Disease transmitted by ticks is Rocky Mountain spotted fever (
Ticks are now accepted as both the vector and the reservoir for the CCHF virus. It is declared that the distribution and reservoirs of the known tick types get common additional globalisation and constantly increasing international animal transportation cause the spread of pathogens and vectors globally [
The first CCHF case in Turkey was reported in 2002 in Tokat province [
World-wide map of CCHF distribution [
Mortality rates change in accordance with the geographical region (4–20%) and with this high mortality rate; CCHF is an important public health problem in Turkey [
The population-based cross-sectional study was carried out in the city of Tokat, which is in the middle Black Sea region of Turkey. In this study, the population of Tokat province ≥20 years consists of 412.653 individuals. In calculating the sample size, the expected prevalence of the disease to be investigated was found to be 50%, the deviation was taken as 0.05, and the design effect was taken as 2 at 97% confidence level and the population targeted to be reached with the Epi Info version 7 program was found to be 2635.
The sample selection was made by multi-layer proportional cluster sampling method considering the size of the urban and rural settlements of the provincial centres and districts in the Tokat provincial population pyramid, gender, and age groups. A total of 85 Family Medicine Units (FMU) from over 170 in Tokat were randomly selected using a 50% sampling. Each FMU was considered as a cluster. By using the quota sampling method in the intracluster sample, the number of individuals required to fall to the determined gender and age groups is provided to work. The gender and age groups whose numbers were set for each cluster were randomly selected by systematic sampling method after ranking by Family Medicine Information System. The participants included in the study were invited to the FMUs. All participants signed a voluntary consent form. Those who reported cognitive impairment that would prevent the questionnaire forms from understanding or giving clear answers and those who declared that they were pregnant were excluded from the study.
For the data collection, a questionnaire about the sociodemographic characteristics and CCHF-related risk factors of the participants was completed by face-to-face interviews by physicians in study group and blood samples were taken from the participants for laboratory tests. The sera obtained by centrifuging the samples were stored at +4°C and then transferred to a −70°C unit at the end of the day until further analysis could be performed. Anti-CCHFV IgG were studied by serum in the Public Health Institution of Turkey Microbiology Reference Laboratory. Specific IgG antibody level against CCHFV was measured in serum with the Enzyme-Linked Immuno Sorbent Assay (ELISA) method which is a method that can be used in serosurveillance studies. 92% (2428) of the sample calculated in the study was reached. As a result, the data of 2319 (88%) participants were included in the statistical analysis due to insufficient blood samples or inability to analyze serum samples from 109 participants. The dependent variables were anti-CCHFV IgG serology and evaluated in two categories as seropositive and seronegative. The independent variables were some descriptive characteristics and CCHF-related risk factors.
The data analysis was performed using SPSS 22.0. Categorical variables were summarized by number, percentage, mean ± standard deviation (min-max), and 95% confidence interval, compared with Pearson Chi-square and Fisher’s exact tests. Logistic regression analysis was used for the descriptive and CCHF-related risk factors for anti-CCHFV IgG seropositivity. The values of
The study was approved by the Ethical Committee of Tokat Gaziosmanpaşa University Faculty of Medicine (approval number: 14-KAEK-142). A written informed consent was obtained from each participant.
54.9% (1272) of 2319 participants were female, and the mean age was 47.3 ± 15.3 (20–87 ages). 69.2% of the participants lived in the districts, 58.3% of them were graduates of primary and secondary school, 47.9% of them were housewives, 86.8% were married, and 51.3% had poor level of family income (Table
Distribution of the participants according to some descriptive characteristics.
Variables | Categories | |
---|---|---|
Gender | Female | 1272 (54.9) |
Male | 1047 (45.1) | |
Age groups | 20–39 years | 925 (39.9) |
40–64 years | 1025 (44.2) | |
≥65 years | 369 (15.9) | |
Residential area | City center | 714 (30.8) |
Districts | 1605 (69.2) | |
Education level | Illiterate-literate | 412 (17.8) |
Primary school-secondary school | 1353 (58.3) | |
High school-university | 554 (23.9) | |
Occupation | Housewife | 1110 (47.9) |
Farmer | 351 (15.1) | |
Worker | 224 (9.7) | |
Retired | 203 (8.8) | |
Other (officer, tradesman, others) | 431 (18.6) | |
Marital status | Married | 2012 (86.8) |
Single | 142 (6.1) | |
Divorced | 165 (7.1) | |
Family income status | Bad | 1189 (51.3) |
Medium | 718 (31) | |
Good | 412 (17.8) | |
Chronic disease | No | 1087 (46.9) |
Yes | 1232 (53.1) | |
Smoking | No | 1451 (62.6) |
Yes | 868 (37.4) | |
Alcohol use | No | 2104 (90.7) |
Yes | 215 (9.3) | |
Obesity (body mass index ≥30 kg/m2) | No | 1416 (61.1) |
Yes | 903 (38.9) | |
Total | 2319 (100.0) |
According to some risk factors for CCHF of the participants, 41.6% of them lived in rural areas, 15.1% were farmers, 33.1% were involved in animal husbandry, and 16% had tick-contact history. 1% of the participants had hospitalization history with suspected CCHF, 7% of those had a relative with history of CCHF treatment, and in the area where 15.5% of participants lived there were people diagnosed with CCHF (Table
Distribution of participants according to their characteristics related to some risk factors for CCHF.
