Pay-it-forward Gonorrhea and Chlamydia Testing Among Men Who Have Sex With Men in China: a Cluster Randomized Controlled Trial
Phase: NA
Conditions: Gonorrhea Male, Chlamydia;M
Sponsor: University of North Carolina, Chapel Hill

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Pay-it-forward gonorrhea and chlamydia testing among men who have sex 
with men in China: a study protocol for a three-arm cluster randomized 
controlled trial 
NCT Number: 03741725 
Document date: Aug 16, 2019 
Note: This protocol has been published on Infectious Diseases of Poverty (doi: 10.1186/s40249-
019-0581-1) 
 
 

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Abstract 
Background: Gonorrhea and chlamydia testing is poor among Chinese men who have sex with 
men (MSM). A quasi-experimental study suggested that a pay-it-forward strategy increased dual 
gonorrhea/chlamydia testing among MSM. Pay-it-forward offers an individual a gift (e.g., a free 
test) and then asks the same person if they would like to give a gift to another person. This article 
reports the protocol of a randomized controlled trial to evaluate dual gonorrhea/chlamydia test 
uptake and other outcomes among MSM in three arms – a pay-it-forward arm, a pay-what-you-
want arm, and a standard of care arm. 
Methods: Three hundred MSM will be recruited at three HIV testing sites in Guangzhou and 
Beijing. Testing sites include two hospital-based MSM sexually transmitted diseases clinics and 
one MSM community-based organization. Eligible participants will be born biologically male, 
aged 16 years or older, reporting previous anal sex with another man, having never participated 
in the pay-it-forward program, without previous gonorrhea and chlamydia testing in the past 12 
months, and residing in China. Following a cluster randomized design, every cluster of ten 
participants will be randomly allocated into one of three arms: (1) a pay-it-forward arm in which 
men are offered free gonorrhea and chlamydia testing and then asked whether they would like to 
donate (“pay it forward”) toward testing for future testers; (2) a pay-what-you-want arm in which 
men are offered free testing and told to decide how much to pay after receiving the test; (3) a 
standard of care arm in which men can pay the full price for dual gonorrhoea and chlamydia 
testing. The primary outcome is dual gonorrhoea/chlamydia testing as verified by administrative 
records. Secondary outcomes include incremental cost per test, incremental cost per diagnosis, 
community connectedness, and social cohesion. Primary outcome will be calculated for each arm 

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using intention-to-treat and compared using one-sided 95% confidence intervals with a margin of 
20% increase defined as superiority. 
Discussion: This study will examine the pay-it-forward strategy in comparison to the standard of 
care in improving test uptake for gonorrhea and chlamydia. We will leverage the cluster 
randomized controlled trial to provide scientific evidence on the potential effect and superiority 
of pay-it-forward. Findings from this study will shed light on novel intervention methods for 
increasing preventive health service utilization and innovate ways to finance it among 
communities.  
Trial Registration: ClinicalTrials.gov, NCT03741725. Registered on 12 November 2018. 
Keywords: Men who have sex with men, Gonorrhoea and chlamydia testing, Pay-it-forward, 
Integrated HIV testing, China, Randomized Controlled Trial 
 
 
 

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Background 
Gonorrhea and chlamydia are among the most prevalent sexually transmitted infections (STIs) in 
China.(1, 2) Men who have sex with men (MSM) is a recognized high risk group for STIs and is 
estimated to have a population of 2‒10 million in China.(1, 3) One study conducted from 2015 to 
2017 among MSM in Guangzhou reported an overall gonorrhea prevalence of 12.5% and a 
chlamydia prevalence of 18.1%.(2) Gonorrhea and chlamydia infections are also associated with 
increased risk for HIV transmission and acquisition.(4, 5) Yet, infections are commonly 
asymptomatic and easily missed without screening, especially those at extragenital sites.(6-8) 
For MSM, the World Health Organization recommends periodic testing for asymptomatic 
urethral and rectal gonorrhea and chlamydia using nucleic acid amplification tests (NAAT).(9) 
US Centers for Disease Control and Prevention (CDC) also suggests annual NAAT testing for 
gonorrhea and chlamydia in asymptomatic MSM who are at high risk.(10) 
Yet, gonorrhea and chlamydia testing rate remains low among MSM in China,(11) where studies 
show that less than 50% of MSM have ever been tested.(12, 13) Factors that contribute to poor 
gonorrhea and chlamydia testing among Chinese MSM include poor government funding for 
testing programs,(14) inadequate linking of STI testing to existing HIV testing systems,(15, 16) 
and insufficient MSM community involvement in STI efforts other than HIV. First, few 
government incentives exist to support the additional training and laboratory technology 
associated with regular gonorrhea and chlamydia testing.(14) Second, while many HIV testing 
programs for key populations have began to offer syphilis testing, most are still not set up to 
facilitate comprehensive STI testing.(15, 16) Third, MSM community organizations have had an 
increasing yet still limited role in China’s HIV/STI response(17-19). Most community-based 
outreach programs prioritize HIV, with few focused on gonorrhea or chlamydia(20). 

