Multiple sclerosis in Key West, Florida.

In 1984, a press release by a Miami, Florida, neurologist described a possible cluster of persons with multiple sclerosis in Key West, Florida. The authors examined the cluster using prevalence rates, which are recognized as having a latitudinal gradient for multiple sclerosis, being generally high at high latitudes and low at low latitudes. Case ascertainment showed 32 definite or probable cases among residents of the study area (latitude, 24.5 degrees N) on September 1, 1985, a prevalence rate of 70.1/100,000 population--14 times the rate estimated for this latitude by modeling techniques based on US and international data, 7-44 times the rate for areas at similar latitudes (Mexico City, Mexico; Hawaii; New Orleans, Louisiana; and Charles County, South Carolina), and 2.5 times the expected rate for all US latitudes below 37 degrees N. This finding could not be explained by changes in diagnostic criteria, case ascertainment bias, immigration of people from high-risk areas, an unusual population structure, a large percentage of related cases, or better survival. Prevalent cases (n = 22) were more likely than general population controls (n = 76), matched by sex and 10-year age group, to have: lived longer in Key West, been a nurse, ever owned a Siamese cat, had detectable antibody titers to coxsackievirus A2 and poliovirus 2, and ever visited a local military base (Fleming Key). Key West has an unusually high prevalence of multiple sclerosis that may be related to these risk factors.