Regional Laboratory
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VOLUME 2 ISSUE 8 SEPTEMBER 1997
Vaginal Trichomoniasis is a common sexually transmitted urogenital disease caused by the protozoan, Trichomonas vaginalis. Transfer of infection is usually due to direct contact between sexual partners. Signs and symptoms of Trichomonal vaginitis include foul-smelling discharge, punctate hemorrhagic vaginal lesions, “strawberry cervix”, urinary frequency, and dysuria. Urogenital infections with Trichomonas in men are usually asymptomatic, but may cause urethral discharge. Diagnosis of vaginal Trichomoniasis is most easily accomplished by identification of the wiggling trophozoites in wet mount smears prepared from a cervicovaginal swab. Immediately after obtaining the cervicovaginal swab, the swab should be placed in saline. It can then be sent directly to the lab for preparation of the wet mount smear, followed by microscopic examination by the laboratory technician. Alternatively, a smear can be prepared at the bedside from the saline-soaked swab, coverslipped, and immediately examined microscopically by the clinician or clinician’s assistant. The trophozoites are delicate, and do not survive long on the wet mount slide, especially as drying occurs. For this reason, the wet mount must be examined microscopically fairly soon after preparation of the slide. Sensitivity of this method varies from 49% to 80%. Sensitivity can be increased by considering additional clues that are often associated with Trichomonas infection, including presence of large numbers of neutrophils, presence of coccoid bacteria and/or Leptothrix, specimen pH above the normal level of 4.5, and presence of an amine odor. In addition, wet mounts from the ectocervix or vaginal pool are more sensitive for Trichomonas than wet mounts obtained from the endocervix.
Alternative methods of diagnosis of vaginal Trichomoniasis include 1) identification of the trophozoites on Pap smears, 2) vaginal pool culture, or 3) DNA probe tests. The sensitivity of Pap smears for Trichomonas infection is 60-70%, and some studies show only 70% specificity. Dense neutrophilic inflammation should prompt the screener to look closely for Trichomonas. When Trichomonas is reported on a screening Pap smear from an asymptomatic patient, a confirmatory test (wet mount or culture) should be performed prior to initiating therapy.
Vaginal pool culture for Trichomonas is regarded as the most sensitive technique (85-95%). Culture requires innoculation of special culture medium (Diamond’s medium) fairly soon after obtaining the specimen while organisms are still viable. Cultures may be obviously positive at 24 hours, but can require up to 3-5 days for completion. Trichomonas culture can be used in patients with suspected infection who have a negative wet mount. It should be performed in cases of sexual abuse where vaginal penetration is suspected regardless of whether the wet mount is positive or negative. Trichomonas vaginalis is the third most common sexual pathogen seen in sexually abused children, but it must be kept in mind that the potential for non-sexual transmission does exist.
DNA probes for Trichomonas are available, but are also more expensive than wet mount; in general, their sensitivity is around 85%, with 98% specificity. A fairly recent DNA direct probe test (Affirm VP III, Becton Dickinson) combines testing a single specimen for Trichomonas, Gardnerella and Candida, and results are available in less than one hour. The sensitivity for Trichomonas with Affirm VP III is much better than wet mount at 92%, and specificity is 99.7%.
Serologic studies for antibodies to Trichomonas lack sensitivity and specificity, and currently have no role in the evaluation of the individual patient.
Implications of Trichomonal Vaginitis:
Trichomonal vaginitis has been associated with other cervicovaginal pathology, including concomitant infection with Chlamydia trachomatis, Herpes simplex virus, and Neisseria gonorrhoeae. The incidence of cervical intraepithelial neoplasia (CIN) is higher in women with Trichomonas infection than in those without infection. Approximately 20% of heterosexual male sexual partners of women with Trichomonal vaginitis are also infected, and should be examined, and if found to be carriers, should also be treated.
Treatment of Trichomonas Infection
A single 2-gram dose of metronidazole is recommended for both women and men with Trichomoniasis. This therapy has been found to be highly efficacious, and is less toxic and less expensive than other regimens. Importantly, it eliminates the problem of patient non-compliance. The main disadvantage of the single dose regimen is that of higher reinfection if sexual partners are not treated simultaneously. Alternative regimens call for one week of therapy using 250 mg of metronidazole three times daily or 500 mg twice daily. The 7-day course may minimize the risk of re-infection by protecting the patient long enough for sexual partners to obtain treatment. Prepubertal girls with Trichomoniasis should be treated with a single dose of 40 mg/kg (maximum 2 grams), or with a regimen of 15 mg/kg/day in three divided doses (maximum daily dose 2 grams) for 7 days. Asymptomatic infected women should be treated as a public health measure, to decrease the reservoir for this disease. Side effects of metronidazole include mild nausea or bad taste, and intolerance of alcohol. Metronidazole is contraindicated in the first trimester of pregnancy, and should be avoided if possible throughout pregnancy. Symptomatic pregnant women in the first trimester should be treated with 100 mg clotrimazole vaginal tablets at bedtime for 1-2 weeks. This cures only about 20% of patients, but symptoms may be controlled adequately until later in the pregnancy when more definitive therapy can be used. Women remaining infected should be treated prior to delivery to avoid transmission to the newborn.
Trichomonal resistance to metronidazole has been observed, and seems to be increasing. Antimicrobial sensitivity testing of T. vaginalis has not been standardized, and the level of resistance depends markedly on assay conditions. Treatment of apparent resistant infection may be accomplished using 2 grams of oral metranidozole daily for 3-7 days. More resistant infections may require 2 grams/day for 7-14 days. In both of these regimens, adjunctive topical medication should be utilized. Rarely, intravenous metronidazole may be needed.
References:
“Accuracy of the Papanicolaou smear in the Diagnosis of Asymptomatic infection with Trichomonas vaginalis.” M. W. Weinberger and J. H. Harger. Obstetrics and Gynecology. 1993, Sept.; 82(3): 425-9.
“Evaluation of Affirm VP Microbial identification Test for Gardnerella vaginalis and Trichomonas vaginalis.” Briselden, A.M. and Hillier, S.L. Journal of Clinical Micro-biology. 1994, January; 32(1): 148-52.
Mandell, Douglas and Benett’s Principles and Practice of Infectious Diseases. Edited by Gerald L Mandell, M.D., John E. Bennet, M.D. and Raphael Dolin, M.D. Churchill Livingstone, Fourth Edition. New York, 1995: pp. 2,493-6.
“Office Laboratory Diagnosis of Vaginitis. Clinician-performed Tests Compared With a Rapid Nucleic Acid Hybridization Test.” D. G. Ferris, et al. Journal of Family Practice: 1995, Dec.; 41(6): 575-81.
“Sexually Transmitted Diseases in Children and Evidence of Sexual Abuse.” A.C. Argent, et al. Child Abuse and Negligence. 1995, October;19(10): 1303-10.
“Trichomonas vaginalis (TV) and Human Papillomavirus Infection (HPV) and the incidence of Cervical Intraepithelial Neoplasia (CIN) grade III.” I.T. Gram, et al. Cancer Causes and Control. 1992, May; 3(3): 231-6.
“Update on Laboratory Diagnosis of Sexually Transmitted Diseases.” Gail L. Woods, M.D. Clinics in Laboratory Medicine. 1995 Sept. 15(3): 665-84.