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In light of this need, several community organizations collaborated with public health staff to 
organize a gonorrhea and chlamydia testing pilot program using a pay-it-forward strategy.(21) In 
pay-it-forward, one person is offered a gift (e.g., a free test), then they are asked whether they 
would like to give a gift to another person.(22, 23) Pay-it-forward has been studied in behavioral 
economics as a form of consumer elective pricing, defined as an economic transaction that 
allows individuals to purchase goods or services for any price (including zero).(24) Pay-it-
forward chains of giving is a type of cooperative behavior that can take place between known or 
anonymous individuals.(25) In social science experiments, pay-it-forward has been shown to 
promote generosity and engage group cohesiveness.(22, 24)  
One pilot study found that pay-it-forward increased gonorrhea/chlamydia testing 19-fold, with 
gonorrhea/chlamydia testing received by 53.7% (109/203) in the pay-it-forward group and 5.9% 
(12/205) in the standard of care group.(21) However, this was not a randomized controlled trial 
(RCT) and the study only compared two groups of individuals. We will evaluate the pay-it-
forward model using a three-arm cluster randomized controlled trial. The purpose of this trial is 
to evaluate a pay-it-forward intervention for increasing gonorrhea and chlamydia testing among 
Chinese MSM.  
 
Methods/design 
Specific aims 
1) Aim 1: To compare the effectiveness of a pay-it-forward program to standard of care in 
promoting gonorrhea/chlamydia testing among Chinese MSM. Hypothesis: Pay-it-
forward is superior to the standard of care in promoting gonorrhea/chlamydia testing. 

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2) Aim 2: To compare the effectiveness of a pay-what-you-want program to standard of care 
in promoting gonorrhea/chlamydia testing among Chinese MSM. Hypothesis: Pay-what-
you-want is superior to the standard of care in promoting gonorrhea/chlamydia testing. 
3) Aim 3: To determine the gonorrhea/chlamydia cost per test and the cost per case 
diagnosed within the three trial arms. Hypothesis: Pay-it-forward is associated with lower 
cost per test and lower cost per case diagnosed. 
 
Methods 
Trial design and timeline 
This study will be a three-arm cluster randomized controlled superiority trial, with the main 
comparisons being pay-it-forward vs standard of care and pay-what-you-want vs standard of 
care. Men will be randomly assigned in a 1:1:1 ratio into three arms. The three arms of the study 
will include: (1) a pay-it-forward arm in which men are offered free gonorrhea and chlamydia 
testing and then given the option to donate (“pay it forward”) toward testing for future testers; (2) 
a pay-what-you-want arm in which men are offered free testing and told to decide how much to 
pay after receiving the test; and (3) a standard of care arm in which men can pay the full price for 
dual gonorrhoea and chlamydia testing (150 RMB, or 22 USD). Men will be recruited at three 
sites: two hospital-based MSM STD clinics in Guangzhou and one MSM community-based 
organization in Beijing.  
Following a cluster randomized design, every cluster of ten participants in each of the three study 
sites will be randomly allocated into one of the three arms independently: pay-it-forward arm, 
pay-what-you-want arm, or the standard of care arm. The rationale for choosing ten participants 
per cluster as the unit of randomization rather than individual participants is to minimize 

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contamination of intervention across individuals and to facilitate cooperation with clinic staff. 
Gonorrhoea/chlamydia testing is performed immediately following each trial arm. 
Gonorrhoea/chlamydia test uptake will be ascertained by assessing administrative records. 
Eligible men will also complete a single survey (see Additional File 1). No follow-up surveys 
will be conducted in this study.  
This study will span approximately three months. The first month will consist of RCT 
preparations and a pilot for the RCT. The following period will consist of RCT recruitment and 
implementation. Recruitment will continue at all sites following a cluster randomization process 
until the pre-determined sample size is reached - a process that is expected to take approximately 
1.5 months. The study will be managed by the Social Entrepreneurship to Spur Health (SESH) 
group, a multi-sectoral implementation research collaboration led by the Southern Medical 
University Dermatology Hospital and the University of North Carolina Project-China.  
 
