Is clinical primary care surveillance for tularaemia a useful addition to laboratory surveillance? An analysis of notification data for Finland, 2013 to 2019

Background: In Finland, surveillance of tularaemia relies on laboratory-confirmed case notifications to the National infectious Diseases Register (NIDR). Aim: The aim of the study was to assess the suitability and usefulness of clinical surveillance as an addition to lab-orator y notification to improve tularaemia surveillance in Finland. Methods: We retrieved NIDR tularaemia surveillance and primary healthcare data on clinically diagnosed tularaemia cases in Finland between 2013 and 2019. We compared incidences, demographic distributions and seasonal trends between the two data sources. Results: The median annual incidence was 0.6 (range: 0.1-12.7) and 0.8 (range: 0.6-7.2) per 100,000 for NIDR notifications and primary healthcare notifications, respectively. Cases reported to NIDR were slightly older than cases reported to primary healthcare (median: 53 years vs 50 years, p = 0.04), but had similar sex distribution. Seasonal peaks differed between systems, both in magnitude and in timing. On average, primary healthcare notifications peaked 3 weeks before NIDR. However, peaks in NIDR were more pronounced, for example in 2017, monthly inci-dence per 100,000 of NIDR notifications peaked at 12.7 cases in September, while primary healthcare notifica-tions peaked at 7.2 (1.8 ratio) in August. Conclusions: Clinically diagnosed cases provide a valuable addi-tional data source for surveillance of tularaemia in Finland. A primary healthcare-based system would allow for earlier detection of increasing incidences and thereby for early warning of outbreaks. This is crucial in order to implement targeted control and prevention