Disease burden of Puumala virus infections, 1995-2008

(Accepted 23 December 2009; first published online 29 January 2010)SUMMARYPuumala virus (PUUV) causes mild haemorrhagic fever with renal syndrome, a rodent-bornezoonosis. To evaluate the disease burden of PUUV infections in Finland, we analysed datareported by laboratories to the National Infectious Disease Registry during 1995–2008 andcompared these with data from other national registries (death, 1998–2007; hospital discharge,1996–2007; occupational diseases, 1995–2006). A total of 22681 cases were reported (averageannual incidence 31/100000 population); 85% were in persons aged 20–64 years and 62% weremales. There was an increasing trend in incidence, and the rates varied widely by season andregion. We observed 13 deaths attributable to PUUV infection (case-fatality proportion 0.08%).Of all cases, 9599 (52%) were hospitalized. Only 590 cases (3%) were registered as occupationaldisease, of which most were related to farming and forestry. The wide seasonal and geographicalvariation is probably related to rodent density and human behaviour.Key words: Emerging infections, epidemiology, hantavirus.INTRODUCTIONPuumalavirus(PUUV)infection,alsoknownasneph-ropathia epidemica, is a zoonotic disease mainlycharacterized by sudden onset of fever, myalgias,headache and occasionally renal failure [1]. Bankvoles (Myodes glareolus) are the host reservoir ofPUUV, a member of the rodent-borne Hantavirusgenus of the family Bunyaviridae. PUUV can remaininfectious in bank-vole cage beddings for 12–15days [2]. The route of infection to humans is believedto occur through aerosolized rodent excreta.Exposure may occur during a variety of occupationaland recreational activities, such as working withhay, cleaning barns or summer cottages, cuttingwood and entering buildings infested with rodents,especially when the premises are poorly ventilated[1, 3]. The incubation period varies between 2 and 6weeks [4]. Diagnosis is based on serological tests, de-tection of PUUV IgM or low avidity of PUUV IgG,