The disproportionate burden of HIV and STIs among male sex workers in Mexico City and the rationale for economic incentives to reduce risks

Abstract

Introduction
The objective of this article is to present the rationale and baseline results for a randomized controlled pilot trial using economic incentives to reduce HIV and sexually transmitted infection (STI) risk among male sex workers (MSWs) in Mexico City.

Methods
Participants (n=267) were tested and treated for STIs (chlamydia, gonorrhoea, syphilis and HIV) and viral hepatitis (hepatitis B and C), received HIV and STI prevention education and were randomized into four groups: (1) control, (2) medium conditional incentive ($50/six months), (3) high conditional incentive ($75/six months) and (4) unconditional incentive ($50/six months). In the conditional arms, incentives were contingent upon testing free of new curable STIs (chlamydia, gonorrhoea and syphilis) at follow-up assessments.

Results
Participants’ mean age was 25 years; 8% were homeless or lived in a shelter, 16% were unemployed and 21% lived in Mexico City less than 5 years. At baseline, 38% were living with HIV, and 32% tested positive for viral hepatitis or at least one STI (other than HIV). Participants had a mean of five male clients in the previous week; 18% reported condomless sex with their last client. For 37%, sex work was their main occupation and was conducted mainly on the streets (51%) or in bars/discotheques (24%) and hotels (24%). The average price for a sex transaction was $25 with a 35% higher payment for condomless sex.

Conclusions
The findings suggest that economic incentives are a relevant approach for HIV prevention among MSWs, given the market-based inducements for unprotected sex. This type of targeted intervention seems to be justified and should continue to be explored in the context of combination prevention efforts.

Full text

Research article
The disproportionate burden of HIV and STIs among male sex
workers in Mexico City and the rationale for economic incentives
to reduce risks
Omar Gala
´rraga
§,1,2
, Sandra G Sosa-Rubı
´
2
, Andrea Gonza
´lez
3
, Florentino Badial-Herna
´ndez
3
, Carlos J Conde-Glez
2
,
Luis Jua
´rez-Figueroa
3
, Sergio Bautista-Arredondo
2
, Caroline Kuo
1,4
, Don Operario
1
and Kenneth H Mayer
1,5,6
§
Corresponding author: Omar Gala
´rraga, Department of Health Services Policy and Practice, Brown University School of Public Health, 121 South Main Street,
Box G-121S-7, Providence, RI 02912, USA. (omar_galarraga@brown.edu)
Abstract
Introduction: The objective of this article is to present the rationale and baseline results for a randomized controlled pilot trial
using economic incentives to reduce HIV and sexually transmitted infection (STI) risk among male sex workers (MSWs) in Mexico
City.
Methods: Participants (n267) were tested and treated for STIs (chlamydia, gonorrhoea, syphilis and HIV) and viral hepatitis
(hepatitis B and C), received HIV and STI prevention education and were randomized into four groups: (1) control, (2) medium
conditional incentive ($50/six months), (3) high conditional incentive ($75/six months) and (4) unconditional incentive ($50/six
months). In the conditional arms, incentives were contingent upon testing free of new curable STIs (chlamydia, gonorrhoea and
syphilis) at follow-up assessments.
Results: Participants’ mean age was 25 years; 8% were homeless or lived in a shelter, 16% were unemployed and 21% lived in
Mexico City less than 5 years. At baseline, 38% were living with HIV, and 32% tested positive for viral hepatitis or at least one STI
(other than HIV). Participants had a mean of five male clients in the previous week; 18% reported condomless sex with their last
client. For 37%, sex work was their main occupation and was conducted mainly on the streets (51%) or in bars/discotheques
(24%) and hotels (24%). The average price for a sex transaction was $25 with a 35% higher payment for condomless sex.
Conclusions: The findings suggest that economic incentives are a relevant approach for HIV prevention among MSWs, given the
market-based inducements for unprotected sex. This type of targeted intervention seems to be justified and should continue to
be explored in the context of combination prevention efforts.
Keywords: male sex workers; men who have sex with men; conditional cash transfer; conditional economic incentives;
HIV/STI prevention; risk premium; compensating differential; Mexico.