Variables | Categories | |
---|---|---|
Location | Urban | 1354 (58.4) |
Rural | 965 (41.6) | |
Farming | No | 1968 (84.9) |
Yes | 351 (15.1) | |
Animal husbandry | No | 1551 (66.9) |
Yes | 768 (33.1) | |
Having a pet at home | No | 1910 (82.4) |
Yes | 409 (17.6) | |
Tick contact history | No | 1949 (84) |
Yes | 370 (16) | |
Duration of contact with tick contact ( | ≤1 year | 123 (33.2) |
2–4 years | 114 (30.8) | |
≥5 years | 133 (35.9) | |
Hospitalization with suspected CCHF | No | 2295 (99) |
Yes | 24 (1) | |
Is there anyone in your family who was treated for CCHF? | No | 2157 (93) |
Yes | 162 (7) | |
If there is anyone in your family who was treated for CCHF, what is the health status? ( | Is alive | 149 (92) |
Is dead | 13 (8) | |
Is there anyone diagnosed with CCHF where you live? | No | 1959 (84.5) |
Yes | 360 (15.5) | |
If there is anyone diagnosed with CCHF where you live, what is the health status? ( | Is alive | 242 (67.2) |
Is dead | 118 (32.8) | |
Total | 2319 (100.0) |
Anti-CCHFV IgG seropositivity was 5.6% (
Comparison of anti-CCHF IgG seropositivity frequency in females and males by age groups of the participants.
Age groups | Female | Male | Total | |||||
---|---|---|---|---|---|---|---|---|
Seropozitivity | Seropozitivity | Seropozitivity | ||||||
20–29 | 169 | 3 (1.8) | 0.001 | 124 | 2 (1.6) | <0.001 | 293 | 5 (1.7) |
30–39 | 357 | 7 (2.0) | 275 | 10 (3.6) | 632 | 17 (2.7) | ||
40–49 | 220 | 8 (3.6) | 167 | 10 (6.0) | 387 | 18 (4.7) | ||
50–59 | 228 | 11 (4.8) | 228 | 19 (8.3) | 456 | 30 (6.6) | ||
≥60 years | 298 | 24 (8.1) | 253 | 36 (14.2) | 551 | 60 (10.9) | ||
Total | 1272 | 53 (4.2) | 1047 | 77 (7.4) | 2319 | 130 (5.6) |
Anti-CCHFV IgG, anti-Crimean–Congo haemorrhagic fever virus immunoglobulin G.
In the logistic regression analysis of the descriptive characteristics of the participants in terms of anti-CCHFV IgG seropositivity (Table
Logistic regression analysis of the descriptive characteristics of the participants in terms of anti-CCHFV IgG seropositivity (
Variables | Anti-CCHFV IgG | COR (95% CI) | AOR (95% CI) | |||
---|---|---|---|---|---|---|
Seropozitivity | Seronegativity | |||||
Gender | Female | 53 (4.2) | 1219 (95.8) | 0.001 | Ref. | Ref. |
Male | 77 (7.4) | 970 (92.6) | 1.83 (1.27–2.62) | 2.53 (1.57–4.08) | ||
Age groups | 20–39 years | 22 (2.4) | 903 (97.6) | <0.001 | Ref. | Ref. |
40–64 years | 57 (5.6) | 968 (94.4) | 2.42 (1.47–3.99) | 1.84 (1.05–3.20) | ||
≥65 years | 51 (13.8) | 318 (86.2) | 6.58 (3.93–11.03) | 4.05 (2.14–7.65) | ||
Residental area | City center | 43 (6) | 671 (94) | 0.561 | Ref. | |
Districts | 87 (5.4) | 1518 (94.6) | 0.89 (0.61–1.30) | |||
Education level | Illiterate-literate | 46 (11.2) | 366 (88.8) | <0.001 | Ref. | Ref. |
Primary-secondary | 71 (5.2) | 1282 (94.8) | 0.44 (0.30–0.65) | 0.49 (0.30–0.80) | ||
High school-university | 13 (2.3) | 541 (97.7) | 0.19 (0.10–0.36) | 0.33 (0.14–0.76) | ||
Marital status | Married | 111 (5.5) | 1901 (94.5) | 0.014 | Ref. | Ref. |
Single | 3 (2.1) | 139 (97.9) | 0.37 (0.12–1.18) | 0.89 (0.25–3.170) | ||
Divorced | 16 (9.7) | 149 (90.3) | 1.84 (1.06–3.19) | 1.30 (0.70–2.42) | ||
Family income level | Bad | 87 (7.3) | 1102 (92.7) | <0.001 | Ref. | Ref. |
Medium | 33 (4.6) | 685 (95.4) | 0.61 (0.40–0.92) | 0.93 (0.59–1.46) | ||
Good | 10 (2.4) | 402 (97.6) | 0.32 (0.16–0.61) | 0.71 (0.33–1.52) | ||
Chronic disease | No | 53 (4.9) | 1034 (95.1) | 0.151 | Ref. | |
Yes | 77 (6.3) | 1155 (93.8) | 1.30 (0.91–1.87) | |||
Smoking | No | 86 (5.9) | 1365 (94.1) | 0.385 | Ref. | |
Yes | 44 (5.1) | 824 (94.9) | 0.85 (0.58–1.23) | |||
Alcohol use | No | 120 (5.7) | 1984 (94.3) | 0.523 | Ref. | |
Yes | 10 (4.7) | 205 (95.3) | 0.81 (0.42–1.56) | |||
