The last comprehensive review about the Epidemiology of HIV in Latin America was published in 2008. It underscored the concentrated aspect of the epidemic in most of the countries, especially among MSM . In a recently published review of HIV prevalence data through 2010 of MSM and female sex workers (FSW) from Latin America and the Caribbean (LAC), the estimated median prevalence among MSM (10.6%) was reported to be five times higher than that of FSW [2▪]. The aim of this review is to provide an update on HIV/AIDS Epidemiology in LAC by addressing studies published since 2011 and providing the highlights related to key populations.
The HIV epidemic is not homogenous across the Latin America and Caribbean countries. In 2012, 1.5 million adults and children were estimated to be living with HIV in Latin America, with a stable prevalence ranging from 0.2% in Mexico to 0.7% in Guatemala, Panama and Uruguay (Table 1). In the same year, the Caribbean had 250 000 individuals living with HIV, but still had one of the highest HIV prevalence rates in the world with estimates for the general population ranging from less than 0.1% in Cuba to around 3% in the Bahamas [3▪]. In three of the five highest populated Caribbean countries, women outnumbered men among adults living with HIV .
With respect to mother-to-child transmission (MTCT), many of the countries have incomplete estimates, often with large confidence intervals (Table 1), which indicates that further improvement of national surveillance systems are still needed. Efforts to obtain data on underrepresented populations, as the study conducted among six native populations from the Peruvian Amazon , may also be important to identify other populations that may be at risk. Despite these limitations, 2012 data from the Caribbean showed a remarkable increase in the combined antiretroviral treatment (cART) coverage for pregnant women living with HIV, approaching an overall 79% coverage [3▪].
Over the period of 2005–2012, increased cART coverage resulted in a substantial reduction in mortality from AIDS-related causes, specifically, a greater than 25% decrease in the Bahamas and Haiti, and a greater than 50% reduction in the Dominican Republic [6,7]. As people live longer, HIV prevalence and AIDS cases reporting are less effective at monitoring rapid epidemic changes [8,9], but estimating incidence rates remains challenging . Mostly, LAC incidence data come from the Joint United Nations Program on HIV/AIDS estimates, which indicate that, for the 2001–2012 period, new cases remained stable in Latin America and had a pronounced decline (49%) in the Caribbean [3▪].
Although there is progress on the use of novel HIV infection surveillance approaches, these initiatives remain fragmented and limit the usefulness of the information for program planning and evaluation. Incidence studies using BED-capture enzyme immunoassays and studies addressing phylogenetic mapping have increased [11–13]. Some approaches, aimed to identify transmission networks, have combined techniques to reach hidden populations with molecular epidemiology such as the one conducted in El Salvador with MSM and FSW using respondent-driven sampling (RDS) . Advances in monitoring transmitted drug resistance (TDR) were also made, and are increasingly important to guide the selection and rational use of cART in the region, as low-to-moderate TDR  has been identified in several countries .
The methods to estimate prevalence of HIV infection among hard-to-reach populations, as well as the size of the key populations, are in constant advance and its discussion is beyond the scope of this manuscript. Efforts to implement some probabilistic approach have been made in LAC, and researchers have increased the use of RDS, as described by Montealegre et al. review . However, many of the reviewed studies were not published as scientific articles and others may have a 5-year gap between data collection and publication, possibly because of a low number of data analyses resources. Additionally, information from MSM, FSW and IDU tends to be restricted to major cities or areas where HIV/AIDS prevalence is elevated; therefore, caution must be made when making generalizations.
MSM are vulnerable population for HIV and prevalence rates were still increasing worldwide in 2012 [18▪]. Most of the new HIV cases in LAC occur among MSM ; in Jamaica, HIV point prevalence among this population was estimated to be as high as 37.6% (Fig. 1) [3▪].
The largest study of MSM (n = 3859) using RDS in LAC was conducted across 10 Brazilian cities and estimated that HIV prevalence ranged from 9.1 to 16.6% . In El Salvador, HIV prevalence among MSM was 10.8% (95%; CI 7.4–14.7%), 21% of these individuals were diagnosed as being recently infected. The young MSM (15–24 years) in this population were three times more likely to be a recent infection than the older MSM .