Study setting and recruitment 
Guangzhou and Beijing are large metropolitan areas with high burdens of STDs and HIV among 
MSM. The RCT will enroll from an STD clinic and a local MSM community-based organization 
(CBO) sites that provide free HIV testing for MSM. The STD clinic site operates within an 
ongoing hospital-based program; the CBO testing site operates within an ongoing community-
based program. All sites already provide free HIV testing to MSM, and are staffed by MSM 
volunteers, nurses, and public health staff. There are no clinical doctors at either site. The staff at 
each site is responsible for handling blood draws, testing, results reporting, and follow-up of HIV 
tests. All sites will follow the same study procedures. 

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Eligibility criteria 
Potential participants must first agree to a print informed consent in order to participate. 
Inclusion criteria are: born biologically male, age 16 years or older, report previous anal sex with 
another man, never participated in the pay-it-forward program, and report one of the following 
with regards to gonorrhoea/chlamydia testing history: not tested for both gonorrhoea and 
chlamydia in the past 12 months, report testing for both gonorrhoea and chlamydia in the past 12 
months with high-risk sexual behaviour following testing, report previous testing for either or 
both gonorrhoea and chlamydia but does not recall whether tested within the past 12 months. All 
eligible participants must provide a working unique mobile phone number or WeChat account 
identification to be enrolled. These will be used only for results notification. 
 
Interventions 
Pay-it-forward arm: The pay-it-forward (PIF) program is developed using crowdsourcing. An 
open challenge contest (26) developed the name and format of the program materials. Hand-
written postcards from previous participants in the program will encourage testing among future 
participants. Community volunteers will provide inputs to the program. At all program sites, 
MSM will be offered dual gonorrhea/chlamydia testing during their appointments for HIV 
testing (Figure 1). First, all men will be provided a brief (five minute) introduction to gonorrhea 
and chlamydia testing using a pamphlet (see Additional file 2). Program organizers will then 
explain the pay-it-forward program to each man using a pamphlet (see Additional file 3). Briefly, 
men will be told that the hospital list price of gonorrhea and chlamydia testing is 150 RMB (22 

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USD), and that previous men attending the clinic had donated money to cover the cost of this 
test. Thus, each man could receive gonorrhea and chlamydia testing for free, then decide whether 
to donate money (pay-it-forward) for future men to have the same option. Men will be assured 
that donating is voluntary and told to pay any amount as they desire. A combination of initial 
research funding and donations from previous participants will be used to cover each man’s 
gonorrhea and chlamydia testing fees. Men will also be shown a postcard with a message written 
in simplified Chinese characters by a previous pay-it-forward contributor and told that they could 
also write a postcard message for a future participant. Men will then decide whether or not to 
receive combined gonorrhea and chlamydia testing. Regardless of their decision to test, men will 
be asked to fill out a brief survey about their sexual history, testing history, attitudes toward the 
testing program, and psychosocial conditions. 
MSM who decide to test will be asked about their sexual practices and will be advised to 
consider receiving urine, anal, or both urine and anal dual gonorrhea/chlamydia testing. All 
participants will be advised that their information will be kept confidential, and that the results 
will be sent to them after approximately one week via WeChat, a phone- and computer-based 
instant messaging application. Men who agree to participate will choose to collect the sample on 
their own or have a staff member assist with sample collection.(27) After sample collection, men 
will decide whether or not to donate money to the next group of participants. Men can choose to 
leave donations for future participants with the program organizers via either cash or WeChat’s 
monetary transfer functionality. Each man will then be invited to write a message on a postcard 
for future pay-it-forward participants.  
Program organizers will inform participants of their test results via WeChat. Samples 
collected in Guangzhou will be stored at room temperature overnight and then transported to 

