Subclinical Infections with Crimean-Congo Hemorrhagic Fever Virus, Turkey - Vol. 18 No. 4 - April 2012 - Emerging Infectious Disease journal - CDC
Table of Contents
Volume 18, Number 4–April 2012
Volume 18, Number 4—April 2012
Dispatch
Subclinical Infections with Crimean-Congo Hemorrhagic Fever Virus, Turkey
Abstract
To investigate Crimean-Congo hemorrhagic fever virus in Turkey, we conducted a seroepidemiologic survey during January–April 2009. Seroprevalence of infection was 10% in a sample from an outbreak region and increased with patient age, indicating that the virus had been previously present in Turkey. We also estimated that 88% of infections were subclinical.The Study
Serum samples were tested for IgG against CCHFV at the Virology Reference Laboratory of the Refik Saydam National Public Health Agency, (Ankara, Turkey) by using a commercial ELISA kit (Vector-Best, Novosibrisk, Russia). Although the sensitivity and specificity of the kit were not specified by the manufacturer, studies that used this method have reported a sensitivity of 87%–98.3% and a specificity of 99%–100% (7,8). We defined subclincial cases as those in persons who were seropositive although they were not given a diagnosis or had not had severe symptoms compatible with CCHF at any time.
In addition, we compared information in our database with that in the database of reported cases at the Ministry of Health, Turkey. We used the χ2 test, t test, and Mann-Whitney U test for univariate statistical comparisons, as appropriate. Multivariable logistic regression was used to assess independent risk factors for seropositivity. We used the direct standardization method to adjust age-specific seropositivity rates for our study population with the age composition of the entire outbreak region. This adjustment enabled us to calculate expected numbers of infected (seropositive) persons in the outbreak region (Technical Appendix [PDF - 46 KB - 1 page]). Clinically diagnosed cases were compared with expected numbers of infections, and an observed:expected ratio was calculated.
The survey included 3,671 adults of whom 3,557 (97%) provided blood samples for serologic analysis. The mean ± SD age of the study population was 44.3 ± 16.2 years, the female:male ratio was 1.04 (51%:49%), and the most common occupation was farming (52.4%). Only 18.2% had a history of tick bite.
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