Received 31 March 2014; Revised 1 October 2014; Accepted 16 October 2014; Published 14 November 2014
Copyright: –2014 Gala
´rraga O et al; licensee International AIDS Society. This is an Open Access article distributed under the terms of the Creative Commons
Attribution 3.0 Unported (CC BY 3.0) License (http://creativecommons.org/licenses/by/3.0/), which permits unrestricted use, distribution, and reproduction in any
medium, provided the original work is properly cited.
Introduction
Mexico, a country of 112 million people, has a concentrated
HIV epidemic [1] with an HIV prevalence of 0.3% in the adult
population (1549 years), 16.9% among men who have sex
with men (MSM), and 18.2% among male sex workers
(MSWs) [2,3]. The elevated HIV risk among MSM has been
associated with behavioural factors including multiple sexual
partners and inconsistent condom use [412]. Other factors,
such as poverty and economic insecurity, also determine
behavioural risks; and, as such, interventions that alleviate
the socioeconomic pressures that underpin behavioural risk
taking can reduce HIV and other sexually transmitted
infections (STIs) among MSWs [1319].
Conditional cash transfer (CCT) interventions are a type
of economic intervention that incents specific behaviours
linked to positive outcomes such as improved health [20].
CCT interventions have been implemented in generalized HIV
epidemic settings (Tanzania and Malawi) and have proved
effective in reducing HIV and STI risks and prevalence [21,22].
Similarly, CCTs have been used in Mexico since the late 1990s
through programmes that provide incentives to poor families
to keep school-aged children in school and attend preventive
health check-up visits [23]. No efforts in Mexico, how-
ever, have directly linked incentives for HIV and STI preven-
tion, including regular STI medical check-ups and treatment,
targeting populations at high risk. This novel approach shows
promise in light of Mexico’s history of economic interventions
to promote public health, and its concentrated HIV epidemic
disproportionately affecting MSM. This article describes an
effort to adapt a CCT intervention to the context of HIV
and STI prevention services for economically disadvantaged
MSWs in Mexico City.
Interventions to incent safer sexual behaviours can counter-
act the market-based inducements that sex workers receive
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´rraga O et al. Journal of the International AIDS Society 2014, 17:19218
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1

from clients to engage in increased risk (i.e., condomless sex).
This risk premium (as it is called in economics) has been
documented among female sex workers in India, Mexico
and Bangladesh [2426] and among MSWs in Ecuador [27].
Avoiding clients who pay higher prices for unprotected sex
implies monetary losses for MSWs. Thus, compensation in the
form of economic incentives for self-protection can offer one
method for reducing risk behaviours and improving individual
and population health.
This article describes the developmental process and
rationale for a CCT intervention for HIV and STI prevention.
The Punto Seguro (‘‘Secure Point’’) intervention involves a
randomized controlled design to pilot test whether CCT
can reduce HIV risks among MSWs. To our knowledge, this
is the first systematic adaptation of CCT of this nature. The
rationale for working with MSWs is that they are a vulnerable
population with high rates of STI and HIV infection or at
high risk of contracting these diseases. Furthermore, male-
male transactional sex has been identified as an important
driver of the concentrated epidemic in Mexico. Currently,
no effective HIV prevention or social programmes exist for
this key population in Mexico City. Another innovative aspect
is that the levels of the incentives tested were estimated
via willingness-to-accept methods [28]. Thus, the aims of
this article are to (1) describe the sociodemographic
characteristics of the Punto Seguro cohort, (2) present the
baseline HIV and STI risk and prevalence rates and (3) analyse
commercial sex transaction prices, exploring if a risk premium
exists for MSWs in Mexico City which might further drive
unprotected sex with paying male clients.
Methods
Setting
This research was conducted in Mexico City at Clı
´nica
Condesa, which started providing HIV specialized care in
2000. The primary purpose of Clı
´nica Condesa is to provide
medical assistance to the Mexico City population who is living
with HIV and of low socioeconomic status; prevention is also
an important part of its mission. An initiative to expand
HIV testing and counselling services for key populations at
high risk of infection has been implemented since 2009.
