Mycoplasma genitalium Incidence, Organism Load, and Treatment Failure in a Cohort of Young Australian Women

Background. Mycoplasma genitalium (MG) is an emerging sexually transmitted infection (STI) that is potentially associated with reproductive tract sequelae in women. This study aimed to estimate MG incidence and treatment failure and provide estimates of organism load in infection. Methods. 1110 women aged 16-25 years were recruited from primary care clinics in Australia. Women were tested for MG at baseline, 6 months, and 12 months, and MG organism load was measured by quantitative polymerase chain reaction (PCR). MG-positive cases were screened for MG 23S ribosomal RNA (rRNA) gene point mutations shown to confer azithromycin resistance using high-resolution melt following PCR. Results. MG incidence rate was 1.3 per 100 person-years (n = 14; 95% confidence interval [CI], .8-2.3); women reporting 3 or more sex partners in the last 12 months had an increased rate of incident infection (rate ratio [RR], 5.1; 95% CI, 1.3-19.6]). There were 3 cases of MG reinfection (0.8 per 100 person-years [95% CI, .1-.9]. Organism load was higher for prevalent than incident infection (P = .04). There were 3 cases of treatment failure (9.4% [95% CI, 2.0-25.0]); organism load was higher in cases with treatment failure than in successfully treated cases (P < .01). An MG 23S rRNA mutation was detected in 5 cases (3 cases of treatment failure and 2 successfully treated). Conclusions. Although MG incidence was relatively low, testing should be recommended for women considered to be at increased risk based on sexual history. Our results also suggest that organism load might be important in azithromycin treatment failure.