10.1% of their potentially infectious time out in the community, while the nontravelers spent 42.2% of their time at large.

The first H1N1 case in Vietnam was reported on May 31, in a student who had returned from the United States on May 26. The first case of community transmission followed on Jun 5, and two large school outbreaks surfaced in the third week of July, signaling that community transmission was well under way.

"The epidemic in [Ho Chi Minh City] was clearly not containable, a conclusion easily inferred from previous mahthematical anlyses," the report says. However, "The containment program of screening, isolating, and treating suspected cases probably had a notable impact" on the virus's spread in the period studied.

To further test this hypothesis, the authors say they are currently following a group of healthy people to assess the frequency of asymptomatic H1N1 cases. "If the asymptomatic fraction turns out to be small or negligible, control measures may have delayed sustainable community transmission," they write. "If the asymptomatic fraction is large, control measures likely had no effect."

They add that the costs and benefits of airport screening "must be evaluated in light of the relative risks of disease introduction as well as the opportunity cost of concentrating public health resources on slowing the inevitable importation of one disease," which is difficult because the costs of the containment effort are unknown.

Hien TT, Boni MF, Bryant JE, et al. Early pandemic influenza (2009 H1N1) in Ho Chi Minh City, Vietnam: a clinical virological and epidemiological analysis. PLoS Med 2010 May 18;7(5) [Full text]


http://www.cidrap.umn.edu/cidrap/content/influenza/swineflu/news/may1810vietnam.html

 

[Giuseppe]

Re: Early pandemic influenza (2009 H1N1) in Ho Chi Minh City

Re: Early pandemic influenza (2009 H1N1) in Ho Chi Minh City

[Source: PLoS, abstract and text document (LINK), Full PDF Document (LINK). Edited.]

Early Pandemic Influenza (2009 H1N1) in Ho Chi Minh City, Vietnam: A Clinical Virological and Epidemiological Analysis

Rogier van Doorn and colleagues analyze the initial outbreak, attempts at containment, and establishment of community transmission of pandemic H1N1 influenza in Ho Chi Minh City, Vietnam.

Tran Tinh Hien 1,2,3#, Maciej F. Boni 1,4,5#*, Juliet E. Bryant 1,5#, Tran Thuy Ngan 1,3#, Marcel Wolbers 1,5, Tran Dang Nguyen 1, Nguyen Thanh Truong 2, Nguyen Thi Dung 2, Do Quang Ha 1, Vo Minh Hien 1,2, Tran Tan Thanh 1, Le Nguyen Truc Nhu 1, Le Thi Tam Uyen 1,2, Pham Thi Nhien 2, Nguyen Tran Chinh 2, Nguyen Van Vinh Chau 2, Jeremy Farrar 1,3,5, H. Rogier van Doorn 1,3,5#

1 Oxford University Clinical Research Unit, Wellcome Trust Major Overseas Program, Hospital for Tropical Diseases, Ho Chi Minh City, Vietnam,
2 Hospital for Tropical Diseases, Ho Chi Minh City, Vietnam,
3 Southeast Asian Infectious Diseases Clinical Research Network (SEAICRN, Jakarta, Indonesia,
4 MRC Centre for Genomics and Global Health, University of Oxford, Oxford, United Kingdom,
5 Centre for Tropical Medicine, Nuffield Department of Clinical Medicine, University of Oxford, Centre for Clinical Vaccinology and Tropical Medicine, Oxford, United Kingdom


Abstract

Background
To date, little is known about the initial spread and response to the 2009 pandemic of novel influenza A (?2009 H1N1?) in tropical countries. Here, we analyse the early progression of the epidemic from 26 May 2009 until the establishment of community transmission in the second half of July 2009 in Ho Chi Minh City (HCMC), Vietnam. In addition, we present detailed systematic viral clearance data on 292 isolated and treated patients and the first three cases of selection of resistant virus during treatment in Vietnam.

Methods and Findings
Data sources included all available health reports from the Ministry of Health and relevant health authorities as well as clinical and laboratory data from the first confirmed cases isolated at the Hospital for Tropical Diseases in HCMC. Extensive reverse transcription (RT)-PCR diagnostics on serial samples, viral culture, neuraminidase-inhibition testing, and sequencing were performed on a subset of 2009 H1N1 confirmed cases. Virological (PCR status, shedding) and epidemiological (incidence, isolation, discharge) data were combined to reconstruct the initial outbreak and the establishment of community transmission. From 27 April to 24 July 2009, approximately 760,000 passengers who entered HCMC on international flights were screened at the airport by a body temperature scan and symptom questionnaire. Approximately 0.15% of incoming passengers were intercepted, 200 of whom tested positive for 2009 H1N1 by RT-PCR. An additional 121 out of 169 nontravelers tested positive after self-reporting or contact tracing. These 321 patients spent 79% of their PCR-positive days in isolation; 60% of PCR-positive days were spent treated and in isolation. Influenza-like illness was noted in 61% of patients and no patients experienced pneumonia or severe outcomes. Viral clearance times were similar among patient groups with differing time intervals from illness onset to treatment, with estimated median clearance times between 2.6 and 2.8 d post-treatment for illness-to-treatment intervals of 1?4 d, and 2.0 d (95% confidence interval 1.5?2.5) when treatment was started on the first day of illness.

Conclusions
The patients described here represent a cross-section of infected individuals that were identified by temperature screening and symptom questionnaires at the airport, as well as mildly symptomatic to moderately ill patients who self-reported to hospitals. Data are observational and, although they are suggestive, it is not possible to be certain whether the containment efforts delayed community transmission in Vietnam. Viral clearance data assessed by RT-PCR showed a rapid therapeutic response to oseltamivir.

Please see later in the article for the Editors' Summary

Citation: Hien TT, Boni MF, Bryant JE, Ngan TT, Wolbers M, et al. (2010) Early Pandemic Influenza (2009 H1N1) in Ho Chi Minh City, Vietnam: A Clinical Virological and Epidemiological Analysis. PLoS Med 7(5): e1000277. doi:10.1371/journal.pmed.1000277

Academic Editor: Marc Lipsitch, Harvard School of Public Health, United States of America

Received: November 4, 2009; Accepted: April 8, 2010; Published: May 18, 2010

Copyright: ? 2010 Hien et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: JEB, TTN, MW, TDN, DQH, TTT, LNTN, JF, and HRvD are funded by Wellcome Trust Grants (077078/Z/05/Z, www.wellcome.ac.uk). MFB is funded by UK Medical Research Council grant G0600718 (www.mrc.ac.uk). TTH, TTN, JF, and HRvD receive support from the South East Asia Infectious Disease Clinical Research Network (N01-A0-50042, www.seaicrn.org). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Abbreviations: CI, confidence interval; HCMC, Ho Chi Minh City; HTD, Hospital for Tropical Diseases; InfVA, influenza A; QID, quantiles from imputed data; RT, reverse transcription; swInfVA, swine influenza A

* E-mail: mboni@oucru.org
# These authors contributed equally to this work.
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