WASHINGTON -- Diagnosis and treatment of trichomoniasis can be tricky, Dr. Anne Rompalo said at an update on sexually transmitted diseases sponsored by OB.GYN. NEWS and Boston University.
"We think we know a lot about trichomonas, but we really don't," said Dr. Rompalo of Johns Hopkins University, Baltimore. Approximately 170 million new cases of trichomoniasis are believed to occur worldwide each year, with about 8 million in North America. Its incidence is second only to chlamydia among nonviral STDs, with as many as one in four sexually active individuals becoming infected with trichomonas at some point in their lives.
Congenital trichomonas has not been documented, and the parasite is not believed to be transmitted by fomites. However, there has been at least one credible case report of a virgin becoming infected via a hot tub. "I never say never," Dr. Rompalo remarked.
Unlike chlamydia, which tends to infect adolescents and younger women, trichomonas appears to be more evenly distributed among sexually active women of all ages. It is often seen with gonococcal infections and bacterial vaginosis, yet it is not clear whether the presence of trichomonas itself is a marker for high-risk sexual behavior, she said.
Indeed, while Trichomonas vaginalis is the only species that attacks the genitourinary tract, there are two others that can infect humans: T. tenax, found in the mouth, and Pentatrichomonas hominis, found in the intestine. It may be that some positive trichomonas cultures found in urine samples may actually be another non-STD species, something to consider when such a result is found in an unlikely STD candidate, she remarked.
In women, the disease often--although not always--presents with a diffuse, malodorous, yellow-green discharge with vulvar irritation. Symptoms include itching, burning, and a frothy discharge that worsens after menses. But some women are asymptomatic.
Although approximately two-thirds of male sexual partners of infected women will develop urethral colonization, men rapidly clear the organism. However, some men present with nongonococcal urethritis.
Diagnosis is usually made by microscopy of vaginal secretions. The organism is about the size of a white blood cell (approximately 10-20 [micro]m wide) and is ovoid, with flagella that make a distinctive, jerky movement that can be dearly seen on a wet preparation slide, Dr. Rompalo said.
But microscopy isn't very sensitive. In a recent study of 337 women by Dr. Rompalo and her associates, wet preparation was just 52% sensitive, compared with 78% for culture and 84% for polymerase chain reaction, which is not currently commercially available. Use of polymerase chain reaction would have resulted in treatment of additional patients, the authors said (Clin. Infect. Dis. 35:576-80, 2002).
"We're not doing really badly with clinical diagnosis and our current therapeutic algorithm, but we need better tests in order to eradicate trichomoniasis," Dr. Rompalo remarked.
A wider range of treatment options would likely be helpful as well, since only one, metronidazole, is currently available in the United States. The two recommended regimens--either a single oral 2 g dose or 500 mg twice daily for 7 days--are 92%-95% effective. Ensuring treatment of sex partners might improve that cure rate, but trying to do that with an asymptomatic male can be a challenge, she noted.
Metronidazole resistance, while generally low and not common (approximately 5%), has been reported as increasing in some areas of the world. High-level resistance occurs in about 1 in every 2,000-3,000 cases, "but we still worry about it," she said.
Low-level resistance in women can be treated with increasing doses of metronidazole (total dose range 20-40 g). Optimal doses for men are not known.
High-level resistance, on the other hand, is a challenge. One recent study suggested that a combination of oral and intra-vaginal tinidazole is effective and highly tolerable in women with refractory trichomonas (Clin Infect. Dis. 33:1341-46, 2001). But right now tinidazole is only available in the United States for compassionate use.
The Centers for Disease Control and Prevention does not recommend follow-up for men and women who become asymptomatic. If the infection is still present, however, the first step is to ensure that the partner has been treated, Dr. Rompalo emphasized.
For treatment failure, the CDC recommends retreating with 500 mg metronidazole twice daily for 7 days. If failure occurs again, use a single 2-g dose once a day for 3-5 days. The third time, call the CDC at 770-488-4115 to help determine whether you're dealing with a resistant strain. In the meantime, patients must be told to avoid sex until both partners are cured and asymptomatic. Again, this may not be easy, she said.
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