Free treatment for HIV and other STIs is included as a service
for the target population.
Participants: inclusion and exclusion criteria
The inclusion criteria were as follows: men; 1840 years of age;
and self-identified as MSWs, or as MSM who had penetrative
or receptive anal sex with another man in exchange for money
in the last six months and who had 10 or more male sexual
partners in the last month. The exclusion criteria were un-
willingness to sign an informed consent form to participate
in the study, inability to read or speak Spanish and/or inability
to respond to the screening questionnaire because of the
influence of drugs or alcohol. Transgender individuals were
excluded from this study because Clı
´nica Condesa has a
separate programme for them. Participants were recruited
by trained research staff through direct outreach to commu-
nity sites where MSW congregate, identified from previous
studies [17,28]. Participants also were recruited from within
the Clı
´nica Condesa HIV Testing Clinic, for example after using
voluntary counselling and testing services and being referred
to the research team. We had strict procedures with separated
roles (for clinical and research categories) ensuring an under-
standing that regular clinic services would not be denied
regardless of a participant’s decision to enrol in the study.
We used several strategies for ensuring recruitment from
a diverse sample: the recruitment team (a) regularly visited
the sites where sex workers congregate, mainly La Alameda,
and a visit was made at least once a week during the busiest
times so that participants could be invited; (b) provided
transportation to participants so that they could more
easily obtain check-ups and STI test results from the clinic;
(c) involved qualified personnel (a health counsellor and
psychologist) with several years of experience working with
the community; and (d) set up a referral process to recruit
eligible individuals who were already attending Clı
´nica
Condesa.
Data collection
Data collection took place in collaboration with the Mexican
National Institute of Public Health (INSP) and Consortium
for HIV/AIDS and TB Research (CISIDAT). All participants were
interviewed at Clı
´nica Condesa. Interviews took place in a
private area using portable laptop computers with audio
computer-assisted interviewing (A-CASI) questionnaires. Elec-
tronic records were de-identified, and only code numbers
were used for data analysis. Identifiable private information
was available only to clinical staff (and used solely for follow-
up and treatment referral purposes).
The primary outcomes were self-reported condom use
(with last three clients; as well as intentions for condom use
[29]) and self-reported number of sexual partners (commer-
cial and non-commercial). The secondary outcomes were
self-reported STIs and commercial sex transaction prices (for
protected and unprotected sex episodes, by type of sexual
act). Biological outcomes were as follows: testing in all
groups was conducted for chlamydia, gonorrhoea, syphilis,
hepatitis B, hepatitis C and HIV.
Participants provided blood and urine samples for testing.
Specimens were collected under standard bio-safety pro-
tocols by trained staff and analysed by lab technicians. Urine
specimens were collected and tested for gonorrhoea and
chlamydia (PCR Cobas-Amplicor; Roche, Basel, Switzerland),
and blood specimens served to measure the presence of HIV,
hepatitis B, hepatitis C and syphilis antibodies (Abbott HIV-1
and HIV-2, Ag/Ab Combo, anti-HBc, anti-HCV and syphilis
TP quimioluminiscence immunoassay (Abbott Laboratories,
North Chicago, IL, USA) running in Architect i2000 (Abbott);
HIV-positive samples were confirmed with HIV-1 and HIV-2
CombFirm (Orgenics, Yavne, Israel); and anti-HBcwas tested
with Determine HBsAg and syphilis TP(Abbott) with tittered
VDRL (the Venereal Disease Research Laboratory test)). At the
baseline survey, two subgroups were defined for the markers
of syphilis and hepatitis B: antibody positivity was regarded
as a lifetime marker of past or present infection, whereas
treponemic antibody positivity together with VDRL demon-
strated active syphilis, and anti-HBc plus HBsAg positivity
indicated current hepatitis B virus infection. All participants
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´rraga O et al. Journal of the International AIDS Society 2014, 17:19218
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2

received results from trained male health care providers
certified in STI and HIV counselling, and any participant with
positive results for any STI was referred for treatment (free
of charge) at Clı
´nica Condesa following the standard guidelines
for counselling, testing and treatment of HIV and STIs in
Mexico. Participants living with HIV and/or viral hepatitis were
still eligible to stay free of new curable STIs (chlamydia,
gonorrhoea and syphilis), and they could still receive the
incentives if they had been randomized to an incentive arm.
