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Editor,—Trichomonas vaginalis infection occurs worldwide with an incidence of over 200 million infections per year.1 Clinical disease in women ranges from asymptomatic to severe vaginitis, and has been associated with preterm delivery2 and an increased rate of HIV-1 transmission.3
The magnitude of T vaginalis associated morbidity, including risk of HIV-1 transmission, makes simple accurate diagnosis important especially in at-risk populations. Microscopic examination of a wet mount vaginal specimen is easy to perform but only identifies 40–60%4 of infections in comparison to culture. The In-pouch culture system (Biomed Inc, San Jose, CA, USA) is reported to be equally sensitive yet more practical than traditional culture methods.5 If proved sensitive, culturing of urine from female patients for T vaginalis might prove useful in population based screening programmes, field investigations, or individual circumstances when a patient might not want a genital examination. Therefore, we set out to determine the sensitivity of culturing urine from women in comparison with a self collected vaginal swab for identification of T vaginalis.
We recruited subjects from a randomised community study that investigated the prevalence of sexually transmitted infections in women with and without access to female condoms.6 In this particular substudy we obtained specimens from participants in two study sites. Participants were instructed by one of the study nurses how to obtain a self collected vaginal swab and at the same time collect urine. Women were asked not to clean the genital area before providing both specimens. Immediately after collection the vaginal swab was inoculated into the In-pouch and urine was spun at 2000 g for 10 minutes. After the supernatant was discarded, the sediment was agitated and pipetted directly into the In-pouch. Specimens were shipped at room temperature to the University of Nairobi and incubated at 37°C for up to 5 days according to manufacturer's instructions. Daily microscopic examination was performed for identification of T vaginalis. Random specimen coding ensured that laboratory staff remained blind to specimen source and pairing.
We recruited 675 women for this substudy. T vaginalis was detected by culture in 121 (17.9%) women per self collected swab and 23 (3.4%) women per centrifuged urine. In comparison with culture of self collected swab, culture of centrifuged urine yielded a sensitivity of only 17% and a specificity of 99.6% (table 1). We originally intended to recruit over 2000 women into the study, but discontinued recruitment when preliminary results clearly demonstrated the inadequacy of urine for culturing T vaginalis in women.
In this large scale community study we found culture of centrifuged urine very insensitive for identification of trichomonads in women. Since only 5–10 organisms in a sample are necessary for a positive culture,5 these findings were unexpected. We cannot fully explain why culture of urine for T vaginalis in women proved so poor. Because of contamination of the external genitalia with vaginal fluid, a first void urine specimen might have proved a better sample.
Supported by the United States Agency for International Development, Family Health International and a grant from the National Institutes of Health (AI31448). Biomed Inc donated the In-pouch for this investigation.
Contributors: OAM helped design and oversee the study, assisted with analysis of the data, and drafted the manuscript; CRC designed the study protocol, analysed the data, and supervised preparation of the manuscript; DK assisted with the design and supervision of the study, and assisted with manuscript preparation; MK assisted with the design and supervision of the study, and assisted with manuscript preparation; JO performed the culture of T vaginalis, and assisted with manuscript preparation; JJB oversaw the laboratory aspects of the study, was co-principal investigator of the parent study, and assisted with manuscript preparation; MW was a co-investigator of the parent study and assisted in manuscript preparation; PJF was the principal investigator of the parent study and assisted with manuscript preparation.
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