Obesity (BMI ≥ 30 kg/m2) | No | 83 (5.9) | 1333 (94.1) | 0.503 | Ref. | |
Yes | 47 (5.2) | 856 (94.8) | 0.88 (0.61–1.27) | |||
Total | 130 (5.6) | 2189 (94.4) |
Anti-CCHFV IgG, anti-Crimean–Congo haemorrhagic fever virus immunoglobulin G; COR, crude odds ratio; AOR, adjusted odds ratio; CI, confidence interval; Ref, reference;
In the logistic regression analysis of some CCHF-related risk factors in terms of anti-CCHFV IgG seropositivity of the participants, it was identified that farming, dealing with animal husbandry, history of tick contact, and history of hospitalization with suspected CCHF and being anyone diagnosed with CCHF in the place of residence significantly affected the seropositivity. Seropositivity rates in terms of AOR were higher 1.84 times in farmers (AOR: 1.84; 95%CI: 1.18–2.86;
Logistic regression analysis of some CCHF-related risk factors for anti-CCHFV IgG seropositivity of the participants (
Variables | Anti-CCHFV IgG | COR (95% CI) | AOR (95% CI) | |||
---|---|---|---|---|---|---|
Seropozitivity | Seronegativity | |||||
Location | Urban | 70 (5.2) | 1284 (94.8) | 0.28 | Ref. | |
Rural | 60 (6.2) | 905 (93.8) | 1.22 (0.85–1.74) | |||
Farming | No | 93 (4.7) | 1875 (95.3) | <0.001 | Ref. | Ref. |
Yes | 37 (10.5) | 314 (89.5) | 2.38 (1.59–3.54) | 1.84 (1.18–2.86) | ||
Animal husbandry | No | 66 (4.3) | 1485 (95.7) | <0.001 | Ref. | Ref. |
Yes | 64 (8.3) | 704 (91.7) | 2.05 (1.43–2.92) | 1.64 (1.04–2.27) | ||
Having a pet at home | No | 104 (5.4) | 1806 (94.6) | 0.467 | Ref. | |
Yes | 26 (6.4) | 383 (93.6) | 1.18 (0.76–1.84) | |||
Tick contact history | No | 93 (4.8) | 1856 (95.2) | <0.001 | Ref. | Ref. |
Yes | 37 (10) | 333 (90) | 2.22 (1.49–3.30) | 1.02 (1.03–2.29) | ||
Duration of with tick contact | ≤1 year | 15 (12.2) | 108 (87.8) | 0.293 | Ref. | |
2–4 years | 13 (11.4) | 101 (88.6) | 0.93 (0.42–2.04) | |||
≥5 years | 9 (6.8) | 124 (93.2) | 0.52 (0.22–1.24) | |||
Hospitalization with suspected CCHF | No | 121 (5.3) | 2174 (94.7) | <0.001 | Ref. | Ref. |
Yes | 9 (37.5) | 15 (62.5) | 10.78 (4.62–5.13) | 6.65 (2.70–16.43) | ||
Is there anyone in your family who was treated for CCHF? | No | 117 (5.4) | 2040 (94.6) | 0.165 | Ref. | |
Yes | 13 (8) | 149 (92) | 1.52 (0.84–2.77) | |||
If there is anyone in your family who was treated for CCHF, what is the health status? ( | Is alive | 11 (7.4) | 138 (92.6) | 0.308 | Ref. | |
Is dead | 2 (15.4) | 11 (84.6) | 2.28 (0.45–11.61) | |||
Is there anyone diagnosed with CCHF where you live? | No | 95 (4.8) | 1864 (95.2) | <0.001 | Ref. | Ref. |
Yes | 35 (9.7) | 325 (90.3) | 2.11 (1.41–3.17) | 1.66 (1.08–2.56) | ||
If there is anyone diagnosed with CCHF where you live, what is the health status? ( | Is alive | 22 (9.1) | 220 (90.9) | 0.563 | Ref. | |
Is dead | 13 (11) | 105 (89) | 1.24 (0.60–2.55) |
Anti-CCHFV IgG, anti-Crimean–Congo haemorrhagic fever virus immunoglobulin G; COR, crude odds ratio; AOR, adjusted odds ratio; CI, confidence interval;
Although the morbidity and mortality of CCHF in Tokat province, where CCHF is endemic, have been reported to be decreasing compared with previous years [
Anti-CCHFV IgG seropositivity was found as 5.6% (
In a systematic review that examined the seroprevalence studies in Turkey, CCHF seroprevalence was reported as 0.5%–19.6% [
In our study, anti-CCHFV IgG seropositivity was 4.2% in females and 7.4% in males. The mean age was significantly higher in seropositive. Seropositivity was highest in the age group of ≥60 (10.9%) and increased with advancing age. Seropositivity was statistically significantly higher in males and age group ≥65 years. In our study, the male gender was found to be a risk factor for CCHF similar to the study representing the seven geographical regions of Turkey [