All participants provided informed consent, and all procedures
were approved by Institutional Review Board (IRB) commit-
tees at the Mexican National Institute of Public Health (INSP)
and at Brown University.
CCT adaptation
This intervention is part of a randomized controlled pilot,
Punto Seguro. The pilot trial has four arms: control group,
medium conditional incentives (600 pesos, or about $50,
every six months), high conditional incentives (900 pesos, or
about $75, every six months), and unconditional incentives
(600 pesos every six months). Participants in the conditional
arms receive the incentive amount if they tested negative for
new curable STIs (chlamydia, gonorrhoea and syphilis) at
months 6 and 12. In the unconditional arm, they receive
the medium incentive regardless of new curable STI status.
The amounts of the incentives were established using an
economic approach for willingness-to-accept (WTA) [28].
We used a computer experiment to measure the optimal level
of incentives by interviewing 1,745 MSM and MSWs, and
we found that at a rate of $288 a year, more than three-
quarters of the men would attend prevention talks, engage in
testing for STIs and attempt to stay free of STIs. To obtain
a similar level of participation among the subsample who
were MSWs, the price was lower: $156 a year. Thus, potential
participants felt that these amounts were relevant, based
on previous research. Also, to limit any potentially negative
framing effects, we avoided the term ‘‘low incentive’’ and
always referred to medium and high incentives. Moreover, we
also purposely tried to keep the incentive levels as low as
possible with the issues of sustainability and potential cost-
effectiveness in mind. Given the high costs of HIV treatment in
Mexico [30] of about $5,000 to $7,000 per person per year, if
the intervention helps individuals avoid HIV infections, then
there may be cost savings in the long run. Because cash may
have unintended consequences, such as increased use of
alcohol and drugs, we used vouchers for food and groceries as
a form of payment when the conditionality was fulfilled,
as well as for the inconvenience fees and the uncondi-
tional incentive payments. Hence, we called the intervention
‘‘conditional economic incentives’’ (CEIs) instead of CCT.
Statistical procedures and analysis
We first present descriptive statistics for sociodemographic
data (Table 1) as well as STI and HIV risks (Table 2), showing
the sample sizes responding to each specific question. Next,
we present cross-tabulation tables of self-report versus
actual STI/HIV status (Table 3). We also report commercial
sex transactions during the past week in terms of the highest
price, the lowest price and the average price, as well as for
the last three clients (Table 4). Given the participants’
estimations of highest, lowest and average prices in the
past week, we report the mean, standard deviation, median,
minimum and maximum. We placed more emphasis on the
median results because of the presence of large outliers.
Finally, we analysed the differences between prices for
commercial sex with and without a condom (Table 5). In
economics, this difference is called a compensating dif-
ferential or risk premium because sex workers are paid
higher prices when they have more risk [27,31], a phenom-
enon observed in other occupations as well [32]. We follow
methods used in the female commercial sex markets in
Mexico, Ecuador and India [24,25,31] and among MSWs in
Table 1. Baseline sociodemographic characteristics
Sociodemographic variables Nn% Mean (SD)
Age (years) 253 24.7 (4.68)
Schooling 250
16 years 31 12.4
79 years 73 37.6
1012 years 94 20.8
13 or more years 52 37.3
Marital status 252
Married/free union 50 19.8
Single 199 78.9
Separated/widower 3 1.19
Main occupation now 242
Work (non-sexual) 54 22.3
Unemployed 39 16.1
Student 36 14.8
Sex work 90 37.1
Own business 12 4.96
Other 11 4.55
Housing 245
Own an apartment or home 65 26.3
Rent an apartment or home 99 40.4
Staying at friend’s house or apartment 25 10.2
Rent room (hotel, motel, pension) 35 14.2
On the street 13 5.31
Other 8 3.26
Has been in Mexico City less than 5 years 211 45 21.3
Does not have health insurance 238 124 52.1
Sex work location 186
Bar/disco/pub 45 24.1
Hotel/motel 45 24.1
Street/public park 94 50.5
Sex club 6 3.23
Beauty salon 5 2.69
Massage parlour 9 4.84
Sauna/bath house 13 6.99
Other 11 5.80
Table presents percentages, unless otherwise noted.