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Southern Medical University Dermatology Hospital in Guangzhou for laboratory testing 
within one week. Samples collected in Beijing will be shipped in insulated shipping container 
to Southern Medical University Dermatology Hospital for laboratory testing within one 
week. Patients who test positive will be counseled and directed to the WeChat page of the 
designated partnering hospital in each city, where they are able to make an appointment to 
receive treatment and follow-up. 
Pay-what-you-want arm: Pay-what-you-want (PWYW) is a well-documented pricing 
strategy where the buyers decide and pay their desired amount for a given product or service, 
which is usually consumed by themselves.(24) Financially, pay-what-you-want is identical to 
pay-it-forward pricing: the customers choose the price they want to pay for a certain good or 
service, and the seller receives the payments. Socially, pay-what-you-want is different in that 
the customer is paying for him- or herself, while in pay-it-forward the customer is paying on 
behalf of someone else. Just as the pay-it-forward arm, MSM will be offered dual 
gonorrhea/chlamydia testing during their appointments for HIV testing. First, all men will be 
provided a brief (five minute) introduction to gonorrhea and chlamydia testing using a 
pamphlet. Program organizer will then explain the pay-what-you-want program to each man 
separately using verbal descriptions. Briefly, men will be told that the hospital list price of 
gonorrhea and chlamydia testing was 150 RMB (22 USD). Then they will be told that if they 
were to test today, they can participate in the pay-what-you-want program, in which they 
receive the test first and then decide how much they would like to pay. Men will be assured 
that payment is completely optional and advised to pay any amount that is desired by them. 
Men will then decide whether or not to receive urine, anal, or both urine and anal dual 
gonorrhea/chlamydia testing. Each man’s gonorrhea and chlamydia test fees will be covered 

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by a combination of the initial research funding from the program organizers and payments 
from participants.  
All participants will be ensured that their information will be kept confidential. Procedures 
for sample collection, sample processing, payment method, results reporting, and treatment 
linkage will be identical to those of the pay-it-forward arm.   
Standard of care arm: Among men assigned to the standard of care arm, gonorrhea and 
chlamydia testing will be offered at the usual hospital list price (150 RMB, $22 USD). All 
men will be provided a brief introduction about gonorrhea and chlamydia testing using the 
same pamphlet, but will not be introduced to other content of the above arms. Procedures for 
sample collection, sample processing, payment method, results reporting, and treatment 
linkage will be identical to those of the pay-it-forward arm.   
[Insert Figure 1 here] 
Figure 1. Schematic of three trial arms. The block diagrams describe the implementation steps for each 
arm. 
 
Randomization and allocation 
At each site, men will be assigned to one of the three arms through a cluster randomization 
procedure with ten participants per cluster (Figure 2). To ensure equal number of clusters in each 
of the three arms, the clusters will be randomized in a block of three at each study site. The 
schedule will be determined prior to start of the study and then provided to each of the sites. 
STATA 15 software will be used to create the allocation sequence.(28) Ten blocks will be 

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generated in total. Each block has three clusters consisting of pay-it-forward, pay-what-you-
want, and standard of care, randomly created from all possible permutations.  
Each eligible individual who presents to the site during a given 10-person cluster will be 
provided the allocated program. This RCT is not blinded. Participants will be able to determine 
their assignment based on whether they received intervention materials during the study period. 
Study organizers will be aware of randomization assignment because intervention materials 
provided to participants. 
[Insert Figure 2 here]    
Figure 2. Schematic of cluster randomization procedure and sample allocation. This schematic diagram 
illustrates the cluster randomization procedure, average volume of testers who visit the study site for 
HIV tests during a typical week, and allocation. There are 30 clusters and 300 total participants, which 
satisfy the sample size. The sequence shown is for illustration and is not the actual allocation sequence. 
 
Laboratory testing 
All urine and anal samples will be analyzed using Cobas 4800 CT/NG DNA detection kits 
(Roche Diagnostics, Basel, Switzerland) at Southern Medical University Dermatology Hospital. 
At the two MSM STD clinic sites, HIV testing will be performed using the Diagnostic Kit for 
Antibody to HIV ½ (Abon Pharmaceuticals, Northvale, New Jersey, USA) and syphilis testing, 
for those that choose to test, will be performed using the Treponema Pallidum Antibodies Rapid 
Test (Abon Pharmaceuticals, Northvale, New Jersey, USA). At the CBO site, HIV testing will be 
performed using the Third Generation Diagnostic Kit for Antibody to HIV rapid test (InTec, 
Xiamen, China ) and syphilis testing, for those choosing to test, will be performed using the 
Syphilis Antibody (anti-Treponema Pallidum) rapid test (InTec, Xiamen, China).  

