St. Louis encephalitis: clinical and epidemiologic aspects, Mississippi, 1974.

During July, August, and September 1974, 23 confirmed or presumptive cases of St. Louis encephalitis occurred in Mississippi. Attack rates were highest in the northwest corner of the state and among persons over 70 years of age. Rural and urban residents had similar attack rates. Nine persons have not resumed their pre-illness level of activity because of residual neurologic impairment six months after their illness. Additional cases of St. Louis encephalitis are expected in the next few years.