in june and september 2006 , persons living in 56 villages of the 14 districts of tokat and sivas provinces ( figure 1 ) who had a risk for cchfv infection other than occupational risk ( i.e. , healthcare , slaughterhouse work , and veterinary care ) were randomly selected for the study .
villages and districts were selected based on residences of patients who were diagnosed with cchfv infection and treated at cumhuriyet university hospital , sivas , turkey , during the 2005 cchfv outbreak .
men and women were included in the study , but children < 7 years of age were excluded because of difficulties in drawing blood samples and obtaining parental consent . using epi info version 6 software ( centers for disease control and prevention , atlanta ,
ga , usa ) and assuming a cchfv seroprevalence of 10% in the study population with 99% confidence levels , we calculated error limits of  3% and a design effect of 1 .
the estimated sample size required was 664 , but the target sample size of high - risk persons was increased to 782 .
another 100 persons who were not at high risk for cchfv infection , but who lived in urban areas in the high - risk region and agreed to provide blood samples , were also included in the study .
the cchfv seroprevalence study team in turkey included a physician and a nurse who went to the selected villages and approached the heads of the village and selected families .
they explained the objectives of the study and asked for written informed consent from participants or parents of participating minors and then administered an interview - based questionnaire and collected a blood sample .
the questionnaire considered the following variables : age ; sex ; history of tick bite , tick removal from animals , animal abortion , and animal slaughtering activity ; close contact with a cchfv patient or an animal ; and occupation .
blood samples ( 10 ml each ) were collected and later tested for antibodies to cchfv by using immunoglobulin g ( igg ) elisa kits ( vector - best ; kolsovo , novosibirsk , russia ) .
spss version 10.0 ( spss , chicago , il , usa ) for windows software was used for statistical analysis .
univariate analysis was used to identify the risk factors for seropositivity of cchfv in the 782 participants . of the 782 high - risk persons ,
forty - seven ( 12.1% ) of 390 female participants and 53 ( 13.5% ) of 392 male participants were seropositive for cchfv ( p>0.05 ) .
of the 100 serum samples collected in the urban population , only 2 ( males 44 and 56 years of age ) were seropositive .
the cchfv seroprevalence in the 782 persons at high risk increased significantly with age ( p<0.001 ) . the highest proportion ( 23.5% ) of seropositivity
was found in persons 6170 years of age ( p<0.001 ) ( table 1 ) .
figure 2 shows distribution of the cchfv seroprevalence in high - risk persons by age groups .
the only variables significantly associated with presence of antibody against cchfv were history of tick bite ( p = 0.002 ) or of tick removal from the animals ( p = 0.03 ) , employment in animal husbandry ( p = 0.01 ) or farming ( p = 0.02 ) , and age > 40 years ( p<0.001 ) ( table 2 ) .
p value = 0.59 for persons living in rural area ; for persons living in urban area , data are insufficient for statistical analysis . 
p value < 0.001 for persons living in rural area ; for persons living in urban area , data are insufficient for statistical analysis .
distribution of seroprevalence of immunoglobulin g against crimean - congo hemorrhagic fever virus by age groups for 782 high - risk persons living in rural areas of tokat and sivas provinces , turkey , 2006 . * cchfv , crimean - congo hemorrhagic fever virus .
serologic evidence of cchfv in turkey was reported in the 1970s ( 4 ) . in 2003 ,
the cchfv seroprevalence among 40 veterinarians in the tokat region was 2.5% ( 5 ) .
another seroprevalence study conducted in 2003 among healthcare workers providing care to cchfv patients in turkey detected no seropositive persons ( 6 ) . the present survey indicates that the seroprevalence of cchfv is higher in persons living in rural areas than in urban areas of the cchfv epicenter in turkey ( 12.8% vs 2.0% ) . however , because special markets for animal trading are located on the outskirts of large cities in iran , cchfv seroprevalence was found to be higher among persons living in urban areas than in persons living in rural areas of this country ( 7 ) .
living in a rural area is a risk factor for exposure to the tick vector and for acquiring cchfv infection ( 8,9 ) .
expected seroprevalence of cchfv among high - risk persons during epidemics has been found to be 10% ( 3 ) ; however , seroprevalence has been reported to be as low as 0.5% in nonepidemic situations ( 10 ) .
other studies conducted in rural parts of iran and senegal during epidemics showed that the cchfv seroprevalence was 13% , comparable to our findings ( 9,11 ) . in the present study , history of tick bite and history of tick removal from animals
the overall tick - bite frequency was 62% ( 483/782 ) among persons at high risk and has been reported among 40%60% of cchfv patients in turkey ( 4 ) .
we also determined that the occupations of animal husbandry and farming were significantly associated with cchfv seropositivity .
vector ticks are generally present on the ground and on animals , which explains the risk for cchfv infection in persons who work in farming and animal husbandry .
personal protective measures such as regular examination of clothing and skin for ticks , tick removal , and use of repellents are important to prevent cchfv infection ( 12 ) .
we did not identify any association between seroprevalence and gender but found that cchfv seropositivity increased with age . in these regions of turkey , women contribute to farming and animal husbandry tasks and are exposed to ticks and livestock as often as men are .
however , age > 40 years was significantly associated with cchfv seropositivity and reflects the age of workers in turkish agricultural areas ( 4,8,13 ) . increased cchfv seroprevalence with age
exposure to blood and tissues of viremic animals during slaughter is a source of infection ( 12,14 ) .
however , we did not identify any association between cchfv seropositivity and contact with animals .
this finding may result from a low number of viremic animals in our study region .
it is known that domestic animals generally have low levels of viremia , which lasts a short time ( 15 ) .
however , in our study region , 79% of animals have been found to be seropositive against cchfv ( 4 ) . in the study population , 89 ( 11.4% )
persons had a history of close contact with a cchfv - infected patient . among these 89 persons , 14 ( 15.7% ) were seropositive , but this transmission route for cchfv was not statistically significant for our study population .
however , protection against this potential transmission route is especially important for healthcare workers in hospitals that provide care to cchfv case - patients ( 12 ) .
this study indicated that tick exposure is the most statistically significant transmission route for cchfv in a high - risk population in turkey .
effective tick prevention aids such as tick repellents may help reduce the risk . on the other hand , the absence of cchfv seropositivity in 87.2% of the population after 4 cchfv outbreaks in turkey may suggest that this population remains at risk for infection in the future .
 in the tokat and sivas provinces of turkey , the overall crimean - congo hemorrhagic fever virus ( cchfv ) seroprevalence was 12.8% among 782 members of a high - risk population . 
 cchfv seroprevalence was associated with history of tick bite or tick removal from animals , employment in animal husbandry or farming , and being > 40 years of age . 