Ntotal respondents; nresponses for specific question; SD
standard deviation.
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´rraga O et al. Journal of the International AIDS Society 2014, 17:19218
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Ecuador [27]. We estimated a log-linear equation using the
log of the commercial sex transaction price as the dependent
variable, and a dummy variable (1 if no condoms were
used) as the main explanatory variable. The log transformation
helped to linearize the distribution and enabled us to apply
linear regression methods.
Results
Table 1 shows the baseline sociodemographic characteristics
of the participants. The mean age was 25 years; 12% of
respondents completed one to six years of schooling. Most
(79%) were single, but almost 20% were cohabitating with
a partner. Sex work was the main occupation for 37% of
respondents, but 22% had other work (non-sexual), 16%
reported to be unemployed and another 15% reported to be
students. Although about a quarter (26%) lived in their own
apartment or home, most rented an apartment or home
(41%); others rented a room (14%), stayed at a friend’s (10%),
were homeless (5%) or lived in a shelter (3%). In addition,
21% have lived in Mexico City for less than five years. Most
MSWs were primarily street based (working mainly in the
Alameda Central and Zona Rosa neighbourhoods in Mexico
City) (51%), but a smaller number were hotel based and/or
recruited partners via the internet (24%) or were based at
bars and discotheques (24%).
Table 2 presents the baseline results for HIV and STI risk
and prevalence. The mean number of non-paying male sex
partners in the previous week was 2.8; and the mean number
of male clients in the previous week was 4.55. Condoms were
used for 82% of their last commercial encounters, 84% of
their second-to-last commercial encounters, and 78% of
their third-to-last commercial encounters. In 33% of en-
counters, MSWs were the insertive partner; whereas in 27%
of the acts, they were receptive. They were both receptive
and insertive in 17% of the acts. HIV was the most common
prevalent infection (38%), followed by syphilis (21%), chla-
mydia (10%) and active hepatitis B (3%). The less prevalent
STIs were gonorrhoea (2%) and hepatitis C (1%).
Table 3 shows comparisons between self-reported STI and
HIV status versus actual status verified by biological testing.
Of the 100 participants who were confirmed to be HIV-
positive: 14% said they didn’t know if they had HIV, 11% said
they did not have it and an additional 16% said they would
rather not respond. Similarly, of the 86 participants who had
Table 2. Baseline HIV and STI risk and prevalence
HIV and STI risk and prevalence Nn% Mean SD
Number of sexual partners last week
Non-paying male 116 2.76 4.03
Non-paying female 39 2.02 4.00
Male clients 102 4.55 4.98
Female clients 15 2.53 6.03
Condom was used in ...
Last commercial encounter 216 177 81.9 
Second-to-last commercial encounter 202 168 83.7 
Third-to-last commercial encounter 195 153 78.4 
Has ever had HIV test 261 203 77.7 
Knows that healthy-looking person can
transmit HIV
259 227 87.6 
Oral or anal sex with another man before
age 15
232 81 34.9 
First compensated sex before age 15 188 36 19.4 
Body mass index (kg/m
2
) 230 23.8 5.43
Sexual services with last client 139
Penetrative sex 46 33
Receptive sex 37 26.6
Penetrative and receptive sex 23 16.5
Masturbation 31 22.3
Oral sex 74 53.2
Biological test results 267
Active syphilis 55 20.7 
Chlamydia 26 9.81 
Gonorrhoea 6 2.26 
Active hepatitis B 8 3.01 
Hepatitis C 3 1.13 
Has HIV (with confirmatory test) 100 37.7 
Has any STI 85 31.8 
Table presents percentages, unless otherwise noted.
SDstandard deviation; STIsexually transmitted infection and
viral hepatitis (active syphilis, chlamydia, gonorrhoea, and active
hepatitis B and C); Ntotal respondents; nresponses for specific
question.
