Incidence of Tick-Borne Encephalitis in the Czech Republic in 2001–2011 in Different Administrative Regions and Municipalities with Extended Power

Summary

Aim:
Analysis of the incidence of tick-borne encephalitis (TBE) in the Czech Republic (CR) in 2001–2011 in different administrative regions and municipalities with extended power (MEPs).

Material and methods:
Each TBE case reported to the EPIDAT system was matched to the respective MEP or Prague according to the place of residence. The annual TBE incidence was calculated per 100 000 permanent residents (mean) of each administrative region and MEP. The overall incidence, age-specific incidence, and average incidence by administrative region per year and per the eleven-year period were calculated.

Results:
In the study period, the highest TBE incidence rates were found in the Plzeň Region, South Bohemian Region, and Highlands Region, neighbouring with Germany and Austria. The overall TBE incidence in the CR had a slightly upward trend resulting from different subtrends in various administrative regions.

The overall trend was most influenced by the most affected regions with opposite trends – the Highlands Region and the South Bohemian Region. The South Bohemian Region with the highest average incidence in the study period of 23.4/100 000 population also showed the maximum effect on the country-wide age-specific incidence due to the trend in the age--specific incidence, sharply rising to peak in the age group 60-64. As it had long been the region with the highest incidence in the Czech Republic, vaccination campaigns were organized repeatedly there, targeting high-risk areas and children. The vaccine coverage rate in school-age children in the last decade was about 50%. The analysis of age group trends showed no considerable increase in 0–14-year-olds in 2011, i.e. the year with the second highest TBE incidence ever reported in the CR, in contrast to 15 to 44-year-olds where the TBE incidence rates were three times as high. From this it can be inferred that the post-vaccination antibody level and its protective effect wane over years unless a booster dose is given. The incidence trend for TBE in 45–64-year-olds, i.e. the age group who lived life long inside or close to the most active TBE foci, suggests that the contact with the TBE virus does not induce protective herd immunity.

The analysis of TBE incidence in the population of smaller administrative areas provides more detailed information. In six MEPs, the average TBE incidence over the 11-year period was more than 30/100 000, with a peak of 58/100 000.

Conclusion:
Although the most important epidemiological information for a disease with natural focality is the place of acquisition of infection, the long-term evaluation of TBE incidence according to the patient’s place of residence is also relevant. The data on TBE incidence in the population of 205 MEPs provide helpful information for campaigns to reduce the risk of TBE infection targeted to human behaviour in TBE natural foci and preventive measures, particularly vaccination. It cannot be excluded that residents of high-risk areas will continue risky behaviour even in the future.

Keywords:
tick-borne encephalitis – incidence – municipalities with extended power – diseases with natural focality