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Pre-exposure prophylaxis (PrEP) is highly effective at preventing HIV but it does not protect against sexually transmitted infections (STIs). There is concern that there may be an increase in condomless sex among PrEP users which could lead to an increase in STIs. This has fuelled a debate about whether PrEP use might propel the STI epidemic in gay, bisexual and other men who have sex with men (gbMSM). However, the recommended practice for all people on PrEP includes regular STI testing and treatment which should result in earlier detection and treatment of STIs. This might lead to a reduced burden of STIs despite potentially increasing rates of condomless sex. This article will review the ways in which PrEP could help or hinder STI prevention efforts among gbMSM.

What is PrEP and how is it fueling a debate about STIs?

Pre-exposure prophylaxis (PrEP) is a combination of two medications taken by people who are HIV negative to prevent them from getting HIV. Besides taking pills, taking PrEP also involves visiting a doctor or nurse every three months for HIV and STI testing, receiving risk reduction counselling, and being monitored for drug side effects. Anyone who is at high risk of getting HIV can take PrEP, regardless of their gender or sexual orientation. However, in Canada and other high-income countries, many people who take PrEP are gbMSM.

Condoms have been the cornerstone of HIV prevention around the world since the 1980s. But amid declining rates of condom use over the past two decades, there have been increasing rates of STIs among gbMSM (and in Canada overall).1 PrEP represents a major breakthrough in HIV prevention because it provides an alternative HIV prevention option to condoms.

While there is no question that PrEP is effective at preventing HIV, the medications used in PrEP, unlike condoms, do not protect against STIs such as chlamydia and gonorrhea. Questions have been raised about the effect that PrEP use among gbMSM may have on the already high rates of STIs in the community if PrEP is used without condoms.

How can PrEP help or hinder STI prevention?

There are two main ways to help prevent the spread of STIs – individual behavioural change and STI testing and treatment. Behaviour change includes any actions that an individual can take to lower the chance of getting or passing an STI, such as using condoms or having fewer sex partners. STI testing and treatment involves routinely offering testing to individuals at risk for STIs and offering prompt treatment to clear or manage any STIs. Routine testing is important because many STIs can be asymptomatic and individuals are likely to pass the STI to others without even knowing they have an infection.  

PrEP has the potential to impact STI transmission by influencing individual behaviour and the frequency of STI testing and treatment. In terms of behavioural change, there is a concern that once people start taking PrEP they may choose to use condoms less often, or have condomless sex with more partners because they no longer worry about HIV. This is a concept known as risk compensation.2 If this happens, then the risk for STIs would increase in people taking PrEP compared to before they started taking PrEP. However, according to the Canadian PrEP guidelines, people taking PrEP should receive risk-reduction counselling which could mitigate this issue by encouraging individuals to use condoms more often or to lower their STI risk in other ways, such as having fewer partners.

The frequency of routine STI testing and treatment that accompanies PrEP has the potential to reduce the spread of STIs among gbMSM. The Canadian PrEP guidelines recommend STI testing at screening for PrEP, 30 days after the start of PrEP and then every three months.3 People who are eligible for PrEP are often at high risk for STIs, as many of the behaviours that put a person at risk for HIV also put them at risk for other STIs. PrEP represents an important opportunity to test and treat STIs in people who are at high risk. If individuals receive prompt testing and treatment, their chance of passing STIs onto others is greatly reduced. If these individuals were not taking PrEP, they may not have received STI testing as frequently or at all, and their chance of passing STIs onto others would be much greater.

Does research show that gbMSM take more risks when they start using PrEP?*

A 2018 systematic review included 13 studies that looked at the connection between PrEP use and STI risk behaviours among gbMSM.4 Most of the studies that were included in the review found little evidence of risk compensation with very little change in gbMSM’s sexual risk behaviour before and after taking PrEP. A few studies did find some sexual risk indicators that increased significantly and one study found a significant decrease in risky sexual behaviours. These mixed results show that the relationship between PrEP use and risk behaviour is complex, and that PrEP use does not always lead to an increase in condomless sex.

Of the studies that found a significant increase in sexual risk behaviour, the difference between behaviours before and after starting PrEP tended to be fairly small.4 For example, one study of gbMSM on PrEP found a significant increase in condomless sex with casual partners who were either HIV positive or whose HIV status was not known.5 In this study condomless sex was already high (80%) before starting PrEP, and increased to 91% at 12 months on PrEP. Another study found that the proportion of people who reported never using condoms in the past 30 days increased from 10% at the start of PrEP to 24% at the nine-month follow-up PrEP visit.6

In addition to the studies that found a significant increase in sexual risk behaviour, some studies found no change in sexual risk behaviours and one study found a significant decrease in sexual risk behaviour.4 In the study that found a significant decrease in risk behaviour, 34% of gbMSM reported having condomless receptive anal sex at the start of PrEP, and only 25% reported doing so after starting PrEP.7 Most of the studies found that the average number of sex partners did not increase after starting PrEP.4

What is involved in deciding to use condoms while taking PrEP?

