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WER Wkly Epidemiol Rec. Update on human cases of highly pathogenic avian influenza A (H5N1) infection: 2009

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  • WER Wkly Epidemiol Rec. Update on human cases of highly pathogenic avian influenza A (H5N1) infection: 2009

    Update on human cases of highly pathogenic avian influenza A (H5N1) infection: 2009 (Wkly Epidemiol Rec., edited)

    [Source Full PDF Document: LINK. EDITED.]

    Weekly epidemiological record - Relev? ?pid?miologique hebdomadaire
    12 FEBRUARY 2010, 85th YEAR / 12 F?VRIER 2010, 85e ANN?E
    No. 7, 2010, 85, 49?56
    The Weekly Epidemiological Record (WER) serves as an essential instrument for the rapid and accurate dissemination of epidemiological information.



    Update on human cases of highly pathogenic avian influenza A (H5N1) infection: 2009

    During 2009, 73 laboratory-confirmed cases of human infection with highly pathogenic avian influenza A (H5N1) virus were reported to WHO from 5 countries. This report summarizes these cases.


    Temporal and geographical distribution

    The 73 laboratory-confirmed cases of H5N1 virus infection were reported from Cambodia (1 case), China (7), Egypt (39), Indonesia (21) and Viet Nam (5); all of these countries reported human cases of H5N1 previously. Circulation of highly pathogenic H5N1 virus in poultry is considered to be endemic in these countries, with the exception of Cambodia, where poultry outbreaks occur sporadically. As in previous years,1 an increase in cases was reported during the northern hemisphere?s winter and spring seasons (Fig. 1). Reports of outbreaks among animals also tended to increase during the same period.


    Distribution by sex and age

    In 2009, the overall ratio of male cases (n=35) to female cases (n=38) was almost even (ratio of males to females, 0.92). However, Indonesia reported twice as many cases in females as in males (ratio, 0.5). Cases ranged in age from 6 months to 57 years, with a median age of 5 years. The low median age was due primarily to the high proportion of cases occurring among children in Egypt; Egypt accounted for 53% of all cases worldwide. The age of cases in Egypt was notably younger than elsewhere, with a median age of 3 years; 80% of cases occurred in children aged <10 years.


    Outcome

    The overall case-fatality ratio (CFR) for 2009 was 44%, lower than the previous 2 years but similar to the CFR in 2005 (Table 1). CFRs varied widely among countries. Egypt reported its lowest CFR (10%) since 2003. In all countries, the CFR was lower for cases aged <10 years than for cases aged >10 years (24% versus 71%; odds ratio [OR], 7.8; 95% confidence interval [CI], 2.7?22.4). In contrast to previous years, the CFR for females in all countries was higher than for males, but the difference was not significant (50% versus 37%; OR, 1.7; 95% CI, 0.7?4.3); this pattern was not consistent among countries.


    Discussion

    With almost double the number of human cases of H5N1 reported in 2009 compared with 2008, and with continuing circulation of the virus among certain poultry populations, it is clear that H5N1 remains a concern for both animal health and public health. Although the CFR remains high, there are differences among affected countries. These data do not allow a determination of the causes of this difference to be made. Possible explanations for the disparities among countries might include differences in the type or intensity of exposure, in health-seeking behaviour, in testing or treatment practices, or even in the virulence of virus strains. The marked difference in the age distribution of cases among countries makes a direct comparison of risk factors difficult, given the relatively small total number of cases available for analysis. At present, this remains an avian virus that has not demonstrated a facility for human-to-human transmission, and human infections remain rare and sporadic. Three clusters, each involving 2 family members and without sustained human-to-human transmission, were documented in 2009.

    It is notable that all cases have occurred in countries with ongoing circulation or reintroduction of highly pathogenic avian influenza A(H5N1) viruses in poultry.

    Globally, better management of outbreaks in poultry in many countries has led to a decrease in virus circulation and a decreased risk of human exposure. However, human exposure and cases can continue to be expected whenever the virus is circulating. Efforts should be intensified to decrease both circulation in poultry and the risk of human exposure.

    Influenza viruses mutate constantly, and vigilance must be maintained. Surveillance of influenza in humans and animals should be strengthened to enable timely detection of epidemiological, clinical and virological changes.

    The rapid sharing of information globally is essential to ensure a quick and comprehensive assessment and global response.


