To the Editor.
—In 1988, investigation of a fatal case of swine influenza in a previously healthy 32-year-old pregnant woman provided strong evidence for transmission of swine influenza virus infection from ill pigs to humans during a Wisconsin agricultural fair, in which 40% to 60% of exhibited pigs had an influenza-like illness.1The results of this investigation led to prospective surveillance for ill pigs at Wisconsin agricultural fairs in 1989 and 1990 to assess the frequency with which visitors to these fairs might be exposed to outbreaks of symptomatic swine influenza. Between May 1976 and June 1977, a serosurvey of pigs from north central states slaughtered at abattoirs in Wisconsin showed that swine influenza virus infections of pigs are common and may have an October-through-December seasonality.2In 1989, veterinarians responsible for 32 county or state fairs held in the southern two thirds of Wisconsin between July and September
Chapman L, Wells D, Schonberger L, Davis JP, Hinshaw V, Easterday BC. Swine Influenza Surveillance, Wisconsin Agricultural Fairs, 1989 and 1990. JAMA. 1992;267(20):2741. doi:10.1001/jama.1992.03480200049021