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 . . .