Читать книгу Cases in Medical Microbiology and Infectious Diseases - Melissa B. Miller - Страница 48

CASE 5

This 26-year-old woman was referred to a public health clinic as a result of contact tracing in a case of gonorrhea. The woman, who had recently had unprotected sexual intercourse, had no symptoms. Physical examination was normal. Pelvic examination demonstrated a white vaginal discharge but was otherwise unremarkable. A cervical swab was obtained and submitted for Chlamydia trachomatis and Neisseria gonorrhoeae testing by a nucleic acid amplification test (NAAT). Examination of a wet mount of the vaginal discharge revealed the presence of a protozoan with a characteristic jerky motility. Figure 5.1 shows a Giemsa stain of the organism.

1 1. What organism did the wet preparation demonstrate? What other organism can cause vaginitis and can be detected by wet mount?

2 2. What other methodologies are available for detection of this organism?

3 3. How is infection with this organism most commonly acquired? What clinical presentations occur in women infected with this organism? In men infected with this organism?

4 4. This patient was asymptomatic when examined. She had had sexual contact with a partner who had a positive culture for N. gonorrhoeae. What would be appropriate antimicrobial therapy for this patient?

5 5. Why is infection with this organism of special concern in pregnant women? Would therapy be any different if this woman were pregnant?

6 6. What else should be done to prevent this patient from becoming reinfected with the organism identified on the wet preparation?

Figure 5.1

CASE 5 CASE DISCUSSION

1. The wet preparation demonstrated the trophozoites of the protozoan Trichomonas vaginalis. Examination of freshly prepared wet mounts of vaginal fluid, prostatic secretions, or urine from infected patients will reveal the organism in 40 to 80% of infected individuals. The organism is 7 to 23 μm in size, with a typical jerky motility. Microscopic examination for T. vaginalis is highly specific because its unique morphology makes it unlikely to be confused with any other organism that might typically be seen in genital tract secretions. Wet-mount examination is widely used by laboratories because it is inexpensive, rapid, easily performed, and requires relatively simple equipment (light microscope). However, because detection is based on motile live organisms, the test is best done in the clinic, unless a rapid transit time to the laboratory is possible. Trichomonads die quickly and test sensitivity declines sharply, making a specimen >15 minutes old of limited clinical value with this technique. Wet mounts can also be used to diagnose Candida vaginitis. In this form of vaginitis, yeast and pseudohyphae will be seen on wet mount. Candida vaginitis is frequently seen during or following antimicrobial therapy that alters the vaginal microbiota.

2. Rapid enzyme immunoassay (EIA), DNA hybridization, culture, and NAAT techniques have been developed to detect this organism. The most widely used rapid EIA test is an immunochromatographic “dipstick” test similar to a home pregnancy test. The test is performed on a vaginal swab. EIA is more sensitive than wet-mount examination and is more specific because of an objective colorimetric endpoint. Although more expensive than wet mount, EIA is relatively inexpensive compared to NAAT although not as sensitive.

A commercial DNA hybridization test is available that detects not only T. vaginalis but also other organisms associated with vaginitis (Gardnerella and Candida). Compared with wet mount and culture for Trichomonas, the hybridization test is 90% sensitive and 99% specific, but compared with NAAT it is only 63% sensitive.

Culture is done by growing the organism in enriched broth. A commercial test is available that uses a specially designed pouch that allows the direct examination of the broth microscopically for trophozoites. Culture is more sensitive than direct examination, but because of its complexity, expense, and length of time to result, it is primarily a research tool and is not commonly used clinically.

NAAT for T. vaginalis has been found to be more sensitive than direct examination, EIA, and DNA hybridization. It is both more rapid and more sensitive than culture. False-positive reactions with NAAT are of concern. A commercial NAAT was recently FDA-cleared which will likely promote more frequent clinical testing for this organism.

3. T. vaginalis is typically transmitted via sexual contact. Since Trichomonas infection is not a reportable disease, the number of cases that occur annually is unknown. However, it is estimated that 3 million women are infected annually in the United States, making this parasite an important health issue. Women can be asymptomatically infected, but most infections result in a vaginal discharge. Symptoms of itching or burning are frequently associated with this discharge. The infection can also involve the urethra, resulting in symptoms of dysuria. In men, most cases are asymptomatic, though some men have symptoms of urethral involvement, including a urethral discharge. Involvement of the prostate or seminal vesicles may occur as well. Confirming the diagnosis of T. vaginalis infection in men is difficult. Direct microscopic examination is insensitive and the EIA tests are not approved for use in specimens collected from males. The sensitivity of culture for men is low compared with the sensitivity of culture for infected women. Even NAAT may be falsely negative unless multiple specimens are tested. Further, an FDA-cleared NAAT is not currently available for use with male specimens.