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Sample size  
Sample size calculation (Table 1) is informed by a quasi-experimental study conducted in 2017‒
2018 at two similar study sites(21) and by a pilot study for the RCT conducted from October to 
November 2018. In the quasi-experimental study, gonorrhea/chlamydia testing was 53.7% in the 
pay-it-forward group and 5.9% in the standard of care group. In the pilot study for the RCT 
(Table 2), gonorrhea/chlamydia testing was 88% in the pay-it-forward group and 42% in the pay-
what-you-want group. Based on these results and pilot data for the RCT, we assume that in the 
RCT we will have 54% test uptake in the pay-it-forward group, 42% test uptake in the pay-what-
you-want group, and 6% in the standard of care. For the pay-it-forward uptake estimate, we 
chose to use the quasi-experimental study results (54%) instead of the pilot results (88%) 
because the quasi-experimental study was considered more similar in nature to our RCT, given 
that the pilot focused primarily on implementation optimization.  
We will have three arms -- pay-it-forward, pay-what-you-want, standard of care, with numbers 
of clusters at a ratio of 1:1:1. The trial between pay-it-forward and standard of care will be 
testing superiority in promoting gonorrhea/chlamydia test uptake at a superiority margin of 0.2 
(20% difference in percentage agreeing to test in those two arms). This margin was chosen as a 
clinically significant difference in test uptake based on results from a modeling study.(29) 
Similarly, the trial between pay-what-you-want and standard of care will be also testing 
superiority with the same margin of 0.2. Assuming we will have three equal sized arms, with 
cluster size of 10 per cluster, alpha of 0.05, power of 0.8, inter class correlation of 0.01 or 005, 
we will at most need eight or 11 clusters per arm, respectively (Table 1). To integrate the sample 
size calculations and to consider practicality, the final sample size would be ten clusters in pay-

14 
 
it-forward, ten clusters in pay-what-you-want, and ten clusters in standard of care, with a total 
cluster size of 30 (300 participants).  
Table 1. Sample size calculations.  
Pay-it-forward and standard of care 
ICC 
0.01 
0.05 
Proportion in control group 
0.06 
0.06 
Superiority margin 
0.2 
0.2 
Proportion in intervention group assuming H0 
0.26 
0.26 
Proportion in intervention group assuming H1 
0.54 
0.54 
Difference at which power is calculated 
0.48 
0.48 
Number of people per cluster 
10 
10 
Alpha 
0.05 
0.05 
Power 
0.8 
0.8 
Total sample size per arm 
30 
40 
Number of clusters per arm 
3 
4 
Pay-what-you-want and standard of care 
ICC 
0.01 
0.05 
Proportion in control group 
0.06 
0.06 
Superiority margin 
0.2 
0.2 
Proportion in intervention group assuming H0 
0.26 
0.26 
Proportion in intervention group assuming H1 
0.42 
0.42 
Difference at which power is calculated 
0.36 
0.36 
Number of people per cluster 
10 
10 
Alpha 
0.05 
0.05 
Power 
0.8 
0.8 
Total sample size per arm 
80 
110 
Number of clusters per arm 
8 
11 
 
ICC: Intra-class correlation.  
Quality control 
We will examine data collected from all participants. We will deduplicate participants by 
examining cell phone number and WeChat handle. The primary outcome for this study is uptake 
of dual gonorrhea/chlamydia testing by administrative record as a single outcome. For the pay-it-

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forward arm, we will record the amount that each participant donates to future participants. For 
the pay-what-you-want arm, we will record the amount that participants pay for their own test.  
Information on socio-demographics, sexual behaviors, HIV/STI testing history, and psychosocial 
conditions will be collected using a standardized survey instrument. Socio-demographic 
characteristics include participants’ age, ethnicity, marital status, highest level of education 
completed, place of residency (urban or rural), and annual income level. Sexual behaviors and 
HIV/STI testing history include previous anal sex with men, role during anal sex, number of sex 
partners, condom use, sexual orientation disclosure, endorsement of STI symptoms, and testing 
history for HIV, gonorrhea, and chlamydia. Psychosocial variables include adapted measures for 
community engagement,(30) community connectedness,(31) identify fusion,(32) and social 
cohesion.(33, 34) For all participants, we will collect HIV test results, as well as gonorrhea and 
chlamydia results for those who tested. We will also collect information on reasons for accepting 
or declining gonorrhea and chlamydia tests. For men assigned to the pay-it-forward group, we 
will also ask about perceived benefits and barriers of the pay-it-forward program. Upon 
completion of the study survey, participants will receive a pen valued approximately one USD.  
 
