Over the past 200 years, identification of the specific organism causing an infection has evolved from a reliance on patient history and physical examination to the use of microscopic examination of relevant biological samples to the rise of microbial culture and immunological testing as the gold standards for diagnosis. More recently, advances in nucleic acid testing have made nucleic acid amplification testing (NAAT) a primary method for identifying the specific organism causing an infection.
The evolution of the diagnosis of gonorrhea in clinical practice is a good example of the inexorable evolution of diagnostic techniques from physical examination to microscopic analysis to culture and finally to NAAT. Neiseer discovered Neisseria gonorrhea in 1879.1 In 19th century general medical practice gonorrhea was often diagnosed based on history and physical examination and sometimes microscopy was also utilized.2 In the mid-20th century, it was realized that culture was a superior approach to diagnosis of gonorrhea, and it became the gold standard for diagnosis in general practice.3 NAAT has now replaced culture as the gold standard for the diagnosis of gonorrhea because of its superior performance in clinical practice.4 It may now be time to consider using NAAT rather than microscopy and culture in general practice for the identification of specific microorganisms causing vaginitis.
Trichomoniasis
Vaginitis caused by Trichomonas vaginalis is characterized by a discharge that is foamy and green-yellow in color, with a vaginal pH that is >4.5. Microscopy of a vaginal specimen has low sensitivity, in the range of 50%, for detecting T vaginalis.5-7 There are many factors that make microscopy a poor approach to the diagnosis of T vaginalis, including the rapid decrease in protozoan motility once a vaginal specimen is placed on a glass slide and the similar size of non-motile T vaginalis and other cells in the vagina.
Given the low sensitivity of microscopy for the diagnosis of trichomoniasis, the American College of Obstetricians and Gynecologists (ACOG) recommends NAAT as a primary approach to test for T vaginalis, with culture or NAAT testing as alternative approaches.8 The Centers for Disease Control and Prevention (CDC) recommends that if a wet mount is negative for T vaginalis that NAAT should be utilized.9
In this 2-step testing process, the first step is to test the vaginal pH and perform a microscopic examination of a vaginal specimen for T vaginalis. If T vaginalis organisms are detected, the diagnosis of trichomoniasis is confirmed. If organisms are not detected the second step would be to send a vaginal or urine specimen for NAAT for T vaginalis or for culture. An advantage of NAAT over culture is that urine specimens can be used for diagnosis of T vaginalis while urine specimens are not suitable for culture because of low sensitivity. For patients diagnosed with trichomoniasis, the CDC recommends that testing be repeated in 3 months because of high rates of reinfection. NAAT would be an optimal test to use in this situation.
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