H1N1 Influenza A Disease — Information for Health Professionals

In the first 2 weeks in April, cases of infection with an untypable influenza A virus began to be identified in Mexico and southern California. 1 Although the exact sequence of events is uncertain, by the third week of April it was established that the illness resulted from a triple recombination of human, avian, and swine influenza viruses; the virus has been found to be H1N1. This virologic analysis allowed for the development of a polymerase-chain-reaction (PCR) test to determine whether, in any given person, illness with the protean manifestations of cough, fever, sore throat, diarrhea, and nausea could be confirmed . . .