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Multiple sclerosis in Key West, Florida

C G Helmick1, J M Wrigley, M M Zack

  • 1Division of Chronic Disease Control, Center for Environmental Health and Injury Control, Atlanta, GA.

American Journal of Epidemiology
|November 1, 1989
PubMed

Insights

A multiple sclerosis (MS) cluster in Key West, Florida, showed a prevalence rate 14 times higher than expected for its low latitude. Potential risk factors identified include prolonged residence, nursing as an occupation, Siamese cat ownership, and specific viral antibody titers.

Area of Science:

  • Epidemiology
  • Neurology
  • Environmental Health

Background:

  • Multiple sclerosis (MS) prevalence typically exhibits a latitudinal gradient, increasing with higher latitudes.
  • A 1984 press release suggested a potential MS cluster in Key West, Florida, a low-latitude region.
  • Investigating this anomaly is crucial for understanding MS distribution and potential environmental influences.

Purpose of the Study:

  • To investigate the reported cluster of multiple sclerosis (MS) in Key West, Florida.
  • To determine the prevalence rate of MS in Key West and compare it to expected rates.
  • To identify potential risk factors associated with MS in this unique low-latitude population.

Main Methods:

  • Prevalence rates were calculated based on case ascertainment of definite or probable MS cases among Key West residents as of September 1, 1985.
  • The identified prevalence rate was compared to modeled rates for the latitude and similar low-latitude regions.
  • A case-control study compared prevalent MS cases (n=22) with matched population controls (n=76) to identify risk factors.

Main Results:

  • A prevalence rate of 70.1/100,000 population was found, 14 times higher than expected for Key West's latitude (24.5 degrees N).
  • This rate was significantly higher than in other low-latitude areas and exceeded the expected rate for all US latitudes below 37 degrees N.
  • Identified risk factors for MS cases included longer residence in Key West, nursing as an occupation, Siamese cat ownership, specific viral antibody titers (coxsackievirus A2, poliovirus 2), and prior visits to Fleming Key.

Conclusions:

  • Key West exhibits an unusually high prevalence of multiple sclerosis (MS) that cannot be explained by conventional factors.
  • The study suggests potential environmental or exposure-related risk factors unique to the Key West environment may contribute to MS.
  • Further research into identified risk factors such as viral exposure and environmental characteristics is warranted to elucidate MS etiology in this region.

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