Apr 20, 2004 (CIDRAP News) – Disease experts recently determined that a Yonkers, N.Y., man had H7N2 avian influenza last fall, but they have not been able to discern how he contracted it, according to a report in today's New York Times.
The case was apparently only the second known human case of avian flu in the United States. The Centers for Disease Control and Prevention (CDC) says that a Virginia poultry worker had a probable case of H7N2 avian flu during a major poultry outbreak there in 2002.
The Yonkers man, a Caribbean immigrant, was hospitalized last November with fever and cough and recovered after a few weeks, according to the Times report. Local experts suspected the virus was influenza A(H1N1) but were unsure, so they sent clinical samples to the CDC.
Because few H1N1 cases were reported last winter, the CDC didn't test the sample until February, according to the story. It was not until Mar 17 that scientists identified the virus as influenza A(H7N2). Further tests of blood samples from the patient, collected during his illness and more recently, showed antibodies to the H7N2 virus.
Human cases of avian flu have nearly always been linked with exposure to infected birds, but the Times report said authorities have found no evidence that the Yonkers man had direct contact with birds or had traveled to areas with avian flu outbreaks. Avian flu outbreaks on a few farms in Delaware, Maryland, and New Jersey in February were blamed on H7N2 viruses, the report noted.
County and state health officials have found no evidence that any of the patient's family members, co-workers, or other contacts had been infected, the story said. Nancy Cox, a CDC flu expert, was quoted as saying, "We can't figure out how he was exposed or why he's an isolated case."
Avian flu cases in people who have no history of exposure to birds raise concern about possible person-to-person transmission. Avian viruses rarely infect humans, and when they do, they usually are not passed easily to others. But disease experts fear that if the same person becomes infected with avian and human flu viruses, the viruses could combine into a dangerous new form that could pass easily from person to person.
In the recent H5N1 avian flu crisis in Asia, dozens of people in Vietnam and Thailand were infected and 24 died. But no human-to-human transmission has been reported in those outbreaks. More than 80 human cases of H7N7 avian flu, with one death, occurred in the Netherlands in 2003. But no person-to-person transmission was confirmed there either.
In addition, two human cases of H7 influenza have been confirmed in poultry workers in connection with the current outbreak of H7N3 avian flu in British Columbia, according to the CDC. Both workers recovered. Ten other poultry workers in the area also had suggestive symptoms.
The Times report said the CDC did not believe the New York case signaled an "imminent threat to public health."
Information on the CDC Web site says the previous probable human case of avian flu in the United States was linked to a 2002 Virginia outbreak in which 4.7 million chickens and turkeys were destroyed. A worker who helped cull flocks had upper respiratory symptoms and, when tested, was found to have antibodies to the H7N2 virus. But the virus was never isolated because no clinical samples were taken at the time. The worker, who fully recovered, could have been exposed while hunting wild birds, the agency says.
Apr 5 CDC report on previous human cases of influenza A(H7) in North America
CIDRAP overview: Avian influenza: Implications for Human Disease