Outcomes 
The main outcome of this study will be gonorrhea and chlamydia testing by PCR as assessed by 
administrative records. The choice of diagnostics is based on World Health Organization and US 
CDC guidelines recommending regular gonorrhea/chlamydia testing among MSM with risks.(9, 
10) Secondary outcomes will include incremental cost per test, incremental cost per diagnosis, 
community connectedness, and social cohesion. Effect modification analysis will include 

16 
 
community engagement. Existing literature on community engagement,(30) community 
connectedness,(31, 32) and social cohesion,(33, 34) informed the development of adapted scales 
in this study. Community engagement is measured using an adapted six-item yes/no scale used in 
a previous study on Chinese MSM.(30) A six-item community connectedness scale(31) and a 
seven-item social cohesion scale(33, 34) ask participants to rank their level of disagreement and 
agreement with each item using answer choices “Strongly Agree,” “Agree,” “Disagree” and 
“Strongly Disagree”. All three community scales were adapted to the local context and piloted 
among 43 Chinese MSM before RCT recruitment. Survey items are detailed in Additional file 1.   
 
Confidentiality 
Survey data will be collected partially from online-based questionnaire and then stored on a 
secure online survey platform (Wenjuanxing), and partially from paper-based questionnaire. 
Electronic data will be transmitted using 128-bit encryption across the Internet and mobile data 
networks. Paper-based data will be entered by research staff members on the same day as data 
collection. Responses to surveys, including participant mobile phone numbers and WeChat 
account numbers, will be stored on a secure server (electronic) and in a locked cabinet (offline), 
which can be accessed with login information known only to the research team. 
 
Monitoring 
A data monitoring committee will not be formed for this RCT because potential for harm to 
participants is minimal. If any person feels they have experienced an adverse event or unwanted 
effect from participating in this RCT, they can withdraw at any time. A telephone number and 

17 
 
WeChat account will be provided to participants to contact the primary investigator with 
questions or concerns. 
Data analysis 
Primary analysis 
Socio-demographic characteristics will be summarized using descriptive statistics. The 
gonorrhoea/chlamydia test uptake rate will be calculated for each of the three arms. Generalized 
estimating equations will be used to account for potential correlation in outcomes due to 
clustering. The primary analysis will evaluate the hypotheses that the pay-it-forward intervention 
is superior to standard of care and that the pay-what-you-want intervention is superior to 
standard of care. The trial between pay-it-forward and standard of care will be testing superiority 
in promoting test uptake at a superiority margin of 20% in percentage agreeing to test in those 
two arms(29). The trial between pay-what-you-want and standard of care will be testing with the 
same 20% margin. One-sided 95% confidence interval will be computed for pay-it-forward vs 
standard of care and for pay-what-you-want vs standard of care, and then compared to the 
superiority margin.  
Subgroup analysis 
Effect modification analyses will evaluate whether the effect of the pay-it-forward intervention 
on gonorrhoea/chlamydia test uptake varied in relation to the following factors: (1) younger age 
(less than 28 years old, 28 or older); (2) community-level constructs: community engagement 
(high or low level), community connectedness (high or low level), social cohesion (high or low 
level). For each factor of interest, three measures of association will be calculated: A) a crude 
measure of association between treatment group and test uptake, B1) a measure of association 

18 
 
between treatment group and test uptake among all participants who report the factor of interest 
(younger age, or high level of a community-level construct), B2) a measure of association 
between treatment group and test uptake among all participants who deny a history of having the 
factor of interest (younger age, or high level of a community-level construct). Effect 
modification will be deemed present when B1 and B2 are different from one another, and at least 
one (B1 or B2) is different from A.  
Missing data plan 
Men will only be involved at a single time point and so there is no loss to follow up. However, 
there may be missing data in the primary and secondary outcomes. If the primary outcome is 
missing for <15% of participants, analyses will use a complete-case approach. If an outcome is 
missing for ≥15% of participants, missingness mechanism will be investigated and multiple 
imputation will be used if suitable. 
Secondary analyses 
Within each arm of the study, we will calculate the incremental cost per test and the incremental 
cost per diagnosis. Cost will be collected from the perspective of the program provider. To 
estimate the program cost, we will identify the cost of each program element, such as personnel, 
facilities, equipment, and materials, and categorize costs into start-up costs, fixed costs, and 
variable costs. Start-up costs are incurred in the period between the decision to implement this 
trial and the start of trial recruitment (e.g. personnel training, testing sites coordination, pilot 
study). Fixed costs remain constant during the trial period regardless of the number of people 
served (e.g. administration, durable goods, and equipment). Variable costs are those that vary 
with the number of participants served (e.g. recruitment, counselling and testing, and nondurable 

