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UDC 616-002.952:616.927-036.22(571.15)
ASSESSMENT OF THE EPIDEMIC SITUATION ON SIBERIAN TICKBORNE TYPHUS INCIDENCE AMONG THE POPULATION OF ALTAI KRAI IN 2000-2017
Altai State Medical University, Barnaul
A.V. Timonin, S.V. Shirokostup, N.V. Lukyanenko
The article presents the results of a retrospective epidemiological analysis of the incidence of the Altai Krai population with Siberian tick-borne typhus (STT), which is endemic in this region of the Siberian Federal District. The epidemiological situation on STT in the urban and rural areas of the region was assessed in the period from 2000 to 2017. Specific features of the incidence of STT among adults and children age cohorts of the population are determined. An assessment of the relationship between the trend in the dynamics of the incidence of STT and the number of people who have suffered from tick bites is made.
Key words: Siberian tick-borne typhus, natural focal infections, endemicity, prevention, Altai Krai.
Siberian tick-borne typhus (STT) is considered to be one of the most common diseases among other natural focal infections in Western Siberia. The regions of the Siberian Federal District, having numerous natural foci of this infection on its territory, make the greatest contribution to the structure of STT incidence in Russia. The absence of specific prophylaxis of STT, high frequency of contacts of the regional population with natural foci lead to the formation of a high incidence rate, significantly higher than the incidence rate of tickborne viral encephalitis in the same regions.
Altai Krai is endemic for STT. Geographical features of the region, diversity of flora and fauna, agricultural trend of the regional economy determine the situation in the region. A high percentage of the rural population in the region and the characteristic type of their professional and economic activity leading to a high frequency of long-term contacts of residents with natural foci of STT lead to high rates of annual registered incidence.
The research objective is to analyze the epidemic situation on Siberian tick-borne typhus among the urban and rural population of Altai Krai of various age groups in 2000-2017.
Materials and methods
The study involved the official reporting data from the Federal Service for Consumer Rights Protection and Human Welfare, the Center for Hygiene and Epidemiology in Altai Krai, the Ministry of Health of Altai Krai, the Federal Statistics Service for Altai Krai, data of statistical reporting forms No. 2 "Information on infectious incidence» in Altai Krai for 2000-2017. The statistical data processing was carried out in the program Statistica 12.0. In terms of the analysis, there was conducted the calculation of absolute and relative indicators, average values (X), errors of representativeness (± m), statistical significance (p) and Fisher's variance ratio (f).
Results and discussion
In our country, since the beginning of the official registration of cases of Siberian tick-borne typhus (STT) in 1936 and till 2017, more than 87 thousand cases of this disease have been registered. So, from 1936 to 2017, the incidence rate of this infection in Russia increased by 35 times, from 0,03±0,01 0/0000 to 1,06±0,03 0/0000. The average long-term incidence rate for this period constituted 0,82±0,03 0/0000.
Since the official registration of STT cases from 1945 to 2017, more than 32 thousand cases have been registered in Altai Krai. Thus, from 1945 to 2017, the incidence rates of STT increased by 3.4 times from 7,16±0,52 0/0000 to 24,56±1,02 0/0000. The average STT incidence rate in Altai Krai for the period of 1945-2017 reaches 16,69±0,79 0/0000, which is 18.8 times higher than the identical general indicator for Russia during the same period (0,89±0,03 0/0000).
The long-term dynamics of Siberian tick-borne typhus incidence, taking into account the changes in the trend direction, was divided into 4 periods.
The 1st period, from 1945 to 1954, was characterized by a tendency to an increase in incidence rates by 2.2 times (from 7,16±0,52 0/0000 to 16,06±0,77 0/0000). The average incidence rate in the 1st period was 9,48±0,59 0/0000. Such a tendency towards an increase in indicators in the long-term dynamics of incidence could be the reason for the active development of new territories in the region and, as a result, the frequent contact of the population with natural foci of infection. Also, the current situation could be conditioned by the start of official registration of STT cases among the local population of the region and improved clinical differential diagnosis of the disease.
In the 2nd period, from 1954 to 1973, the long-term dynamics of incidence was characterized by a tendency to decrease in indicators by 11.9 times (from с 16,06±0,77 0/0000 to 1,35±0,22 0/0000), with an annual rate of decline by averagely 4.6%. The average incidence of STT for the 2nd period consti-
tuted 4,36±0,40 0/0000. The current situation could have been caused by the use of DDT and HCH preparations as a means for large-scale acaricid-al treatments of the territories including aviation
technology. These activities could lead to an active reduction in the number of tick carriers and their hosts.
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Figure 1 - Long-term dynamics of Siberian tick-borne typhus incidence in Altai Krai in 1945-2017 (per 100 thousand population).
In the 3rd period, from 1973 to 2001, there was registered an increase in STT incidence by 52.1 times (1,35±0,22 0/0000 to 70,27±1,63 0/0000). The average incidence rate in the 3rd period constituted 21,38±0,89 0/0000. The current trend could be a consequence of the ban on the use of the highly effective drug DDT in the USSR since the 70s, which could have lead to a gradual increase in the number of tick-carriers, an increase in the activity of natural foci and an increase in the number of contacts of the regional population with the foci of this infection.
The 4th period, from 2001 to 2017, was characterized by a tendency to a decrease in STT incidence by 2.9 times (from 70,27±1,63 0/0000 to 24,56±1,02 0/0000). The average incidence rate in this period constituted 30,56±1,11 0/0000. The current situation could be a consequence of the introduction of laboratory confirmation of the diagnosis of the disease, an increase in the area of the territories treated with acaricides.
