Statistical Analysis
syphilis, MSM
ADVERSE EVENTS, MINOR, SYPHILIS, SECONDARY, REGRESSION, APPENDIX
A detailed sample size calculation is provided in the Appendix (p. 15). Overall, we calculated 300 indexes required to assess our primary outcome. We report descriptive statistics for sociodemographic and behavioral characteristics in each study arm. All inferential tests were two-sided with a type 1 error level of 0.05. For the primary outcome, we put the number of alters, per index, who provided a verified syphilis test as dependent variable, and intervention arm as independent variable using a negative binomial regression model. Relative risks (RR) and corresponding 95% confidence intervals (CIs) were estimated for the number of alters returning a result per index between each arm. We also conducted a subgroup analysis stratified by age, number of male partners in the past three months, number of MSM that indexes have known in their lives, and self-testing experience of syphilis.The secondary outcomes compared the differences in the proportion of first-time syphilis tested alters, alters with syphilis-reactive results, and reported adverse events among alters. We applied logistic regression modelling to estimate the odds ratio (OR) and corresponding 95% CIs for proportion differences between arms. We also compared the differences on characteristics of indexes who completed follow-up survey or not. All analyses were conducted using SAS version 9.4 (SAS Institute, Cary, NC).We estimated the economic cost of syphilis testing in the three study arms. Costs were categorized as fixed or variable costs. Fixed cost referred to items that were independent of the number of tests conducted, including cost of start-up, building rent and office equipment. Variable cost referred to items that were dependent on the number of tests conducted, including SST kits, standard-of-care testing supplies, and personnel time. Costs related to personnel were calculated by multiplying the staff time associated with each program activity by their hourly wage. We also calculated the cost per alter tested and the cost per alter diagnosed with syphilis. We calculated and ranked the incremental cost-effectiveness ratios (ICERs) to identify the most cost-effective intervention.We followed the intention-to-treat principle and did not have missing data in terms of primary and secondary outcomes. A data monitoring committee was not used as the trial risks were deemed minor. This study was registered in the Chinese Clinical Trial Registry (ChiCTR2000036988). These study findings were reported according to the extension of the CONSORT 2010 statement.