In our study, low education and low-income levels were found to be risk factors for anti-CCHFV IgG seropositivity. Seropositivity was lower in graduated from high school and in those with good income significantly (
In the literature, it has been stated that living in rural areas is a risk factor in terms of exposure to ticks and CCHF [
Many studies have shown that the history of tick bite is an important risk factor for CCHF [
This study has some limitations. First of all, since it is a cross-sectional study, it can only be generalized to the province of Tokat where the study was conducted. Second, since only individuals ≥20 years old were included in our study, it is not possible to obtain information about CCHF seroprevalence in younger age group. Finally, it should not be disregarded that the actual prevalence could be higher than the identified as there may be people who have been exposed to the CCHFV and whose anti-CCHFV IgG antibodies have not been detected at a diagnostic level as a consequence of antibody level decrease following years of the infection. Despite all these limitations, in terms of the identification of CCHF seroprevalence and relevant risk factors at utmost accuracy, one of the strengths of the study that it was conducted not among the patients referred to healthcare centres or occupationally risky group but among a seemingly healthy population included in a layered sample representing the community in general based on gender, age group, and urban or rural residents in Tokat province located in Kelkit Basin where it is endemic for CCHF in Turkey. Besides, the participation rate to the study is quite sufficient for such a field study.
In conclusion, in this population-based epidemiological study conducted in adults aged ≥20 years in Tokat in the endemic region, it was found that CCHF seroprevalence is common. Anti-CCHFV IgG seropositivity was significantly high in males, advanced age group, low-educated, low-income, farming and/or animal husbandry, history of tick contact, hospitalization with suspected CCHF, and having individuals with diagnosed CCHF in the place of residence. The results of our study revealed the necessity of increasing measures for public health. It should be kept in mind that CCHF control is not only the duty of healthcare professionals, but multisectoral cooperation is required within the framework of the “One Health” concept. As CCHF is a common and important public health issue, such studies to be realized to identify the seroprevalence in regional and national level with community-based approach gain more importance.
The raw data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that they have no competing interests.
This work was carried out in collaboration between all authors. RÇ, ME, and FD designed the study. RÇ, YÖ, YEB, ÖY, NYÇ, and ŞŞ involved in data collection. RÇ and YÖ conducted the data analysis. RÇ, ME, YÖ, and FD prepared the manuscript draft. All the authors read and approved the final version of the manuscript.
The authors would like to thank all healthcare professionals of Tokat Public Health Directorate for their support during the data collection, Tokat Gaziosmanpaşa University Scientific Research Projects Commission for financial support, Selcuk Kılıç and Dilek Yağçı Caglayik for support during the analysis performed in the Public Health Institution of Turkey Microbiology Reference Laboratory, and Osman Demir for support in statistical analysis and all other staff who contributed to the study. This study was supported by the Scientific Research Projects Unit of Tokat Gaziosmanpaşa University (Project Number: 2014/55).