The autocorrelation method allowed to determine the cyclical nature of STT incidence in Altai Krai, which constituted 18 years.
STT incidence in Altai Krai covers differently various groups of the population. From 2000 to 2017, the long-term dynamics of STT incidence among the rural and urban population of the region had an unidirectional tendency to decrease in the incidence rates: for citizens - by 2.5 times (from 28,22±1,42 0/0000 to 11,27±0,92 0/0000) and by 2.2 times in rural population (from 89,78±2,68 0/0000 to 41,67±2,0 1 0/0000). However, the average long-term incidence rate among the rural population (52,33±2,16 0/0000) is 70.5% more than the same indicator among the urban population (15,46±1,07
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0000
The peak of the incidence registered among the urban population of the region was noted in 2001 (34,65±1,58 0/0000), the minimum - in 2011 (55,14±0,62 0/0000). The peak incidence among the rural population was also registered in 2001 (110,90±2,99 0/0000), the minimum incidence rates in 2013 (36,69±1,8006000/0000) and 2015 (36,45±1,87 0/0000).
The long-term dynamics of incidence among children under 17 years of age and the adult population of the region was characterized by a unidirectional tendency to decrease in rates: for adults - by 2.5 times (from 61,60±1,74 0/0000 to
25,03±1,16 0/0000), for children under 17 years old - by 1.9 times (from 42,92±2,6 1 0/0000 to 22,78±2,15 0/0000). The average long-term STT incidence among ad00u00lts (33,08±1,29 0/0000) for the period of 2000-2017 is higher than the same indicator among children under 17 years old (28,46±2,38 0/0000) by 14.0%. The peak incidence in the study period for both groups of the population was noted in 2001 for adults (74,95±1,92 0/0000), for children under 17 years of age (54,55±3,0 0/0000). Minimal STT incidence rates were
noted - among adults in 2011 (21,70±1,05 0/0000) and 2015 (21,39±1,06 0/0000), among children un00d00er 17 years of age - in 200(5 (5,89±1,10 0/0000).
For the study period from 2000 to 2017, the long-term dynamics of indicators of persons affected by a tick bite was characterized by a tendency to decrease by 15.1% (from 576,70±4,65 0/0000). The cyclical nature of
0/0000 to 500,87±4,59 this indicator established constituted 5 years.
by autocorrelation
Figure 2 - Long-term dynamics of Siberian tick-borne typhus incidence in Altai Krai in 2000-2017 (per 100 thousand population).
In the five-year period from 2000 to 2004, there was noted a strong direct correlation between the rates of those affected by the tick bite and the incidence of STT (r=0,85; p<0,001). In the period from 2005 to 2009, the presence of a direct weak correlation between similar indicators (r=0,38; p<0,001) was noted. The period of 2010-2014 characterized by the presence of a negative weak correlation between the current indicators (r=-0,22; p<0,001). The obtained results of the correlation for the study period may be a consequence of the change in the role and contribution of the indicator of victims of tick bite to the formation of STT incidence Altai Krai. Multidirectional tendencies, when there is a decrease in the incidence rate against the background of an increase in the number of people affected by tick bite, may indicate the presence of other factors affecting the incidence rate in the region.
Conclusion
Siberian tick-borne typhus is characterized by a wide distribution in Altai Krai. In the period from 2000 to 2017, there was a tendency to decline in all groups of the population, which
could be the result of the increase in the volume of nonspecific prophylaxis and the natural long-term cyclical nature of the disease constituting 18 years. Multifactorial influence on the formation of trends in STT incidence necessitates the conduct of comprehensive studies of the influence of natural and anthropogenic factors in the course of assessing the epidemic situation in the region.
As part of a retrospective analysis, a group of increased risk of STT incidence was identified - the rural working-age population over 18 years old. The activity of this category of the population is determined by the living conditions near natural foci of STT, a high frequency of contacts of the population with foci of infection due to the peculiarities of professional and household activities. The current situation indicates the need to develop preventive measures aimed at this group of the population.
The absence of possible specific prophylaxis in relation to STT necessitates an increase in the area of acaricidal treatments at the borders near settlements to reduce the number of ticks and, consequently, reduce the number of people affected by tick bites in cases of contact with anthropurgic
foci of infection. Nonspecific preventive measures aimed at preventing contact with a tick - carrier of infection, should also include more active sanitary and educational work among groups of professional and social risk. The implementation of a set of preventive measures in areas of Altai Krai that are endemic for STT will ensure a reduction in the incidence among the population and a reduction in the cost of healthcare for the treatment and rehabilitation of diseased persons.
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Contacts
Corresponding author: Timonin Andrey Viktorovich, Lecturer of the Department of Epidemiology, Microbiology and Virology, Altai State Medical University, Barnaul. 656031, Barnaul, ul. Papanintsev, 126. Tel.: (3852) 566924. Email: sekttor@mail.ru
Author information
Shirokostup Sergey Vasilyevich, Candidate of Medical Sciences, Associate Professor of the Department of Epidemiology, Microbiology and Virology, Altai State Medical University, Barnaul. 656038, Barnaul, Lenina Prospekt, 40. Tel.: (3852) 566869. Email: shirokostup@yandex.ru
Lukyanenko Natalia Valentinovna, Doctor of Medical Sciences, Professor of the Department of Epidemiology, Microbiology and Virology, Altai State Medical University, Barnaul. 656031, Barnaul, ul. Papanintsev, 126. Tel.: (3852) 566924. Email: natvalluk@mail.ru
