Introduction
Avian influenza outbreaks among poultry occur worldwide from time to time. Avian influenza viruses can be classified into low pathogenicity and highly pathogenic forms based on the severity of the illness they cause in poultry. Most strains of avian influenza are classified as low pathogenicity avian influenza (LPAI) and cause few clinical signs in infected birds. In contrast, high pathogenicity avian influenza (HPAI) causes a severe and extremely contagious illness and death among infected birds. LPAI poses no known serious threat to human health, however some strains of HPAI viruses can be infectious to people. Most recently, outbreaks of highly pathogenic avian influenza A (H5N1) among poultry have been associated with illness and death in humans in Asia, Africa, Europe, the Pacific, and the Near East. In the United States, from 1997 to 2005, there were 16 outbreaks of low pathogenic avian influenza A viruses (H5 and H7 subtype) and one outbreak of highly pathogenic avian influenza A (H5N2) in poultry.
North American Outbreaks With Transmission to Humans
H7N3 in Canada, 2004
On February 19, 2004 , the Canadian Food Inspection Agency announced an outbreak of avian influenza A (H7N3) in poultry in the Fraser Valley region of British Columbia . Culling operations and other measures were performed in an effort to control the spread of the virus. Health Canada reported two cases of laboratory-confirmed influenza A (H7): one in a person involved in culling operations on March 13-14, and the other in a poultry worker who had close contact with poultry on March 22-23. Both patients developed conjunctivitis (eye infection) and other flu-like symptoms. Their illnesses resolved after treatment with the antiviral medication oseltamivir.
Although these are the only laboratory-confirmed cases of avian influenza A (H7) in humans during this outbreak in Canada , approximately 10 other poultry workers exhibited conjunctival and/or upper respiratory symptoms after having contact with poultry. Use of personal protective equipment is mandatory for all persons involved in culling activities, and compliance with prescribed safety measures is monitored. Epidemiologic, laboratory, and clinical evaluation is ongoing, as is surveillance for signs of avian influenza in exposed persons. There is currently no evidence of person-to-person transmission of avian influenza from this outbreak. For more information about this outbreak, visit the Canadian Food Inspection Agency website at http://www.inspection.gc.ca/english/anima/heasan/disemala/avflu/situatione.shtml .
H7N2 in New York, 2003
In November 2003, a patient with serious underlying medical conditions was admitted to a hospital in New York with respiratory symptoms. One of the initial laboratory tests identified an influenza A virus that was thought to be H1N1. The patient recovered and went home after a few weeks. Subsequent confirmatory tests conducted in March showed that the patient had been infected with an H7N2 avian influenza A virus.
North American Outbreaks Among Poultry With No Transmission to Humans
H5N2 in Texas, 2004
In February 2004, an outbreak of highly pathogenic avian influenza (HPAI) A (H5N2) was detected and reported in a flock of 7,000 chickens in south-central Texas . This was the first outbreak of HPAI in the United States in 20 years.
H7N2 in Delaware, New Jersey, and Maryland, 2004
In February 2004, an outbreak of low pathogenic avian influena (LPAI) A (H7N2) was reported on 2 chicken farms in Delaware and in four live bird markets in New Jersey supplied by the farms. In March 2004, surveillance samples from a flock of chickens in Maryland tested positive for LPAI H7N2. It is likely that this was the same strain.
