Socio-economic conditions and other anthropogenic factors influencing tick-borne encephalitis incidence in the Czech Republic.

Abstract

Laboratory confirmed cases of tick-borne encephalitis (TBE) have been reported in the Czech Republic since 1971. Peaks of incidence occurred at 2 to 5-year intervals. The incidence in the eighties was generally lower than in seventies. In the nineties there was a sharp increase in incidence that peaked in 1995 (7.2/100,000). TBE cases occur from April to November with maximum incidence in July. During the last decade the second peak of incidence occurred in most years in September and/or October. In the last decade, an extension of the TBE season towards the spring and autumn periods has been observed. In addition to a general increase in TBE incidence in the last decade, some other changes in the epidemiology of TBE were observed in the Czech Republic. During the whole period sex-specific incidence was higher in men than in women (men to women ratio 1.5:1). Age-specific incidence over recent years increased steadily in children and adolescent age groups. In the ten-year age groups from 25 to 65, it remains practically at the same level (6-8/100,000). In older persons it fell to 2-3/100,000. Tick bites infect patients mainly during their recreational activities. A very small proportion (less than 1%) acquires the infection through the alimentary route. We have tested the hypothesis whether the increase in TBE incidence in the nineties was due to economical or social changes after the velvet revolution of 1989. Between 1991 and 1995 unemployment largely remained on the same level (between 2-3%). Over the next years the percentage of unemployed persons increased rapidly to 9.3% in 1999 (7.8% in 2001). This trend differs significantly from the trend of TBE incidence that peaked in 1995. No correlation between the district incidence of TBE and the district percentage of unemployment in the years 1997-2001 was found (r=-0.20). The percentage of unemployed persons among the TBE cases was 1-3% in contrast to the Czech Republic figures which were 5-9% for the same period. The gross domestic product in USD per capita increased from dollars 2,600 in 1991 to dollars 5,000 in 1995. Since then it has varied between dollars 4,800 and dollars 5,600. This trend, therefore, differs from the trend of TBE incidence as well. Among the TBE cases the percentage of foresters and other persons working in the forests in the years 1997-2001 was 0.5-1%. The behavioral and socio-economic aspects of TBE cases remained stable despite the political changes which have take place in the Czech Republic since the beginning of the nineties. They are not, therefore, responsible for the increased TBE incidence. In the industrial areas most polluted by SO2 in the past in northern Bohemia the sharp increase in TBE incidence seems to be connected with measures aiming to eliminate SO2 emissions from brown coal power stations.