This is the first study to report the prevalence of C. trachomatis
infection in a former Soviet Union country. The observed prevalence was 5.2% among participants of 18–35 years, which is consistent with the results presented from the neighbouring European countries. Lowet al.14
reported 3.2% prevalence of chlamydia in a study implementing home-testing and randomly selected participants from the urban general practitioner practices (UK). Andersen et al.15
from Denmark reported prevalence of 6.5% among women and 5.9% among men aged 21–23 years, randomly selected from the county’s health service register and invited to submit home-obtained samples via mail.
This study had several limitations. While the cross-sectional study design does not allow us to establish a causal relationship, our goal was to estimate prevalence and factors related to prevalence. The degree to which the study is representative of the larger population is influenced by the low response rate and potential selective factors associated with response. However, this response rate was similar to that seen in recent studies.14,15,18
To evaluate the effect of selection bias, we collected demographic information from all non-respondents. The probability of not responding was greater for men, a phenomenon described in several previous studies. A second limitation was the fact that a sizable proportion of female study participants had current urogenital symptoms, and those who responded may have done so because they were explicitly seeking chlamydia testing for an extant symptomatic condition. Thus, the prevalence of chlamydia reported here may over-represent the true rate of infection in the source population. The association between chlamydial infection and symptoms suggests that home-sampling may well serve as opportunistic screening. An issue to be considered in screening studies is the use and possible abuse of screening tests. In low-prevalence settings, even excellent tests have poor positive predictive value.19
To minimize the likelihood of a false-positive, a positive NAAT test was based on double-testing for C. trachomatis
using two different NAAT tests (primers). Thus, while it is reasonable to assume that the prevalence estimates from this study are somewhat inflated because of selective participation, the estimate is likely better than that based on traditional surveillance data. Finally, the sample size was insufficient for further stratification.
In European countries, genital chlamydial infection is now among the most commonly diagnosed bacterial STI, and this diagnosis has been on the rise since the mid-1990s.1
Both surveillance and clinical case notification data suggest a disproportionate disease burden among women in Estonia, as well as in many other countries.1,9
However, opportunistic screening often introduces bias in the data collected by national passive surveillance and clinical case notification systems. Recent population-based surveys in Scandinavia, the UK and the USA have consistently shown similar prevalence of chlamydia among heterosexual men and women.14,15,20
Men are an important reservoir of infection for women, and men also suffer health consequences from chlamydial infection.21
As such, men should also be targeted for chlamydial screening and treatment. Recently, in the USA, the CDC has recommended chlamydial screening for specific higher risk groups of men.22
Pinpointing target groups for chlamydial screening remains a challenge. Most infected individuals are asymptomatic. Population-based studies to identify risk factors for chlamydia have not identified specific factors, other than young age, that would more efficiently target screening. The majority of our study participants had consulted their family physician within the last 12 months of the study. Family-physician practices could thus provide good opportunistic screening access for both men and women. A strategy of using mailed samples as an adjunct to screening during health visits may enhance access to STI testing. As also suggested by earlier studies14
mixed models of chlamydial screening, such as specimen collection by a health-care provider or self-obtained, and active or opportunistic screening should be evaluated to determine which model delivers consistently higher uptake than either alone. Effective methods for identifying and treating those who are infected with chlamydia need to be developed and evaluated in Estonia and similar countries.