Puumala virus infections in Finland: Increased occupational risk for farmers

Puumala hantavirus, transmitted by bank voles (Clethrionomys glareolus), ca uses a mild-type hemorrhagic fever with renal syndrome. The disease is comm on in Finland and is considered an occupational hazard for farmers, but the actual risk has not been assessed by analytical studies. Data on 5,132 ser ologically confirmed Puumala virus infections during 1989-1994 were analyze d, and cases among farmers and the population living in similar conditions were compared. The farmers contracted the disease earlier and more often th an did the comparison group. In the province of Mikkeli with the highest in cidence (70/100,000), the risk ratio was 5.1 (95% confidence interval (CI) 3.0-8.4) for 20- to 29-year-old farmers; in the older age groups, the risk was still increased but the risk ratios were lower. The peak incidence in t he comparison group was 10 years later (age group 30-39 years). For the who le country, the result was similar although less marked. The average risk r atio adjusted by age, sex. and geographic variation was 1.7 (95% CI 1.5-1.8 ) for the whole country and 1.9 (95% CI 1.5-2.3) for the Mikkeli province, where 80% of Puumala virus infections among young farmers could be estimate d to be attributable to occupation.