Prevalence and risk factors of chlamydia, gonorrhoea and syphilis infection in Hong Kong : a population-based geospatial household survey and testing

Abstract

Sexually transmitted infections (STIs) such as chlamydia, gonorrhoea and syphilis cause serious health consequences including infertility, pelvic inflammatory disease, and increase HIV infection risks. Population-based studies provide essential information for effective control and prevention. In Hong Kong, there are limited data on STI prevalence and no STIs are notifiable except hepatitis B. This study aimed to investigate the prevalence and correlates of these three STIs amongst 18-49-year-old Hong Kong residents. Seventy-nine District Council Constituency Areas (DCCAs) were randomly selected from 412 DCCAs in 18 districts of Hong Kong. These were primary sampling units, with the chance of selection proportional to the population sizes of the districts. Residential buildings and units were randomly drawn using geospatial software. Invitation letters were sent to selected households before interviewers’ visits to recruit one eligible subject per household. A questionnaire on sexual practice and health was conducted. Polymerase chain reaction was used to test urine samples for chlamydia and gonorrhoea with optional point-of-care syphilis testing. Prevalence data were weighted according to the 2011 Census, and risk factors were identified through logistic regression. Among 881 participants (response rate of 24.5%), the overall prevalence of composite STIs was 1.9%(95%CI: 1.2-2.9), with 1.2%(0.5-2.8) among males and 2.5%(1.5-4.1) among females. The overall chlamydia prevalence was 1.4%(0.8-2.5), with 1.2%(0.5- 2.8) and 1.7%(0.9-3.1) among males and females respectively. Sexually active 18-26-year-old females had highest composite STIs and chlamydia prevalence at 8.7%(3.2-21.4) and 5.8%(1.7-18.2), followed by sexually active young males at 4.8%(1.2-17.6) for both STIs and chlamydia prevalence. Sexually active 40-49-year-old women had the third highest STIs and chlamydia prevalence of 4.5%(2.1-9.2) and 4.1%(1.8-9.0), resulting in a U-shape prevalence distribution among females. Three independent risk factors were identified for both composite STIs and chlamydia, namely younger age, living alone, and males (females with male partners) travelled outside Hong Kong in past 12 months. Compared with those aged 27-39, 18-26-years-old had 6-9 times higher chance of having an STI with AOR=5.81(1.39-24.4); 7.08(1.72-29.1) and 9.48(2.33-38.6) among all, sexually experienced and active participants respectively. Younger participants were more likely to be infected with chlamydia with AOR=6.82(1.36-34.2); 8.04(1.67-38.6) and 9.96(2.09-47.5) among the three categories. Compared with participants living with more than two people, those living alone had higher chances of having an STI including chlamydia with AOR estimated as 12.1(2.07-70.2) and 12.1(1.85-79.1) for composite STIs and chlamydia among the three categories. Compared with males or females whose male partners not travel outside Hong Kong in last year, male travellers (or travellers’ female partners) had higher chance of contracting an STI with AOR=8.21(2.38-28.3); 6.37(1.99-20.4) and 7.01(1.73-28.4) and higher chance of chlamydia infection with AOR=11.1(2.65-46.6); 8.4(2.10-33.5) and 5.35(1.25-22.8) among the three categories. Overall chlamydia prevalence in Hong Kong is similar to that of other countries and regions. Sexually active young people and older women in Hong Kong have relatively high composite STIs and chlamydia prevalence. Mandatory STIs reporting should be considered. Increasing chlamydia screening could be piloted, incorporating key components including cost-effectiveness analysis, result notification and partner notification. Further research on feasibility of scaling up testing is needed.