Sales of nonprescription cold remedies: a unique method of influenza surveillance.

In 1976, the National Institute of Allergy and Infectious Disease sponsored a nationwide network for influenza surveillance. In this paper, in addition to reporting the surveillance findings in Los Angeles, sales of nonprescription cold remedies in a large supermarket chain were evaluated as an indicator of influenza activity in the community. Twenty-seven isolates of influenza B occurred between February 17 and April 26, 1977. Peak influenza B activity occurred from mid-March to early April, 1977. A 5-10% increase in percent of respiratory and febrile respiratory illness seen in outpatient clinics was observed in late December and January. No variation in these statistics occurred during the peak of influenza activity. In contrast, sales of nonprescription cold remedies were apparently influenced by influenza B activity. Peak sales (345% increase) occurred 4 wk after the first influenza B isolate and 1 wk before peak influenza activity was documented by peak rates of isolation.