Affiliations: *Thamasart University Hospital, Pratumthani, Thailand
**National Institute of Health, Nonthaburi, Thailand
***Siriraj Hospital, Bangkok, Thailand
****Washington University School of Medicine, St. Louis, Missouri, USA
Source: Emerging Infectious Diseases 2004 Jul; 10(7): 1321-4
Influenza A viruses are classified into subtypes (hemagglutinin and neuraminidase subtypes) based on antigenic differences in their surface glycoproteins. Of 15 identified hemagglutinin (H1-H15) and 9 neuraminidase subtypes (N1-N9), only 3 hemaglutinin subtypes (H1, H2 and H3) and 2 neuraminidase subtypes (N1 and N2) have established stable lineages in humans. Because the natural reservoir of known influenza A subtypes is found in birds and waterfowl, subtypes other than those typicaly found in humans have the potential to cross the species barrier and infect humans.
Avian influenza A virus H9N2 was isolated from two children in Hong Kong in 1999 and avian influenza H7N7 infected 89 persons during a simultaneous outbreak in poultry in the Netherlands in 2003, although these infections resulted in only mild illnesses. The first outbreak of a highly pathogenic avian influenza (H5N1) in humans occurred in Hong Kong in 1997; 6 of 18 people with confirmed infection died. Despite attempts to prevent disease, two cases of influenza A H5N1 occurred in Hong Kong in February 2003, Followed by outbreaks in Vietnam ant Thailand in January 2004. Data are limited on the epidemiologic characteristics, signs and symptoms and outcomes of avian influenza H5N1 exposure in healthcare workers. We report atypical avian influenza H5N1 and follow-up surveillance of 35 exposed healthcare workers; we also review relevant literature in this area.