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New research targets Mycoplasma genitalium
Results of a large national study of young men and women ages 18-27 suggest that Mycoplasma genitalium, a relatively new sexually transmitted infection, surpassed gonorrhea in prevalence.1 What is known about this infection, and what are possible treatments?
M. genitalium infection has been difficult to determine. It was first cultured in the early 1980s from the urethral exudates of two men with nongonococcal urethritis (NGU).2 M. genitalium is extremely difficult to grow in culture, so epidemiologic studies really can be done only using a nucleic acid amplification test, explains Lisa Manhart, PhD, MPH, assistant professor of epidemiology in the University of Washington School of Public Health and an investigator at the university's Center for AIDS and STD at Harborview Medical Center, both in Seattle. These tests are still "research-only" and so are not generally available to physicians and commercial laboratories, she states. No approved commercial assays have been made available, although investigators have presented information on kits for research use.3
The organism has been associated with several clinical syndromes, including NGU, pelvic inflammatory disease, and cervicitis, says Jennifer Ruth, a spokeswoman for the Centers for Disease Control and Prevention (CDC). With the recommended treatment for those syndromes, M. genitalium should be effectively treated, she notes. Current guidelines recommend azithromycin or doxycycline for the treatment for NGU.4
Research digs deeper
Scientists in Seattle looked at M. genitalium among men with urethritis in 2001 in an effort to identify causes of this syndrome. At that time, approximately 20%-50% of cases of male NGU had no identified pathogen other than chlamydia, Manhart observes. Results of the 2001 research determined that 22% of cases of nongonococcal urethritis were associated with M. genitalium.5 Since that time, the Seattle-based group of investigators has looked at M. genitalium in women, finding associations with cervicitis and endometritis.6,7
All of these studies were done in high-risk populations, such as sexually transmitted disease (STD) clinics or commercial sex workers, says Manhart. The current study was conducted in 1,714 women and 1,218 men between the ages of 18-27 who participated in Wave III of the National Longitudinal Study of Adolescent Health (Add Health), a nationally representative study. The Add Health study allowed researchers to look at M. genitalium in the general population, says Manhart, the lead investigator.
"While a representative population-based study is the most appropriate to estimate the prevalence of any infection in the general population, they are very expensive and difficult to conduct," observes Manhart. "We were very fortunate to be able to collaborate with the Add Health study, which is an extremely well-designed and well-conducted population based study."
When examining the prevalence of STDs within the study population, researchers found that the prevalence of M. genitalium was 1%, compared with 0.4%, 4.2%, and 2.3% for gonococcal, chlamydial, and trichomonal infections, respectively. No M. genitalium-positive individuals reported symptoms of discharge.1
What is the next step in research? Manhart's research team is conducting a randomized treatment trial among men with urethritis to determine which of the two most commonly recommended antibiotics — azithromycin and doxycycline — works best against M. genitalium in urethritis. The study is being conducted among men attending an urban STD clinic.
"We also are studying high-risk women in Kenya to determine if M. genitalium infection is associated with an increased risk of HIV transmission, as are other sexually transmitted infections such as gonorrhea and herpes simplex virus," notes Manhart. "Other members of our research group are looking at adverse pregnancy outcomes, such as preterm delivery."