Changes in the Epidemiology of Zoonotic Infections in Children: A Nationwide Register Study in Finland

Zoonotic infections are difficult to recognize in children. The age distributions and seasonal occurrences of these infections vary substantially, even among those transmitted by the same vectors, and their epidemiology may change over time. The aim was to report the incidences and trends of Borrelia burgdorferi, Puumala virus, Francisella tularensis and tick-borne encephalitis (TBE) virus infections in the pediatric population (age 0–19) of Finland. METHODS: A nationwide survey based on the National Infectious Disease Register was conducted from 1996 to 2019 and all laboratory-confirmed cases were included. Age-stratified incidences per 100,000 person-years were calculated. RESULTS: Cumulative incidences were B. burgdorferi 11.2, TBE 0.4, Puumala virus 6.4 and F. tularensis 2.5 per 100,000 person-years. An increasing trend in the incidences of B. burgdorferi and TBE was observed. Borrelia expanded geographically northward and inland. Tularemia follows a 2–4-year epidemic cycle and rates are similar across age groups. Puumala incidences are highest in the older children. DISCUSSION: Borrelia infections increased most rapidly in children 5–9 years of age and overall expanded geographically in Finland. Tularemia epidemic cycles were shorter than those previously reported. These results will help clinicians to identify these infections in different geographic areas and age groups in Finland.