Avian Influenza and the Specter of Pandemic Influenza

Since December 2003, outbreaks of highly pathogenic avian influenza A(H5N1) among poultry have been reported in Cambodia, China, Indonesia, Japan, Laos, South Korea, Thailand, and Vietnam. Cases of H5N1 influenza have been demonstrated in humans living in many areas where avian outbreaks have occurred. As of February 16, 2004, 28 cases of laboratory-confirmed influenza A(H5N1) virus infections in humans, resulting in 20 deaths, have been reported in Thailand and Vietnam. In addition, approximately 100 suspected cases in humans are under investigation by national health authorities in Thailand and Vietnam. The Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO), the World Organization for Animal Health (OIE), and national health authorities in Asian countries are working to assess and monitor the situation, provide epidemiologic and laboratory support, and assist with control efforts.

Please note, that though there have also been recent reports of avian influenza outbreaks in Delaware, New Jersey, British Columbia and Pakistan, the H7 strain responsible for these outbreaks is considered to have low pathogenicity and is not currently seen as a threat to humans.

The rapid spread of highly pathogenic avian H5N1 influenza, with outbreaks occurring at the same time in several countries, is historically unprecedented and poses a considerable human public health risk because not only can these viruses infect humans, causing severe disease with high mortality, but there is also potential for them to adapt, or recombine with other influenza viruses, and give rise to a pandemic viral strain. The current H5N1 strain circulating in Asia appears to be highly pathogenic for humans, and immunity in the human population is generally lacking. However, the strain has not been shown to be easily transmitted between humans, and sustained person-to-person transmission has not occurred. If the virus continues to circulate widely among poultry, it has a greater potential to infect humans and other animals (such as pigs), where genetic re-assortment could take place and create a new pandemic strain.

The majority of the human H5N1 cases are apparently associated with direct exposure to infected birds or to surfaces contaminated with excretions from infected birds. A family respiratory illness cluster in Vietnam suggests the possibility of limited person-to-person transmission.

Current Recommendations for Healthcare Providers

The clinical presentation and travel history of persons with influenza A(H5N1) or SARS-CoV infection may overlap. A complete travel and epidemiological (exposure) history should be taken from persons presenting with respiratory infections. Public Health and hospital infection control should be notified when patients meet screening criteria for SARS or avian influenza. For current SARS screening criteria, see: www.metrokc.gov/health/sars/screening.htm

All patients who present to a health-care setting with fever and respiratory symptoms should be managed according to recommendations for respiratory hygiene and cough etiquette (www.cdc.gov/flu/professionals/infectioncontrol/resphygiene.htm). Isolation precautions identical to those recommended for SARS should be implemented for all hospitalized patients diagnosed with or under evaluation for influenza A(H5N1).

Laboratory Guidelines for H5N1 Influenza

Highly pathogenic avian influenza A(H5N1) must be worked with under Biosafety Level (BSL) 3+ laboratory conditions, including controlled access double door entry with change room and shower, use of respirators, decontamination of all wastes, and showering out of all personnel. The same BSL 3+ laboratory guidelines are recommended for conducting virus isolation for SARS-CoV. CDC recommends that laboratories not culture influenza virus from patients suspected to have H5N1 influenza unless stringent BSL 3+ conditions can be met. Therefore, respiratory virus cultures should not be performed in most clinical laboratories and such cultures should not be ordered for patients suspected of having H5N1 infection. Clinical specimens from suspect A(H5N1) cases and SARS-CoV cases may be tested by PCR assays using standard BSL 2 work practices in a Class II biological safety cabinet. In addition, commercial antigen detection testing can be conducted under BSL 2 levels to test for influenza.