Table 3. Knowledge of STI and HIV infection versus actual
biological test results
HIV status (test results)
HIV-negative HIV-positive
HIV status (self-report) n%n%
HIV-negative 69 41.3 11 11.0
HIV-positive 0 0.00 59 59.0
Don’t know 36 21.5 14 14.0
Don’t wish to respond 62 37.1 16 16.0
Total 167 100 100 100
STI status (test results)
STI-negative STI-positive
STI status (self-report) n%n%
STI negative 41 22.6 22 25.5
STI positive 10 5.55 7 8.13
Don’t know 34 18.8 14 16.3
Don’t wish to respond 96 53.0 43 50.0
Total 181 100 86 100
Column percentages may not add up to exactly 100 due to rounding.
STIsexually transmitted infection and viral hepatitis (active
syphilis, chlamydia, gonorrhoea, and active hepatitis B and C).
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´rraga O et al. Journal of the International AIDS Society 2014, 17:19218
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any other confirmed STI (other than HIV): 7 (8.13%) said they
did not have any STI, 14 (16.3%) said they didn’t know if
they had an STI and an additional 43 (50%) did not wish to
respond.
Table 4 shows that the median for the highest price
charged for a sexual transaction in the past week was $42.
The median for the lowest price charged last week was $17,
and the median for the average price charged last week was
$25. The median prices charged to the last three clients
ranged from $31 to $33.
Table 5 presents the regressions of the prices paid by
the last client (log transformed) on the primary explanatory
variable, condomless sex, gradually augmenting the model
specification based on the literature. In the first column,
we present the unadjusted coefficient on no-condom-used,
which was 0.332 (pB0.1). Then, in columns 23, we expand
the model and show the adjusted coefficients controlling
for up to 11 covariables. In column 3, the adjusted main
coefficient was 0.345 (pB0.10). Thus, MSWs received a risk
premium of 34.5%; this means that, on average, they got
paid 34.5% higher prices for condomless sex.
Discussion
The results show the rationale for an economic-based HIV
and STI prevention intervention among groups at high risk
of HIV and STI infection in Mexico City. The MSW sample
is generally of low socioeconomic status, with high econo-
mic need, and it shows high levels of risk for HIV and STI
Table 4. Prices charged for commercial sex in the past week and last three clients
Prices charged for commercial sex nMean SD Min Max Median Median (USD)
What was the highest price charged last week? 121 857 1,045 50 8,000 500 42
What was the minimum price charged last week? 121 320 270 50 1,500 200 17
On average, how much did you charge last week? 97 729 1,043 99 6,000 300 25
How much did you charge to your last client? 114 603 756 50 5,500 400 33
How much did you charge to your second-to-last client? 108 515 458 50 3,500 400 33
How much did you charge to your third-to-last client? 96 551 559 50 3,500 375 31
Amounts given in current Mexican pesos (MNX), unless otherwise noted. Last column converts pesos into USD using an exchange rate of 12
pesos/$1 USD.
SDstandard deviation; STIsexually transmitted infection and viral hepatitis (active syphilis, chlamydia, gonorrhoea, and active hepatitis B
and C); USDUS dollars.
Table 5. Baseline regression analysis for the risk premium
Dependent variable: log
(1) (2) (3)
(sex work transaction fee, last client) Coef. SE Coef. SE Coef. SE
Sex work variables
No condom used with the last client 0.332* 0.178 0.385** 0.181 0.345* 0.198
Met client at a hotel 0.337* 0.174 0.215 0.294
Met client on the street or park 0.087 0.153 0.106 0.214
Sociodemographic characteristics
Age 0.141 0.202
Age squared 0.003 0.003
Schooling (ref: 16 years)
79 years 0.448 0.303
1012 years 0.562* 0.312
13 or more years 0.756** 0.336
Marital status (ref: single)
Married/free union 0.697 0.24
Without health insurance 0.237 0.175
Homeless 0.109 0.485
Body mass index (kg/m
2
)0.029 0.222
Constant 6.003*** 0.075 5.841*** 0.143 7.572*** 2.413
Observations 101 96 76
R
2
0.033 0.07 0.204
*** pB0.01, ** pB0.05, * p B0.1; Coef.coefficient; SE standard error.
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´rraga O et al. Journal of the International AIDS Society 2014, 17:19218
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transmission and acquisition, as evidenced by high prevalence
for HIV (38%) and high prevalence for other STIs (32%),
important levels of condomless sex (17%) and multiple sex
partners (about five male clients and three non-paying
partners per week). Moreover, we found evidence of a
risk premium in the commercial sex transaction prices:
MSWs received more money (35% higher prices) to engage
in condomless sex. Thus, the economic rationale to provide
financial incentives to increase protection seems well justified.
