A pseudo-outbreak of influenza A associated with use of laboratory stock strain.

In November 1982, when influenza type A(H3N2) viruses were spreading in the United States, influenza A(H1N1) viruses were reportedly isolated from 10 hospitalized patients in New Mexico, only two of whom had influenza-like illnesses. Reference stock influenza A/Fort Monmouth (FM)/1/47(H1N1) virus had been used to prepare fluorescent antibody test slides in the laboratory reporting the isolates. After investigation, it was concluded that the isolates from the patients' cultures were a result of laboratory contamination. When an unexpected cluster of unusual virus isolates is reported, the possibility of laboratory contamination should be considered.