Analysis of the Lyme Borreliosis Epidemiological Indicators in Latvia and Seropositivity Associated Factors. Summary of the Doctoral Thesis

Abstract

The thesis “Analysis of the Lyme borreliosis epidemiological indicators in Latvia and seropositivity associated factors” is dedicated to one of the topical tick-borne infectious diseases in Latvia and in the world during recent years. Estimates suggest that every year in Europe Lyme borreliosis affects about 85 000 people and the incidence has recently increased sharply in many European countries. Increase in incidence to some extent is related to the diagnosis and reporting improvement, although there is evidence of a true increase in incidence in relation to many natural and socio-economic factors. Experts consider that the actual number of Lyme borreliosis cases 2–3 times exceeds the number reported in the passive reporting system. Lyme borreliosis in Latvia is a subject to mandatory reporting and registration, however, the available statistical data, like other countries, does not reflect the true burden of the disease for the public health and economy. Use of the serological diagnostic methods of Lyme borreliosis is limited by the relatively slow production of antibodies in the early stages of infection, antibody association with infective genospecies, as well as by sufficiently high antibody seroprevalence among European citizens, therefore leading European experts believe that Lyme borreliosis clinical and laboratory diagnosis requires development of the best practice guidelines for doctors, and rational laboratory testing and treatment promotion. The aim of this thesis was to carry out an epidemiological analysis of Lyme borreliosis morbidity in the period from 2007 to 2011 in Latvia, and to identify factors associated with serological confirmation of the diagnosis. For the implementation of the aims: a systematic selection of the data has been performed for Lyme borreliosis cases registered in the period from 2007 to 2011 from the State Communicable Disease Surveillance and Monitoring System (VISUMS); the data reporting completeness has been analyzed, comparing Lyme borreliosis cases included in VISUMS database with the data from the Management Information System (VIS); epidemiological features of Lyme borreliosis in 2007–2011 have been analyzed in relation to the climatic, natural, environmental and social factors, tick activity, number of tick hosts, and tick-borne encephalitis epidemiological features; factors associated with serological confirmation of the diagnosis have been analyzed. The following methods are used in this work: calculation of incidence rates and 95% confidence interval by territories, gender and age groups, as well as occupational status; calculation of the relative risk in incidence comparisons, time series analysis, using the linear single- and multiple regression models, correlation analysis with some climatic, natural, characterizing anthropogenic pollution and social factors. Binary and multinomial logistic regression statistical models are used for multivariate analysis and association between specific factors and outcome is expressed in the form of an odds ratio – OR. Data analysis has been performed using MS Excel, WinPepi, STATISTICA and SPSS software. The results of this work revealed that Lyme borreliosis incidence was rising since the start of registration. During the study period, the incidence rate increased by 41% and the increase was more evident in I. persulcatus tick distribution area (in the eastern part of the country). It is estimated that Lyme borreliosis incidence changes are associated with an impact of natural (number of tick hosts, the forest areas), environmental (pollution) and climate factors (air temperature, rainfall abundance during the tick activity season). The study demonstrated that Lyme borreliosis incidence varied in different gender and age groups: women are significantly more likely to become ill than men, and adults – more often than children, and relatively more often than representatives of the groups in other countries. It was found that Lyme borreliosis incidence rate among unemployed persons is higher than that for employed, pointing to strong association of employment factor with the disease risk. The study found that anatomical sites of a tick bite is different in patients with different Lyme borreliosis clinical forms, children and adults, and living in I. ricinus and I. persulcatus distribution areas. Differences in the frequency of Lyme borreliosis clinical forms in the statistical and tick distribution regions found in this study are due to differences in Borrelia prevalence level in ticks, as well as due to reporting deficiencies in certain areas. The study proved that the reporting of Lyme borreliosis in Latvia is incomplete, however cases are representative of all cases. Factors associated with a positive serological investigation result are identified in the study: elevated odds for IgM antibodies in ELISA test for women, younger patients, and patients who did not have Lyme borreliosis erythema migrans form; elevated odds for IgG class antibodies in ELISA test for elderly patients, patients without Lyme borreliosis erythema migrans, living in I. ricinus distribution area. In addition, elevated odds for IgG class antibodies in the elderly patients and rural population indirectly indicates a relatively great prevalence of antibodies against B. burgdorferi s.l. in Latvia population. The results of this thesis provide a basement to improve epidemiological surveillance system, to ensure preparation of more qualitative information for development and evaluation of complex of the prophylaxis measures, as well as to develop evidence-based guidelines for the algorithm of laboratory investigation of the Lyme borreliosis cases.