Objective: In Japan it was reported that about 9% of sexually active female teenagers had Chlamydia trachomatis. Most of them were asymptomatic, which may lead to continuing spread of the infection. Like C trachomatis, Mycoplasma genitalium is a pathogen in male non-gonococcal urethritis. However, few studies of the prevalence of M genitalium in the general population have been reported. The objective of this study was to determine the prevalence of M genitalium infection among younger females and to determine risk factors for this infection.
Methods: The study was conducted between October 2005 and January 2006 using first voided urine specimens and questionnaires from female students of three vocational schools in the Miyazaki prefecture, Japan. C trachomatis was detected with Amplicor™ PCR. M genitalium was detected with inhibitor controlled real-time TaqMan™ PCR detecting the MgPa adhesion gene and with a PCR detecting the 16S rRNA. Risk factors associated with infection of M genitalium or C trachomatis were analysed with Fisher’s exact test.
Results: Among 298 female, 249 (84%) had had experience of sexual intercourse. The prevalence of M genitalium was 2.8% (95% CI 0.76% to 4.86%) and the prevalence of C trachomatis was 8.8% (95% CI 5.31% to 12.36%).
Conclusions: The risk factors of infection with M genitalium were more than five lifetime sexual partners and co-infection with C trachomatis.
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In Japan it has been reported that about 9% of sexually active female teenagers had Chlamydia trachomatis.1 Most of them were asymptomatic, which may lead to continuing spread of the infection. Like C trachomatis, Mycoplasma genitalium is a cause of male non-gonococcal urethritis (NGU). In our previous study, M genitalium was detected from about 17% of males with NGU or from 25% of males with non-chlamydial NGU.2 In these male patients with urethritis, half of them were not infected by commercial sex workers. Furthermore, asymptomatic carriage could possibly lead to pelvic inflammatory disease in the women. In two Japanese studies, the prevalence rates of M genitalium were reported to be 0.8% among pregnant females3 and 1% commercial sex workers.4 The objective of this study was to determine the prevalence of M genitalium infection among younger females and to determine risk factors for this infection.
This study was conducted between October 2005 and January 2006. Urine specimens and questionnaires were collected from female students in three vocational schools in the Miyazaki prefecture, Japan. Following an educational lecture on sexually transmitted infections (STI) and birth control, the students received oral information about the survey design and self collection of specimens and questionnaires. Each student collected about 10 ml of first voided urine (FVU) after getting up in the morning and brought it with the questionnaire to school. The items in the questionnaire are shown in table 1. Information was collected concerning age, history of genital symptoms (yes or no), history of STI (yes or no), number of lifetime partners (1, 2, 3, 4 and ⩾5), age at first intercourse (⩽16, 17, 18 and ⩾19 years), sexual partners in the previous 6 months (none, 1 and ⩾2), new partner in the previous 6 months (yes or no) and condom use (not always or always).
The urine specimens were transported in cooling bags to the laboratory of Mitsubishi Chemical BCL, Tokyo, Japan, for analysis of C trachomatis with Amplicor™ PCR (Roche Molecular Systems, Branchburg, NJ, USA) according to the manufacturer’s instruction. After the analysis of C trachomatis, specimens were transported frozen to the first author’s laboratory for analysis of M genitalium. The M genitalium was detected by inhibitor controlled real-time TaqMan™ PCR using primers detecting the M genitalium MgPa adhesion gene.5 All positive results were confirmed by a PCR detecting the 16S rRNA gene of M genitalium.6
Risk factors associated with M genitalium or C trachomatis infections were analysed with Fisher’s exact test as the groups were too small to permit analysis with logistic regression.
A total of 298 women submitted both urine specimens and completed questionnaires; 249 (84%) students had had sexual intercourse. The median age of the participants was 20 (range: 18–45) years. The prevalence of M genitalium was 2.8% (95% confidence interval (CI) 0.76% to 4.86%) and the corresponding prevalence of C trachomatis was 8.8% (95% CI 5.31% to 12.36%). Three students had dual infections with M genitalium and C trachomatis. The median DNA load of M genitalium was 6252 (range: 95–26590) genomes/ml.
Risk factors for infection with M genitalium or C trachomatis are shown in table 1. All M genitalium PCR positive students had more than five lifetime sexual partners. In addition, having a positive C trachomatis test was a risk factor for M genitalium infection. For C trachomatis infection, more than three lifetime partners and more than one partner within the previous 6 months were identified as risk factors.
DISCUSSION AND CONCLUSIONS
Previous reports on the prevalence of M genitalium in population-based studies of females have found slightly different prevalences.7–9 Our result was almost identical to that from Denmark7 whereas only 1% were positive in a US study.8 Our study was not a true population-based study as we screened for M genitalium in asymptomatic, educated females. However, the confidence intervals between our study and these previous population-based studies were overlapping.
For screening, important factors are the type of specimen as well as the method used for detection. For males, FVU is a common specimen for screening urethritis pathogens. For females, Jensen compared three types of female genital specimens, including FVU, cervical swabs and urethral swabs, and found that FVU specimens were more efficient than swabs.10 PCR inhibition was not different between the three types of specimens. To evaluate if differences in PCR methods could explain the lower prevalence found in other Japanese studies, six of the seven M genitalium PCR-positive urine specimens from this study were re-examined by hybridisation-based microtiterplate assay described by Yoshida et al11 at the laboratory of Mitsubishi Chemical BCL, but two specimens with 95 or 253 genomes/ml of M genitalium were negative. This result suggested that there were some differences in the sensitivity for detecting M genitalium from female urine specimens.
Two risk factors for M genitalium infection were identified: these were more than five lifetime partners and co-infection with C trachomatis, indicating sexual transmission. The number of participants in our study was too small to allow a more detailed analysis. However, co-infection with C trachomatis could also be a marker for multiple partners and unprotected sex. If the selection criterion of more than five lifetime partners was applied in a screening algorithm, a prevalence of 2.8% might be considered high enough to warrant screening. However, further studies proving that M genitalium infection causes sequelae are needed to justify this.
Mycoplasma genitalium is a sexually transmitted infection.
Prevalence of M genitalium in Japanese asymptomatic younger women was 2.8%.
Risk factors for infection with M genitalium in younger females were more than five sexual partners and co-infection with C trachomatis indicating sexual transmission.
Competing interests: None.
Ethics approval: This study was approved by the ethics committee of the University of Miyazaki, Japan.
Patient consent: Informed consent was obtained in writing from each student.
Contributors: RH initiated the study, collected samples and questionnaire data, was responsible for analysis of samples for M genitalium, participated in data analysis and wrote the first draft of the manuscript. HI participated in planning of the study and collecting of samples and questionnaire data. HT performed the statistical analysis of data and edited the manuscript. JSJ participated in study design and edited the manuscript. YO provided his grant for this study and edited the manuscript.
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