Of the 100 participants who were living with HIV at
baseline, 41% did not know that they were HIV infected or
declined to self-report their status (Table 3). Given the high
number of sexual partners (over 250 per year) and the rates
of condomless sex, the implied potential transmission rates
constitute a public health concern [33]. Economic incentives
may be an avenue to attract MSWs to screening and medical
care in an HIV and STI clinic with a team specifically dedicated
to this key population. An intervention with incentives is an
important avenue to facilitate access to screening and treat-
ment services in a population who otherwise might not accept
or access these services. Similarly, of the participants who
knew they were living with HIV, only 40% were on treatment;
and, of those, only 61% achieved viral suppression. Thus,
interventions to improve access and adherence to antiretro-
viral therapy (ART) among MSWs living with HIV are also
warranted, including, possibly, incentives for linkage to care
and viral suppression. This seems particularly feasible in a
country such as Mexico, which has universal access to ART;
participants at Clı
´nica Condesa have access to ART (free
to them) provided through Seguro Popular (the social health
insurance programme for those without employer-based
insurance coverage).
The extant results show that enrolment of a cohort of
MSWs is feasible in the context of HIV and STI prevention in
Mexico City, and that Punto Seguro is a culturally appropriate
intervention in the local context. Furthermore, in terms of
HIV prevalence and risk, our cohort seems to be a population
at even higher risk than the average MSW population found
in a recent population survey [2,3], although this may be
explained in part because of the active recruitment within a
clinical site (Clı
´nica Condesa).
Because economic need has been identified as an impor-
tant reason for engaging in sex work and an important barrier
to using condoms consistently, our pilot project will test
the potential efficacy of a public health and behavioural eco-
nomics intervention to reduce HIV and STI risk and vulner-
ability among MSWs in Mexico City. The baseline results
presented here confirm previous formative work in which
we asked MSWs to endorse the incentive levels necessary
for behaviour change ($156/year) [28]; this would represent,
on average, trying to avoid unprotected sex with about six
clients over a year. Nevertheless, our method to estimate the
acceptable incentive may have captured what participants
wanted to receive to commit to attending regular visits for
testing, and it may not fully reflect a compensation to avoid
the risk premium. As such, some corrections would be needed
in the willingness-to-accept estimates before implementing
a trial.
Furthermore, the benefits may last longer than the inter-
vention itself because of three main mechanisms at work.
First, an MSW who is negative for HIV and STIs, and is
using condoms consistently, will likely remain free of infection.
Second, an MSW who is positive for HIV and STIs, and is using
condoms consistently, is much less likely to transmit HIV
and STIs to sexual partners. Third, an MSW who is positive for
HIV, has linked to medical care and ART and has achieved
virologic suppression is also much less likely to transmit HIV
to partners [34]. This would result in fewer new cases of
HIV. Intervention with economic incentives may thus work
well as a bridge to help MSWs to link to HIV care and
ART. Moreover, it is likely that if the financial incentives are
stopped, the participants will have already developed other
links to the clinic and start receiving other types of positive
outcomes (health, psychological, social etc.) from the care
team, so that MSWs may continue their ART and/or follow-up
with prevention reduction (both HIV-positive and -negative),
regardless of the continuity of economic incentives. We
acknowledge, nevertheless, that staying free of new curable
STIs may contribute to staying HIV-negative, and it can be
another incentive among those who are HIV-negative but not
those who are already HIV-positive. The differences across
HIV serostatus need to be taken into account in this type
of incentive programme. In theory, the motivation to protect
sexual partners from infection may differ along a continuum
of altruistic intentions. Stratified analyses are needed in
future trials to empirically test for differential effects by HIV
serostatus.
