Commercially available home tests for chlamydia could be failing to identify between 75% and 83% of people infected when compared with the “gold standard” biochemical lab test, according to new research from the Netherlands.
The study of 772 women found that three “point of care” tests available on the internet and in pharmacies only correctly identified 17-25% of women who had chlamydia according to nucleic acid amplification testing commonly used by GPs and sexual health clinics.
Chlamydia is the most common sexually transmitted infection in the United Kingdom. More than 200,000 people were diagnosed in 2009, the majority of whom were aged 15-24. Around 50% of men and 70-80% of women who get chlamydia will have no symptoms, yet left undiagnosed chlamydia cause infertility.
Point of care tests for chlamydia usually involve the woman taking a vaginal swab herself and sending the sample to a laboratory to be tested, then going for an appointment with her doctor to get the result. Currently testing involves one doctor’s appointment to have a sample taken and a second 1-2 weeks to get the result, which is a much more time consuming approach.
The authors of this study assessed all women over the age of 16 who applied for a consultation at a sexual health clinic in Maastricht between September 2007 and April 2008. A total of 772 women with a median age of 23 were included in the final study.
When nucleic acid amplification testing was used, 11% of these women were found to be infected with Chlamydia trachomatis.
The authors then assessed whether three tests commercially available and certified in Europe – Handilab-C, Biorapid CHLAMYDIA Ag test, and QuickVue Chlamydia test – could identify which women had chlamydia.
The three tests only picked up 17.1-25.0% of women who had chlamydia (sensitivity) and correctly excluded 93.7-99.7% of those who didn’t (specificity). World Health Organization criteria indicate that point of care tests should have a sensitivity of between 43% and 65% and a specificity of 98%.
The sensitivity of two of the tests improved slightly if they were performed within 72 hours of the women taking a vaginal swab. As little as 19.8% of women who tested positive actually had chlamydia, although about 90% of those who tested negative were free from disease.
The results of this study indicate that many infections would have been missed had these point of care tests been used on their own, allowing women to go untreated and potentially spread the infection, and people with false positive results could have been treated unnecessarily.
On this basis the authors state: “In our opinion, the chlamydia point of care tests we have evaluated are not ready for widespread use.”
In an editorial on the topic, Dr Sue Skidmore from the Department of Microbiology at Princess Royal Hospital, Telford, agrees. “It is widely agreed that rapid tests for sexually transmitted infections with high sensitivity and specificity would provide advantages,” she writes, “although the introduction of their use, particularly for home use, needs to be rigorously evaluated and controlled with an assurance that robust quality assurance is in place when appropriate.”
van Dommelen L et al. (2010) Alarmingly poor performance in Chlamydia trachomatis point-of-care testing. Sexually Transmitted Infections 86:355-359. DOI: 10.1136/sti.2010.042598