A study conducted in Argentina (RDS, n = 500) estimated an incidence rate of 5.6 per 100 person-year among MSM who only had sexual contact with other men, and an incidence of 4.28 per 100 person-year among MSM who also have sexual intercourse with women (P = 0.032). The first group also had a higher prevalence of HBV, Treponema pallidum and human papillomavirus indicating that interventions for preventing HIV and sexually transmitted diseases transmission should consider differences in sexual partnership .
Few studies have evaluated the main transmission networks among MSM from LAC. A mathematical model of the USA and Peru estimated that between 4 and 30% of HIV transmission events (depending on the parameter model) result from contacts with an acutely infected partner, and around 30% of infections occur with main partners . In two cities from El Salvador, San Salvador and San Miguel, 34.9 and 58.8% of interviewed MSM reported bisexual behavior in the 12 months before the interview . Overall, inconsistent condom use was reported by 51.7% of MSM who also had sex with women and by 60.2% of MSM who only had sex with men (P = 0.13). Besides the understanding of HIV transmission among MSM networks, this information is critical to better understand the ‘bridging’ of HIV transmission among MSM and females, and for proposing specific/targeted prevention strategies for those in stable relationships.
Unprotected anal intercourse (UAI) is the main transmission route in this population, and factors such as the use of illicit drugs, having a stable male partner and psychological abuse have been associated with increased UAI frequency in the aforementioned studies [25,26]. Of note, 40–70% of MSM enrolled in studies conducted in the region had never been tested for HIV [21,20,25,24], indicating that targeted strategies for locating and testing this population are urgently needed. Furthermore, investigation into the low testing rates was performed in Peru using an Internet-based survey. The survey results showed that the primary reasons for MSM to not be tested were the fear of a positive result and not knowing where to be tested .
Previous research have suggested that populations included in RDS and time-location sampling (TLS) studies may have different characteristics, with the former most frequently enrolling individuals with lower educational and income levels . In accordance with that, a study using TLS conducted in Mexico City (n = 3000) approached MSM at gathering places (clubs, bars, streets) and produced estimates for a population of 6000–14 000 MSM. They had a higher education and socio-economical level than the average population, and yet more than 30% of the respondents had never been tested for HIV .
Transgender women (TGW) are individuals assigned as ‘male’ at birth but who identify themselves as female and/or transgender. Although they represent a smaller population than MSM, TGW have extremely elevated HIV infection rates. A meta-analysis across 15 countries (10 were low-and middle-income countries and five of those in LAC) estimated an HIV prevalence of 17.7% (95%; CI 15.6–19.8) in this population, with an odds ratio (OR) of 50.0 (95%; CI 26.5–94.3) for HIV infection among TGW versus all adults in reproductive age in LMIC [30▪].
TGW represent the most heavily impacted population in Peru, with an overall HIV point prevalence of 30% . Risks associated with HIV infection among TGW are mainly linked to high rates of sex work, limited formal education, irregular use of condoms and drug abuse, coupled with extreme marginalization and lack of other options for survival [32,33,35]. Social exclusion and violence are factors that contribute to increased vulnerability and limitations on access to care and prevention. In fact, a study conducted in Argentina showed that TGW sex workers had the highest incidence rate (11.3 per 100 person-year) ever described in the country .
Studies to understand HIV transmission, associated behavior and health needs of TGW are as rare in LAC as in other parts of the world, and the use of qualitative–quantitative approaches and triangulation methods could be very promising in achieving this intent.
FEMALE SEX WORKERS
In a meta-analysis, the prevalence of HIV among FSW from 11 LAC countries was estimated at 6.1% (95%; CI 5.7–6.6); the odds of being HIV positive were 12 times higher than that of women from the general population. However, there was great variability within the LAC region. For example, in Chile, FSW had 0.29 (0.02–4.64) times the odds of the female population; in Guyana, the OR was 25.26 (20.47–31.17) .
Variability of within country prevalence estimates was also observed. For example, in Brazil, prevalence was 1.8% for FSW from Goiás , 4.8% in a study conducted in 10 Brazilian cities  and 5.1% in a systematic review . Intracountry differences may be because of the actual different prevalence rates among the cities, socio-cultural aspects and methods used to sample the target population as well as to estimate the rates. Most studies use convenience samples , but there is also an increase in the use of RDS  and TLS . A study conducted in Peru has used a probability sample combined with a venue-based sample and estimate 0.5% HIV prevalence among this population .
