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Atypical H5N1 Human Infections - ProMED

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  • Atypical H5N1 Human Infections - ProMED

    A ProMED-mail post
    ProMED-mail is a program of the
    International Society for Infectious Diseases

    Date: Mon 4 Sep 2006
    From: Stephen M. Apatow <>

    Comments on WHO Case Definitions and Atypical H5N1 Infections
    In the context of the WHO case definitions for human infections with
    influenza A(H5N1) virus, it appears that atypical infections continue
    to be excluded from the potential clinical spectrum of challenge:
    (29 Aug 2006), or ProMED-mail post "Avian influenza, human (133):
    WHO case definitions" 20060830.2467.

    WHO has defined a suspect case as: A person presenting with
    unexplained acute lower respiratory illness with fever (>38 C [100.4
    F]) and cough, shortness of breath or difficulty breathing. And one
    or more of the following exposures in the 7 days prior to symptom
    a. Close contact (within 1 metre) with a person (e.g. caring for,
    speaking with, or touching) who is a suspected, probable, or
    confirmed H5N1 case;
    b. Exposure (e.g. handling, slaughtering, defeathering, butchering,
    preparation for consumption) to poultry or wild birds or their
    remains or to environments contaminated by their faeces in an area
    where H5N1 infections in animals or humans have been suspected or
    confirmed in the last month;
    c. Consumption of raw or undercooked poultry products in an area
    where H5N1 infections in animals or humans have been suspected or
    confirmed in the last month;
    d. Close contact with a confirmed H5N1 infected animal other than
    poultry or wild birds (e.g. cat or pig);
    e. Handling samples (animal or human) suspected of containing H5N1
    virus in a laboratory or other setting.

    However, the following references indicate that atypical infections
    (encephalitis, diarrheal, gastrointestinal illness) are a serious
    concern associated with outbreaks of avian influenza A subtype H5N1
    worldwide (See:
    <>: Emerging
    Infectious Diseases, Vol. 10, No. 7, July 2004; and
    <>, NEJM, Volume
    352:686-691, 17 Feb 2005, Number 7).

    Furthermore, European researchers have reported what they call the
    first evidence that low-pathogenic avian influenza (LPAI) viruses,
    and not just highly pathogenic (HPAI) strains like H5N1, can infect
    humans. The finding, in a study of Italian poultry workers, suggests
    that avian influenza viruses have more chances than previously
    suspected to mix with human influenza viruses, potentially creating
    hybrids that could trigger a human influenza pandemic, according to a
    report published online by the Journal of Infectious Diseases (See:
    Low-pathogenic Avian Influenza (LPAI) Viruses Can Infect Humans
    and ProMED-mail post "Avian influenza, human: LPAI susceptibility"

    Diarrhea and the detection of viral RNA in most fecal samples tested
    has been a frequent observation suggesting that H5N1 virus may
    replicate in the human gastrointestinal tract. This raises the
    question of whether human feces could be a source of transmission.
    (See the Editorial Commentary on the Puzelli et al. paper by
    Frederick Hayden and Alice Croisier in the journal of Infectious D
    onlineiseases of 15 Oct 2005

    Examples of Asymptomatic Human Infection
    (1) Four South Koreans were infected with the H5N1 strain of bird flu
    in late 2003 and early 2004, but none of them developed any serious
    illness, an official said 24 Feb 2006. (See:

    (2) Three asymptomatic infections have been documented among close
    contacts of confirmed cases in Viet Nam suggesting that milder H5N1
    infections are occurring. Four persons who culled H5N1 infected birds
    in Japan and 2 animal attendants caring for infected tigers in
    Thailand also have antibodies to H5 virus. Asymptomatic infections
    were also detected retrospectively in Hong Kong following the 1997
    outbreak. (See:

    (3) On 9 Mar 2005 Vietnamese health authorities released information
    about 2 such cases. Nguyen Tran Hien, director of the National
    Institute for Hygiene and Epidemiology, confirmed that lab tests
    showed that a 61-year-old woman from northern Thai Binh province had
    contracted the H5N1 virus but was not showing any symptoms. (See:

    (4) Two elderly relatives of people in Vietnam who died of bird
    influenza have tested positive for the disease, despite having no
    symptoms. Samples from another 7 cases that originally tested
    negative in Viet Nam in January were re-tested in Tokyo and found to
    carry the virus, according to the World Health Organization. (See:

    (5) Dr Charoen Chuchottaworn, a bird-flu expert at the [Thai] Public
    Health Ministry's Department of Medical Services, said doctors
    concluded after reviewing the history of the past 2 cases that
    bothvictims presented very mild symptoms of avian influenza and
    neither had any physical contact with chickens or birds. (See:

    While much has been made of the fulminant cases of presumed viral
    pneumonia in 1918, Dr. Brundage's research indicates that the
    majority of pneumonia cases, even in 1918, were either secondary
    bacterial pneumonias following an influenza infection or mixed viral
    and bacterial pneumonias. In the pre-antibiotic era, these cases of
    bacterial pneumonia carried a very high mortality rate; however, with
    appropriate antibiotic therapy, many such patients may be saved.

    Stephen M. Apatow

    [There is still a deficit of comprehensive seroprevalence data to
    establish the true frequency of subclinical infections and the
    relevance of these sporadic accounts of atypical infections listed
    above. For a discussion of this topic and an evaluation of some
    published seroprevalence studies, the reader is referred to the
    ProMED-mail posts archived as Avian influenza, human - Eurasia (41):
    multicountry 20060130.0290 and Avian influenza, human - East Asia
    (195): China 20051208.3538. - Mod.CP]

    [see also:
    Avian influenza, human (133): WHO case definitions 20060830.2467
    Avian influenza, human - Eurasia (41): multicountry 20060130.0290
    Avian influenza, human - East Asia (195): China 20051208.3538
    Avian influenza, human: LPAI susceptibility 20050918.2759]

  • #2
    Re: Atypical H5N1 Human Infections - ProMED

    Very interesting.

    a. Close contact (within 1 metre) with a person (e.g. caring for,
    speaking with, or touching) who is a suspected, probable, or
    confirmed H5N1 case;