    Table 1 Case-fatality rate (total number of cases) of laboratory-confirmed human infection with highly pathogenic avian influenza A (H5N1) virus by year of disease onset and country, 2003?2009

    [Country ? Year(a): 2003 - 2004 - 2005 - 2006 - 2007 - 2008 - 2009]

    • Cambodia ? Cambodge - ... (0) - ... (0) - 100 (4) - 100 (2) - 100 (1) - 0 (1) - 0 (1)
    • China ? Chine - 100 (1) - ... (0) - 62 (8) - 62 (13) - 60 (5) - 100 (4) - 57 (7)
    • Egypt ? ?gypte - ... (0) - ... (0) - ... (0) - 56 (18) - 36 (25) - 50 (8) - 10 (39)
    • Indonesia ? Indon?sie - ... (0) - ... (0) - 65 (20) - 82 (55) - 88 (42) - 83 (24) - 90 (21)
    • Viet Nam - 100 (3) - 76 (29) - 28 (61) - ... (0) - 62 (8) - 83 (6) - 100 (5)
    • All affected countries ? Ensemble des pays touch?s - 100 (4) - 74 (46) - 42 (104) - 70 (109) - 67 (88) - 75 (44) - 44 (73)

    (a) Values are % (total number of cases).

    (1) See No. 46, 2008, pp. 413?420.

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  • #2
    Re: WER Wkly Epidemiol Rec. Update on human cases of highly pathogenic avian influenza A (H5N1) infection: 2009

    The January FluTracker's summary (link) of H5N1 cases for 2009 only included 72 cases. Since then WHO has added one more case from <st1:country-region w:st="on"><st1:place w:st="on">Indonesia</st1:place></st1:country-region> for 2009. Also, at the time, there was no publically available demographic information on the cases from <st1:country-region w:st="on"><st1:place w:st="on">Indonesia</st1:place></st1:country-region>. Indonesia MOH must have provided detailed case information on these 21 cases because WHO has age and sex statistics for all 73 cases. Hopefully this demographic information from <st1:country-region w:st="on"><st1:place w:st="on">Indonesia</st1:place></st1:country-region> will be made available through retrospective Disease Outbreak News updates.
    The low median age was due primarily to the high proportion of cases occurring among children in Egypt; Egypt accounted for 53% of all cases worldwide. The age of cases in Egypt was notably younger than elsewhere, with a median age of 3 years; 80% of cases occurred in children aged <10 years. . . In all countries, the CFR was lower for cases aged <10 years than for cases aged >10 years (24% versus 71%; odds ratio [OR], 7.8; 95% confidence interval [CI], 2.7?22.4). . . The marked difference in the age distribution of cases among countries makes a direct comparison of risk factors difficult, given the relatively small total number of cases available for analysis.
    <!--[endif]-->
    The low CFR in Egypt in 2009 among young children (link) infected with H5N1 (a novel influenza virus) deserves further research especially in light of the high number of pediatric deaths from the novel pandemic virus, H1N1.
    http://novel-infectious-diseases.blogspot.com/

    Comment


    • #3
      Re: WER Wkly Epidemiol Rec. Update on human cases of highly pathogenic avian influenza A (H5N1) infection: 2009

      The two bits that caught my eye

      As in previous years,1 an increase in cases was reported during the northern hemisphere?s winter and spring seasons (Fig. 1). Reports of outbreaks among animals also tended to increase during the same period.
      Is this also true of poultry, pigs. horses and other animals that get types of flu? If it is then it mitigates against the 'flu increases in winter as people spend more time in close contact indoors' argument and points to a viral rather than host primary cause for seasonality.

      The rapid sharing of information globally is essential to ensure a quick and comprehensive assessment and global response.
      Now who could that little sting in the tail be aimed at? (rhetorical)

      Comment


      • #4
        Re: WER Wkly Epidemiol Rec. Update on human cases of highly pathogenic avian influenza A (H5N1) infection: 2009

        Volume 16, Number 1–January 2010 http://www.cdc.gov/eid/content/16/1/161.htm#1

        Letter

        Age-based Human Influenza A Virus (H5N1) Infection Patterns, Egypt
        Alan Schroedl

        Author affiliation: Anthrometrix Corporation, Salt Lake City, Utah, USA

        Suggested citation for this article

        To the Editor: In April 2009, a representative of the World Health Organization in Cairo voiced concern about the changing age-based pattern of human influenza A virus (H5N1) infection in Egypt (1). From March 2006 through July 2009, a total of 83 persons in Egypt were confirmed to have human influenza A (H5N1); the patients' ages ranged from >1 year to 75 years (2). However, from December 2008 through July 2009 in Egypt, 28 of 32 human infections were in children <8 years of age.