19 
 
goods and supplies). Personnel costs will be calculated by multiplying the staff time associated 
with each program activity by the compensation received by the staff who perform these 
activities. We will first calculate the total cost for each group, then divide these costs by the 
number of men tested and by the number of cases diagnosed with gonorrhea or chlamydia.   
 
Pilot study results summary 
To inform the development of this randomized controlled trial, the pay-it-forward and pay-what-
you-want arms were evaluated through a pilot study conducted from October 2018 to November 
2018 (Table 2).  
A total of 43 eligible MSM were recruited at the selected study sites for the RCT. Recruitment 
took place on nine days interspersed between 13 October and 15 November All men on a given 
day were assigned to either pay-it-forward or pay-what-you-want arm. In total, 17 men were 
recruited for the pay-it-forward arm over four days; 26 men were recruited for the pay-what-you-
want arm over five days. Of these, 88% (15/17) of men received gonorrhea/chlamydia testing in 
the pay-it-forward arm and 42% (11/26) of men received gonorrhea/chlamydia testing in the pay-
what-you-want arm.  All men (100%, 15/15) in the pay-it-forward arm donated some amount, 
with average donation per participant of 56 RMB. 91% (10/11) of men in the pay-what-you-want 
paid some amount, with average payment per participant of 42 RMB. None were diagnosed with 
gonorrhea and three men were diagnosed with chlamydia.  
These pilot results, along with results of a quasi-experimental study among 408 men,(21) were 
used as the basis to inform sample size calculation. Through this pilot period, implementation 

20 
 
steps and survey instrument were also optimized through an iterative process consisting of 
feedback from MSM participants, organizers, and community partners.  
 
Table 2. Two piloted arms and the historical standard of care.    
 
Arms 
Standard of care* 
Pay-it-forward 
Pay-what-you-want 
Days piloted 
52 
4 
5 
Number of MSM 
offered intervention 
205 
17 
26 
GC/CT test uptake 
12 (6%) 
15 (88%) 
11 (42%) 
Number of MSM who 
contributed any amount 
NA 
15 (100%) 
10 (91%) 
Total contribution 
amount 
NA 
833.88 RMB (125.08 
USD) 
465.99 RMB (69.90 
USD) 
Average contribution 
Amount per tester 
NA 
55.59 RMB (8.34 
USD)  
42.36 RMB (6.35 
USD) 
Gonorrhea positive 
NA 
0 
0 
Chlamydia positive 
NA 
2 
1 
*Historical standard of care data from a quasi-experimental study between March 11th and May 
1st, 2018. 
MSM: Men who have sex with men 
GC/CT: Gonorrhea and chlamydia 
NA: Not applicable. 
 

21 
 
Discussion 
This trial will assess the effectiveness of pay-it-forward intervention in promoting gonorrhoea 
and chlamydia testing among Chinese MSM, a marginalized population where sustainable 
strategies for integrated HIV/STD testing programs are urgently needed. Few studies have 
evaluated the use of pay-it-forward interventions focused on improving health, and none to our 
knowledge have used a RCT design. This three-arm cluster RCT will demonstrate pay-it-
forward’s ability to be effective in the complex context of local settings. The pay-it-forward 
model includes both free or subsidized testing and a sense of social obligation to contribute to the 
health of other gay men. With comparison to the pay-what-you-want arm, a model that is 
financially similar to pay-it-forward but socially contrasting, there is an opportunity to explore 
the extent to which social and financial factors contribute to pay-it-forward health programs.  
Although this trial will yield important insights for STD testing programming in China, some 
limitations exist. The RCT will be conducted at sites of HIV/syphilis testing for MSM. This 
limits our sample to MSM who are undergoing HIV/syphilis testing and are connected with 
community-based organizations. The level of trust that MSM hold toward sites in which pay-it-
forward programs are embedded may influence program effectiveness. The testing sites in this 
study are long-standing programs and trusted by the MSM community. Findings may be limited 
in generalizability to settings that lack existing HIV testing services or trusted sites for MSM.  
Our study will generate important research and policy implications regarding the use of pay-it-
forward to preventative health services. The study outcomes will help guide policy and 
intervention practice of governmental departments and community-based organizations 
regarding the expansion of key population STD testing strategies. Moreover, practical 

