Epidemiology and Infection

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Epidemiology and Infection (2010), 138:576-584 Cambridge University Press
Copyright © Cambridge University Press 2009

Original Papers

Other viruses

Case-control study on Puumala virus infection: smoking is a risk factor

K. VAPALAHTIa1a2, A.-M. VIRTALAa3, A. VAHERIa1a2 and O. VAPALAHTIa1a2a3 c1

a1 Department of Virology, Haartman Institute (Haartmaninkatu 3), University of Helsinki, Helsinki, Finland
a2 Department of Virology, Helsinki University Hospital Laboratory (HUSLAB), Helsinki, Finland
a3 Department of Basic Veterinary Sciences, Faculty of Veterinary Medicine, University of Helsinki, Helsinki, Finland
Article author query
vapalahti k [PubMed]  [Google Scholar]
virtala am [PubMed]  [Google Scholar]
vaheri a [PubMed]  [Google Scholar]
vapalahti o [PubMed]  [Google Scholar]


Puumala hantavirus (PUUV) is apparently transmitted to humans by inhalation of aerosolized secretions of carrier rodents (bank voles). The means of transmission and the associated risk factors are poorly defined. An epidemiological study during the peak of an epidemic season in Finland was conducted based on 282 acute clinical PUUV infections and 204 controls without PUUV infection or immunity. The main risk factors adjusted by age, sex and living environment were cigarette smoking [odds ratio (OR) 3·6, 95% confidence interval (CI) 2·1–5·9, P<0·0001] and buildings with holes allowing rodents to enter (OR 3·3, 95% CI 2·0–5·6); these results were similar in two subsets. Further, use of rodent traps (OR3·5, 95% CI 2·2–5·7) and handling firewood (OR 2·7, 95% CI 1·6–4·4) were associated with a risk. The risk attributed to smoking also remained high using simulated population controls with average smoking habits. The results suggest that hantavirus transmission occurs by inhalation mainly indoors and is dependent on the condition of the respiratory tract.

(Accepted August 12 2009)

(Online publication September 28 2009)

Key Words:Cigarette smoking; haemorrhagic fever with renal syndrome (HFRS); hantavirus; Puumala virus; rodents


c1 Author for correspondence: Dr O. Vapalahti, Haartman Institute, Department of Virology, P.O. Box 21 (Haartmaninkatu 3), FIN-00014 University of Helsinki, Finland. (Email: olli.vapalahti@helsinki.fi)