4. Clearly, this woman must be treated for the T. vaginalis infection, the diagnosis having been established on the basis of a microscopic examination of her discharge. The drug of choice for this infection is metronidazole (Flagyl). It should be noted that there are an increasing number of reports of treatment failures due to metronidazole-resistant strains of T. vaginalis, though there are few studies on the surveillance of resistance. One study, published in 2006 from Birmingham, AL, tested clinical isolates of T. vaginalis and found that 17 of 178 (9.6%) were resistant in vitro. However, the laboratory results did not correlate well with the clinical response to treatment with metronidazole. Tinidazole has been approved for use to treat T. vaginalis. Clinical studies suggest that it is superior for the treatment of T. vaginalis in women, but there is a paucity of data on the effectiveness of this agent in T. vaginalis-infected men. Trichomonas-infected women who fail metronidazole therapy should be treated with tinidazole.

Even though this patient was asymptomatic, she was at a very high risk for a coinfection with N. gonorrhoeae because that organism had been detected in her male sexual partner. This finding prompted her visit to the clinic. Her presumptive gonococcal infection was treated with an intramuscular injection of ceftriaxone. In addition, since gonococcal infections are often associated with infection by C. trachomatis, she was given oral doxycycline. Her cervical swab NAAT was subsequently positive for both N. gonorrhoeae and C. trachomatis. Remember that patients can be simultaneously infected with multiple sexually transmitted infectious agents and that both C. trachomatis and N. gonorrhoeae more frequently cause asymptomatic infections in women than in men.

The patient was also offered testing for HIV infection. Recent studies have shown that T. vaginalis infection, as well as other sexually transmitted infections, increases the likelihood of HIV transmission.

5. T. vaginalis has been associated with preterm labor, premature rupture of membranes, and low-birth-weight babies. The use of metronidazole during pregnancy has been controversial because this drug has been shown to be mutagenic in bacteria and carcinogenic in laboratory animals. Retrospective studies have shown that women treated with metronidazole during pregnancy do not have a higher rate of delivery of children with birth defects than those women who did not receive this drug during pregnancy. Nevertheless, some experts would caution against using metronidazole during the first trimester.

6. The patient’s partner, who had been treated for gonorrhea and chlamydia, had not been treated for infection with T. vaginalis. As with other sexually transmitted infections, treatment of both people within a sexual relationship is necessary to prevent reinfection by the untreated person. Treatment of only the person presenting and not the partner can result in a “ping-pong ball” phenomenon, where the infection “bounces” back and forth between the two partners. In addition, the patient was advised on the risks of unprotected sex and informed that condom use may help to prevent disease transmission.

REFERENCES

1. Andrea SB, Chapin KC. 2011. Comparison of Aptima Trichomonas vaginalis transcription-mediated amplification assay and BD Affirm VPIII for detection of T. vaginalis in symptomatic women: performance parameters and epidemiological implications. J Clin Microbiol 49:866–869.

2. Hobbs MM, Lapple DM, Lawing LF, Schwebke JR, Cohen MS, Swygard H, Atashili J, Leone PA, Miller WC, Seña AC. 2006. Methods for detection of Trichomonas vaginalis in the male partners of infected women: implications for control of trichomoniasis. J Clin Microbiol 44:3994–3999.

3. Schwebke JR, Barrientes FJ. 2006. Prevalence of Trichomonas vaginalis isolates with resistance to metronidazole and tinidazole. Antimicrob Agents Chemother 50:4209–4210.

4. Schwebke JR, Burgess D. 2004. Trichomoniasis. Clin Microbiol Rev 17:794–803.

5. Sutton M, Sternberg M, Koumans EH, McQuillan G, Berman S, Markowitz L. 2007. The prevalence of Trichomonas vaginalis infection among reproductive-age women in the United States, 2001–2004. Clin Infect Dis 45:1319–1326.

6. Van der Pol B. 2007. Trichomonas vaginalis infection: the most prevalent nonviral sexually transmitted infection receives the least public health attention. Clin Infect Dis 44:23–25.