Many uncertainties persist related to the use of condoms with stable partners and drug use, but data from behavioral surveys suggest that the knowledge about HIV transmission and the efficacy of preventive measures seem to be increasing among FSW. Longer periods of prostitution, discounted rates for performing sex acts and association with other STD  are three key factors associated with increased risk of HIV infection in the FSW population. Among FSW in an Argentinean study, being socially rejected because of sex work and being arrested were both associated with an increased chance of being HIV positive .
Unlike MSM, TGW and FSW, the number of studies including IDU from LAC has decreased in recent years. This reduction may be associated with the revised estimates of IDU prevalence (0.45% (95%; CI 0.31–0.61)) and HIV prevalence among IDU (6.9%) in LAC . However, in Mexico especially along the United States border, an increasing IDU prevalence was reported, sometimes in association with sex work [45,46]. These trends were observed via epidemiological studies not through general surveillance data. Therefore, it is important that we continue to investigate and report on IDU, as most of the manuscripts included in this review do not capture this information.
Noninjecting drug use (NIDU) is indirectly associated with HIV by increasing sexual risk behavior, and studies have associated NIDU with increasing chance of HIV among MSM, TGW and FSW [47,48]. In Peru, problem drinking was associated with an increase in risky sexual behavior in the MSM population , but few studies have approached alcohol influence on HIV transmission and the impact of alcohol use may be underestimated in LAC.
Limited data on HIV prevalence for NIDU are available beyond 2011. A study conducted in Tijuana (Mexico) with a convenience sample of 164 NIDU (who were neither MSM nor FSW), found an overall HIV prevalence of 3.7% (similar to IDU which was 4%) and only 36% of NIDU reported having previously been tested for HIV . Given the increase in cocaine/crack-cocaine availability observed in some LAC countries , and anecdotal results pointing to an association between crack cocaine and HIV (mediated by sexual behavior/exchanges between sex drugs), this population should be kept under surveillance.
Considering the aforementioned, many advances were made in order to achieve the Millennium Goals and an ‘AIDS-free’ generation. The results from the HPTN 052 study  successfully demonstrated that treatment is an effective prevention measure with a profound impact in public health. As a result, the increased cART coverage in LAC countries in recent years has likely contributed to the control of the epidemic. A Pan American Health Organization (PAHO) report estimated that mean cART coverage in the region is at 63%; four countries (Chile, Cuba, Guyana and Nicaragua) are considered as having universal access to treatment (more than 80% coverage). Countries with high coverage also have higher retention rates for follow-up care, which is essential for the achievement of undetectable viral loads. The continued provision of treatment and even higher increases in coverage are new challenges for the LAC's health systems and governments, as regional per-patient cost of ART is US$508 annually (US$232–3323) and almost a third of the countries are highly dependent on international sources for funding [52▪].
Arán-Matero et al. have estimated that 79% of public spending on HIV/AIDS in LAC is devoted to treatment initiatives whereas prevention efforts received 15% of total funds. Interventions and programs to prevent the HIV expansion among key populations represented only 4% of prevention expenditures. Incredible progress has been made in the HIV prevention field during the last few years, and most at risk populations may benefit from the addition of strategies such as postexposure prophylaxis and pre-exposure prophylaxis (PrEP) to the already existing prevention strategies . In fact, a mathematical model of the MSM population from Lima have showed that the use of PrEP would be cost effective for preventing HIV infection at a population level in the city if it could be implemented as an integrated approach, prioritizing high-risk MSM and TGW .
With estimates of up to 50% of HIV-positive individuals in LAC being unaware of their serostatus, strides must be made to increase testing and prompt linkage to care. Culturally sensitive strategies to access hard to reach individuals, refer them to testing, link them to care and treatment, and retain them in the health services are highly needed in LAC. Moreover, novel and creative strategies are needed to inspire health practitioners and their clients.
Last but not the least, social inequalities, discrimination and violence pervade the HIV epidemic among key populations from LAC and undermine the efforts for identifying, testing and linking individuals to care. Even though there is a huge difference in socio-cultural characteristics across countries, there are still inequalities and traditional values that may act as barriers for HIV prevention and reinforce stigma among high-risk populations. Interventions that address these issues may have a higher chance of success , especially if focused on high-risk groups.
The authors would like to thank Carolyn Yanavich for the valuable comments.
Conflicts of interest
B.G. would like to thank FAPERJ and CNPq for long-term funding.
The authors have no conflicts of interest to declare.
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