Human Puumala hantavirus infection in northern Sweden; increased seroprevalence and association to risk and health factors.

BACKGROUND: The rodent borne Puumala hantavirus (PUUV) causes haemorrhagic fever with renal syndrome in central and northern Europe. The number of cases has increased and northern Sweden has experienced large outbreaks in 1998 and 2006-2007 which raised questions regarding the level of immunity in the human population. METHODS: A randomly selected population aged between 25 and 74 years from northern Sweden were invited during 2009 to participate in a WHO project for monitoring of trends and determinants in cardiovascular disease. Health and risk factors were evaluated and sera from 1,600 participants were available for analysis for specific PUUV IgG antibodies using a recombinant PUUV nucleocapsid protein ELISA. RESULTS: The overall seroprevalence in the investigated population was 13.4 %, which is a 50 % increase compared to a similar study only two decades previously. The prevalence of PUUV IgG increased with age, and among 65-75 years it was 22 %. More men (15.3 %) than women (11.4 %) were seropositive (p < 0.05). The identified risk factors were smoking (OR = 1.67), living in rural areas (OR = 1.92), and owning farmland or forest (OR = 2.44). No associations were found between previous PUUV exposure and chronic lung disease, diabetes, hypertension, renal dysfunction, stroke or myocardial infarction. CONCLUSIONS: PUUV is a common infection in northern Sweden and there is a high life time risk to acquire PUUV infection in endemic areas. Certain risk factors as living in rural areas and smoking were identified. Groups with increased risk should be targeted for future vaccination when available, and should also be informed about appropriate protection from rodent secreta.