Zavadska et al.
Tick-borne encephalitis: A 43-year summary of epidemiological and clinical data from Latvia (1973 to 2016).
PLoS ONE 2018; e0204844, https://doi.org/10.1371/journal.pone.0204844
Based on national legislation, a countrywide mandatory case-based passive reporting system is in place in Latvia since 1973. However,the ECDC case definition for TBE was not used in Latvia until officially adopted in 2012. Since 2006, Latvia has a National TBE Immunization Program which provides TBE vaccines free of charge to children living in highly endemic areas. From 1973 through 2016, a total number of 15,193 TBE cases were reported to the Centre for Disease Prevention and Control, of which 2819 were reported from 2007 to 2016. In addition, 104 TBE cases have been analyzed by review off our hospital databases. From all 2923 reported cases, 1973 cases met the ECDC TBE case definition criteria. The highest average 10-year incidence was observed from 1990 to 1999 with 27.9 cases per 100,000 population, while the average 10-year incidence from 2007 to 2016 was 9.6 cases per 100,000 population. The high number of reported cases during the period 1990 to 1999 may have resulted based on a mix of several factors, e.g. more outdoor activities (collecting mushrooms) during the political and socio-economic changes in 1989, increased use of serological confirmation of TBE infections and increased awareness resulting in more testing.
Most of the cases from 2007 to 2016 occurred in adults (95.1%) and the most common clinical form was meningitis (90.6%). Alimentary TBE cases were considered in 0.7%. According to hospital records, 1.6% of patients had been vaccinated with at least one dose and 98.2% of patients were not vaccinated. That means that TBE occurs almost entirely in the unvaccinated population. There was an increasing TBE vaccine uptake from 39% in 2005 to 52.5% by 2015. Moreover, TBE vaccine uptake by children reached 22% nationwide, and was as high as 77% in highly endemic areas. The incidence of TBE in Latvia varies annually and is difficult to predict. However, the decrease in incidence may be the result of the national TBE immunization program.
The epidemiological data presented here may be compared with the neighboring country Lithuania (Snapshot week 14) and with European data discussed in the Newsletter of November.