Detecting Avian Influenza A Virus Infection in Humans
Avian influenza A virus infection in humans cannot be diagnosed by clinical signs and symptoms alone; laboratory testing is required. Avian influenza A virus infection is usually diagnosed by collecting a swab from the nose or throat of the sick person during the first few days of illness. This specimen is sent to a lab; the laboratory looks for avian influenza A virus either by using a molecular test, by trying to grow the virus, or both. (Growing avian influenza A viruses should only be done in laboratories with high levels of protection).
For critically ill patients, collection and testing of lower respiratory tract specimens may lead to diagnosis of avian influenza virus infection. For some patients who are no longer very sick or who have fully recovered, it may be difficult to find the avian influenza A virus in the specimen, using these methods. Sometimes it may still be possible to diagnose avian influenza A virus infection by looking for evidence of the body's immune response to the virus infection by detecting specific antibodies the body has produced in response to the virus. This is not always an option because it requires two blood specimens (one taken during the first week of illness and another taken 3-4 weeks later). Also, it can take several weeks to verify the results, and testing must be performed in a special laboratory, such as at CDC.