Trends in adult chlamydia and gonorrhoea prevalence, incidence and urethral discharge case reporting in Mongolia from 1995 to 2016 – estimates using the Spectrum-STI model

Objective: To estimate Mongolia’s prevalence and incidence trends of gonorrhea and chlamydia in women and men 15-49 years-old, to inform control of STIs and HIV, a national health sector priority. Methods: We applied the Spectrum-STI estimation model, fitting data from two national population surveys (2001 and 2008) and from routine gonorrhea screening of pregnant women in antenatal care (1997-2016), adjusted for diagnostic test performance, male/female differences and missing high-risk populations. Prevalence and incidence estimates were then used to assess completeness of national case reporting. Results: Gonorrhea prevalence was estimated at 3.3% (95% confidence interval, 1.6-3.9%) in women and 2.9% (1.3-3.4%) in men in 2016; chlamydia prevalences were 19.5% (17.3-21.9%) and 15.6% (13.8-17.5%). Corresponding new incident cases in women and men in 2016 totaled 60,334 (36,147-121,933) and 76,893 (40,428-267,884) for gonorrhea, and 131,306 (84,232-254,316) and 148,162 (72,145-444,110) for chlamydia. Gonorrhea and chlamydia prevalence declined by an estimated 33% and 11%, respectively, over 2001-2016. Comparing numbers of symptomatic and treated cases estimated by Spectrum with gonorrhea case reports suggests that 15% of symptomatic treated gonorrhea cases were reported in 2016; only a minority of chlamydia episodes were reported as urethral discharge cases. Discussion: Gonorrhea and chlamydia prevalence are estimated to have declined in Mongolia during the early 2000s, possibly associated with syndromic management in primary care facilities and improving treatment coverage since 2001, and scale-up of (Global Fund-supported) HIV/STI prevention interventions since 2003. However, prevalence remain high, with most gonorrhea and chlamydia cases not treated or recorded in the public health system.