The study has limitations. First, the relatively limited sample
size leads to results for the risk premium which are only
borderline significant. Second, the incentives for behaviour
change may be small given that the risk premium for MSWs,
of about 35%, is higher than what we originally hypothesized
based on the previous literature, at levels closer to those
observed among female sex workers: 923% [24,25,35].
Third, the relative ease with which A-CASI allows participants
to refuse to answer, or simply skip ahead to the next question,
led to several key variables with missing values. Despite these
limitations, the current study shows that we have been able
to enrol a substantial number of participants from a key
population for which only limited research exists, usually with
smaller samples and shorter follow-up periods [36].
Conclusions
This article provides a strong rationale for the adaptation of
an economic incentives intervention for male sex workers in
the context of HIV and STI prevention. This first evidence of
higher payments for unprotected sex in the male commercial
sex market in Mexico is also consistent with the justification
for using cash transfers to incent HIV risk reductions through
STI screening visits as a means to counteract the market-
based inducements to engage in behaviours that are more
likely to transmit HIV in this heavily affected population.
The Punto Seguro pilot trial has recruited MSWs, and it is
an example of an economic-based HIV prevention intervention
targeted to the populations who are most at risk in concen-
trated epidemic settings. As demonstrated by these initial
results, this type of intervention seems to be well justified, and
Gala
´rraga O et al. Journal of the International AIDS Society 2014, 17:19218
http://www.jiasociety.org /index.php/jias/article/view/19218 | http://dx.doi.org/10.7448/IAS.17.1.19218
6

it should continue to be explored in the context of combina-
tion prevention efforts for key affected populations.
Authors’ affiliations
1
Brown University School of Public Health, Providence, RI, USA;
2
Instituto
Nacional de Salud Pu
´blica (INSP), Cuernavaca, Mexico;
3
Clı
´nica Especializada
Condesa, Mexico City, Mexico;
4
Psychiatry and Mental Health, University of
Cape Town, Cape Town, South Africa;
5
The Fenway Institute, Beth Israel
Deaconess Medical Center, Boston, MA, USA;
6
Harvard Medical School,
Boston, MA, USA
Competing interests
The authors declare that they have no competing interests.
Author’s contributions
OG and SGSR developed the original idea to conduct a randomized control
pilot. OG, SGSR, AG, DO, CK and KHM developed the methods for the trial
and for completion of data collection. SBA, FBH, CJCG and LJF contributed to
developing the methods, developing data collection protocols for baseline, and
revising the report. OG and SGSR conducted data analysis, and they drafted
and revised the manuscript with comments from all authors. All authors have
read and approved the final version.
Acknowledgements
We thank useful comments from Stefano Bertozzi, Will Dow, Damien de Walque,
Juan Carlos Montoy, Manisha Shah, Harsha Thirumurthi, Kristen Underhill, Justin
White and participants at the International Health Economics Association (iHEA)
meetings in Sydney, Australia, and at the Population Association of America
(PAA) meetings in San Francisco, California, USA. We gratefully acknowledge
all the Punto Seguro staff members, particularly Nathalie Gras, Octavio Parra
and Jehovani Tena; as well as the devoted medical staff, particularly Dr Arturo
Martı
´nez Orozco. Biani Saavedra, Fernando Ruiz and Cecilia Hipo
´lito provided
research assistance; Marı
´a Olamendi and Santa Garcı
´a conducted the polymer-
ase chain reaction diagnosis of chlamydia and gonococcus in urine samples.
The Consortium for HIV/AIDS Research (CISIDAT, A.C.) provided project manage-
ment and administration support. We especially thank the participants for
agreeing to become part of Punto Seguro.
Funding
US National Institutes of Health (R21HD065525; ‘‘Conditional economic
incentives to reduce HIV risk: A pilot in Mexico’’; PI: Gala
´rraga O.) with
additional support provided to C. Kuo (K01 MH096646-01A1); and the
Mexican National Centre for HIV/AIDS Control and Prevention (CENSIDA:
Proy-2014-0262).
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