Avian Influenza Update, September 19, 2005
By Luciana Borio, M.D., and John Bartlett, M.D., September 19, 2005
Indonesia on High Alert
Indonesia is on high alert for avian influenza and is preparing 44 hospitals to care for infected patients in the event of a larger epidemic. These precautions are being taken in response to the suspicion that two children have contracted the disease, one of whom was the nephew of a woman who died from pneumonia and an influenza-like illness earlier this month (Bloomberg, Sept. 19). Four people in Indonesia have already died from avian influenza this year, and public health systems are monitoring for additional cases. Human contact with infected poultry, particularly sick or dying chickens, is thought to be the primary mode of disease transmission in Asia, where live poultry markets are not uncommon, and many people raise chickens in their backyards.
In the Literature
In a recent article in the Journal of Infectious Diseases (J Infect Dis. 2005 Oct 15;192(8):1311-4), Frederick Hayden and Alice Croisier discuss possible patterns of transmission of avian influenza viruses to and between humans. They highlight two main points: 1) Serosurveillance studies are making it increasingly apparent that some avian influenza viruses are more likely than others to infect humans. 2) Human influenza viruses are thought to be transmitted by direct contact with infectious droplets, including inoculation of the upper respiratory tract or conjunctival mucosa, or inhalation of airborne droplet nuclei. The authors posit that avian influenza viruses may transmit via additional routes, thus complicating usual infection control precautions. H5N1 viral RNA has been consistently detected in fecal samples (and infected birds shed high concentrations of virus in feces), raising the possibility that the virus may replicate in the human gastrointestinal tract and that human feces may be a source of transmission. Infection after consumption of undercooked poultry has been suspected in some cases.
The authors also point out that avian influenza infection in humans may present in atypical ways, that is, in ways other than acute respiratory illness. For example, the H7 subtype of avian influenza virus typically causes conjunctivitis, while infection with H5N1 commonly leads to diarrhea.
The preponderant risk factor for the acquisition of H5N1 infection is contact with infected poultry. However, approximately 30% of H5N1-infected patients in Vietnam did not report such exposure in a study done by the World Health Organization in 2005 (World Health Organization. WHO consultation on case management and research on human influenza A/H5. Hanoi, Vietnam, 10-12 May 2005). This would suggest that either such contact was underreported or human-to-human transmission is more common than thought. A better understanding of the multiple potential routes of disease transmission is extremely important to the worldwide effort to prepare healthcare and disease-containment systems for an influenza pandemic.