        The frequency of human influenza A virus (H5N1) infections parallels the pattern for seasonal influenza. Thus, for analytical purposes, virus subtype H5N1 infections in Egypt can be grouped into 12-month periods, beginning with August of 1 year and ending in July of the following year. The results for 1-way analysis of variance indicate that the age at time of virus subtype H5N1 infection in Egypt differs significantly among these 4 periods (Kruskal–Wallis test statistic = 20.732, p<0.0004 ).

        Further analysis shows that persons infected from August 1, 2008 through July 31, 2009, were much younger than those infected in the preceding 12-month period (Mann-Whitney U test statistic = 328.500, p<0.001). The median age of the 12 confirmed case-patients from August 1, 2007, through July 31, 2008, was 23.5 years, but the median age of the 33 confirmed case-patients from August 1, 2008, through July 31, 2009, was 3.0 years. The Table shows the distribution of case-patients by age group, the median age of each group, and the case-fatality ratio (CFR) for the 4 seasonal 12-month periods.

        This recent rise of subtype H5N1 influenza cases among children represents a major change in the pattern of human influenza A virus (H5N1) infections in Egypt compared with the pattern for earlier influenza seasons. Confirmation reports by the World Health Organization generally indicate associations with dead and sick poultry for these recent cases among children. The cultural patterns and customs of poultry husbandry have not changed in Egypt since the first human cases of influenza A (H5N1) were confirmed in 2006; thus, it is not clear why more children have been infected since December 2008. One explanation may be the increased recognition of the clinical signs of nonfatal influenza A (H5N1) among children and increased confirmation by laboratory testing. The lack of influenza A virus (H5N1) infection among the infected children's parents and caregivers suggests that the virus is still not easily transmissible among humans in Egypt.

        Not only has there been a recent increase in infections of influenza A (H5N1) among children, but there has also been a recent decline in deaths among confirmed infected persons. From 2006 through 2008, the annual CFR for influenza A (H5N1) in Egypt ranged from 36&#37; to 55% (3). Since January 1, 2009, the CFR in Egypt has been 11%. The recent increases in infections among children coupled with a decrease in the CFR in the most recent 12-month period suggests that the strain of influenza A virus (H5N1) now circulating in Egypt may be becoming less virulent as it continues to spread among young children, a segment of the population that is highly vulnerable to influenza infections (4,5).

        References
        Johnston C. Interview—concerns arise over symptomless Egypt bird flu cases. Reuters AlertNet, 08 Apr 2009 [cited 2009 Sep 17]. Available from http://www.alertnet.org/thenews/newsdesk/L7467886.htm
        World Health Organization. Situation updates—avian influenza [cited 2009 Sep 17] Available from http://www.who.int/csr/disease/avian.../en/index.html
        World Health Organization. Cumulative number of confirmed human cases of avian influenza A/(H5N1) reported to WHO [cited 2009 Nov 9]. Available from http://www.who.int/csr/disease/avian.../en/index.html
        Bhat N, Wright JG, Broder KR, Murray EL, Greenberg ME, Glover MJ, et al. Influenza-associated deaths among children in the United States, 2003–2004. N Engl J Med. 2005;353:2559–67. PubMed DOI
        Izurieta HS, Thompson WW, Kramarz P, Shay DK, Davis RL, DeStefano F, et al. Influenza and the rates of hospitalization for respiratory disease among infants and young children.. N Engl J Med. 2000;342:232–9. PubMed DOI
        Table
        Table. Age groups, median ages, and case-fatality ratios for influenza A (H5N1) case-patients, by influenza season, Egypt

        Suggested Citation for this Article
        Schroedl A. Age-based human influenza A virus (H5N1) infection patterns, Egypt [letter]. Emerg Infect Dis [serial on the Internet]. 2010 Jan [date cited]. Available from http://www.cdc.gov/EID/content/16/1/161.htm

        DOI: 10.3201/eid1601.090560

        Comment

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