22 
 
knowledge gained from developing and implementing an innovative, pay-it-forward intervention 
may be applicable for future efforts to build self-sustaining STD testing programs.   
Trial status  
At the time of writing this article, RCT recruitment is ongoing. Data analysis for the RCT has not 
begun. The study is registered in the Clinical Trials.gov database (NCT03741725). The database 
will also be used for documenting protocol modifications. The trial protocol conforms to the 
Standard Protocol Items: Recommendation for Interventional Trials (SPIRIT) 2013 statement.  
 
List of abbreviations 
CBO  
Community-based organization 
CDC  
US Center for Disease Control and Prevention 
H0 
 
Null hypothesis 
H1 
 
Alternative hypothesis 
LMIC  
Low- and middle-income countries 
MSM  
Men who have sex with men 
RCT 
 
Randomized controlled trial 
SESH  
Social Entrepreneurship to Spur Health Group 
 
Declarations 
Ethics approval and consent to participate  

23 
 
Institutional Review Board (IRB) approval has been obtained from the following institutional 
ethical review boards prior to study enrollment: Southern Medical University Guangdong 
Provincial Center for Skin Diseases and STI Control (China), Yale University (USA), and 
University of North Carolina at Chapel Hill (USA). All participants will provide consent prior to 
taking part in the study (see Additional file 4).  
Consent for publication  
Not applicable. 
Availability of data and material 
Not applicable. 
Competing interests 
The authors declare that they have no competing interests. 
 
Funding 
This study received support from the National Key Research and Development Program of 
China (2017YFE0103800), the National Institutes of Health (NIAID 1R01AI114310-01; 
1UG3HD096929-01), UNC-South China STD Research Training Center (FIC 1D43TW009532-
01), UNC Center for AIDS Research (NIAID 5P30AI050410), Doris Duke Charitable 
Foundation (International Clinical Research Fellowship to TZ), and SESH (Social 
Entrepreneurship to Spur Health) Global. The funders had no role in study design, data 
collection, and analysis, decision to publish, or preparation of the manuscript. The authors thank 
all people who contributed to this study. 
Author’s contributions 
JT, MA, LF, KL, TZ, FY, and WT conceived the study. TZ and FY led pilot and implementation 
optimization. TZ, FY, MA, LF, and NK participated in survey development. FY, FZ, and WT 

24 
 
provided statistical expertise. LY, GM, YW, WH, AL, WZ, and DW assisted with recruitment. 
PV advised modeling approaches. FY, YW, AL, WZ, LY, and WT are leading implementation in 
Guangzhou. TZ, WH, and GM are leading implementation in Beijing. JT, NC, BY, and WT 
provided oversight. JT, MA, and LF wrote initial drafts of the paper. TZ redrafted and finalized 
the paper with inputs from FY, WT, NK, DW, and JT. All authors read and authorized the final 
version.  
Acknowledgements 
We thank all study participants, CBO volunteers, and staff members at Social Entrepreneurship 
to Spur Health (SESH) Global, Zhitong Guangzhou LGBT Center, BlueD, and Southern Medical 
University Guangdong Provincial Center for Skin Diseases and STI Control who contributed.  
 
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Additional files 
Additional file 1 
Format: docx. 
Title: Survey instrument (English version) 
Description: This is the English version of the survey for our study.  
 
Additional file 2 
Format: pptx. 
Title: Introduction to Gonorrhea and Chlamydia pamphlet (English version) 
Description: This is the English version of the pamphlet used by study organizers to introduce 
Gonorrhea and Chlamydia to eligible men. 
 
Additional file 3 
Format: pptx. 

27 
 
Title: Introduction to Pay-It-Forward pamphlet (English version) 
Description: This is the English version of the pamphlet used by study organizers to introduce 
pay-it-forward to eligible men. 
 
Additional file 4 
Format: docx. 
Title: Informed consent form (English version) 
Description: This is the English version of the informed consent form for our study.