Literature review > Issue_3 > Review Oakeshott et al. 

Perinatal transmission of Chlamydia trachomatis infection can result in debilitating consequences in the newborn. Prenatal screening and treatment may help to reduce such transmission [1]. However, local prevalence data based on surveys in the community are required to assess the need to screen pregnant women for this infection.

Several studies have shown that women below 25 yrs are at increased risk of chlamydial infection. This age group could be a target population for screening. There is also the issue of choosing the most appropriate method of sample collection and testing. Reliable self-collected samples will greatly help in the process. Other logistic issues like transport and storage of samples also should be considered before initiating nation-wide screening programmes.

This report addresses two main issues related to screening of pregnant women i.e., the prevalence of infection in the community, and the value of self collected samples for identifying C. trachomatis infection by ligase chain reaction (LCR, Abbott Diagnostics, Maidenhead). Previous data have shown that nucleic acid amplification tests are suited for field screening of sexually transmitted infections in areas of low prevalence and that self collected swabs and urine are suitable samples for testing [2]. However, performance of these methods has not been previously tested in early pregnancy in community practice in the UK.

In this study, which involved general practice and family planning clinics in South London, the prevalence of infection in newly pregnant women was determined as 2.4% (95% CI; 1.5 -3.3). This is similar to those reported earlier. However, as the authors themselves point out, these rates have to be treated with caution. The study included only women who presented before 10 wks of gestation. Similarly, those intending to have pregnancy termination were excluded. Women who book late for antenatal care and those who seek termination may have different risks for infection and thus, this study may have excluded several women at possibly higher risk of infection. No further information is available on the characteristics of these women who were excluded.

This study also confirms that targeting women in the lower age group for screening is likely to be beneficial. Below 25 yrs of age, 8.6% (95% CI; 4.1 -12.9) of the women were infected.

Self-administered vaginal swabs and first-pass urine samples were also evaluated for performance in a community setting. Both specimens of adequate quality were obtained from 95% of the women, indicating that self-collected samples are reliable. Although approximately 50% of women preferred to collect urine, all were willing to collect a vaginal swab, which had a better sensitivity, in this study. A method for storage and transport of samples from general practice is also described.

Information on how this system compares with conventional methods of collection, transport, and testing would have added more meaning to the evaluation. It will also be useful to have data on predictive values if only LCR is used for screening. Information on cost involved is also lacking.

Similar studies may need to be repeated in different geographic areas to identify the target populations for screening and also methods for sample collection and testing. Even with targeting the population, screening for C. trachomatis can be labour-intensive and expensive. However, introduction of such interventions may prove to be beneficial in the long run.

References:

1. CDC. Sexually transmitted diseases treatment guidelines 2002. Centers for Disease Control and Prevention. MMWR Recomm Rep 2002; 51: 1-78.

2. Watson EJ, Templeton A, Russell I et al. The accuracy and efficacy of screening tests for Chlamydia trachomatis: a systematic review. J Med Microbiol 2002; 51: 1021-31.

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