Qualitative interviews help us to understand gbMSM’s decisions around condom use when taking PrEP. A qualitative study done in New York City looked at risk compensation and found that gbMSM were aware that their risk for STIs would increase if they used condoms less often.8 However, some said that without fear of contracting HIV, they were more willing to accept a risk for other STIs. Others expressed that they continue to use condoms in situations where they think that there may be a substantial risk for STIs.  

One important factor that appears to influence the decision-making around condom use is the quality of risk reduction counselling that is provided alongside PrEP. In a study that found a decrease in condomless receptive anal sex in PrEP users, participants received a discussion-based form of counselling called integrated next-step counselling.7 This study suggests that providing high-quality counselling along with PrEP has the potential to reduce STI risk behaviour.

Are STI rates rising in people who take PrEP?

Besides looking at risk behaviour, the 2018 systematic review also included eight studies that looked directly at the connection between PrEP use and STI diagnoses.4 Two of those studies found that STI incidence increased significantly after participants started taking PrEP.9,10 The other six studies did not find that PrEP use was associated with a significant increase in STIs. Together, these studies suggest that PrEP use increases STI rates in some cases, but not always.

The review also combined the results from these eight studies in a meta-analysis, to see if there was a trend of increasing STI rates overall. The combined results found that when gbMSM started taking PrEP, they were 1.24 times more likely to get an STI compared to before they started taking PrEP.4 This is a modest but significant increase, suggesting that STI rates are increasing somewhat among PrEP users overall.  However, it’s important to note that in some of these studies, part of the reason for this increase could be that people received STI testing more often once they started taking PrEP.

The review also included a separate analysis with six studies that were published from 2016 onwards.4 This included the two studies that found a significant increase in STIs because both were published during this timeframe. The combined results found that when gbMSM started taking PrEP after 2016 they were 1.47 times more likely to get an STI once they started taking PrEP. The researchers suggest that this could be because over time people are starting to have more confidence in PrEP as an HIV prevention strategy, and they may be using condoms less as a result. 

Will testing and treatment help to lower STI rates among gbMSM in the long-term?

A modelling study from the United States suggests that PrEP use might actually help to lower STI rates among gbMSM over time because people on PrEP would receive frequent STI testing and treatment, and thus reduce their risk of transmitting STIs to others.11 The study predicted the effect that PrEP might have on STI incidence among 10,000 gbMSM in the United States over the course of 10 years, taking into account risk compensation as well as the impact of regular STI testing and treatment. The study used a sophisticated model to predict how chlamydia and gonorrhea would spread among social networks. The model assumed that:

  • PrEP was being taken by 40% of gbMSM who were eligible to take it
  • There was a 40% decrease in condom use among men taking PrEP
  • Each man received STI screening every six months and received treatment to clear any STIs

The study estimated that over 10 years in this scenario, 42% of gonorrhea infections and 40% of chlamydia infections would be prevented. Thus, even if risk behaviours increased quite substantially, the model predicted that the net effect over the long-term would be a decrease in STI incidence among gbMSM. This reduction was among all gbMSM in the population, not just those taking PrEP. While the model is sophisticated, it likely does not fully account for some of the complex factors that would impact STI incidence in the real world (for example, strains of gonorrhea that are resistant to medications). Nonetheless, the study provides compelling evidence to suggest that PrEP use could actually help to manage the spread of STIs in the long-term through regularly testing for and treating STIs.

For this benefit to be realized, it is important for gbMSM to receive STI testing at all potential sites of infection. The Canadian PrEP guidelines recommend testing for gonorrhea and chlamydia with a urine test, as well as testing at anatomic sites depending on the types of sexual activity.3 This means that men who are at risk through oral sex should be tested with a throat swab, and those at risk through receptive anal sex should receive a rectal swab. The guideline also recommends testing for syphilis, which is done through a blood test.3 To detect asymptomatic STIs in gbMSM, it is important that these tests are conducted routinely.

Research into STI testing patterns in gbMSM has shown that doctors commonly test for gonorrhea and chlamydia with a urine test, but many do not perform throat and rectal swabs.12 This is problematic because a urine test can only detect urethral gonorrhea and chlamydia, and many gbMSM are at risk for infection in the throat or rectum. One study estimated that over 80% of chlamydia and gonorrhea infections in gbMSM would go undetected if they only received a urine test.13

Research into STI testing patterns in gbMSM on PrEP show a similar pattern of missed STI testing. A study in New York City looked at the counselling services and tests that were given to 104 gbMSM who were taking PrEP.14 They found at their last clinic visit, most men had blood drawn (94%) and provided a urine sample (88%). However, only about half received oral swabs (48%) and rectal swabs (51%) at their last visit. It is possible that some of the men did not require all of these tests (for example a man who did not have receptive anal sex would not need a rectal swab). However, 23% of participants were not asked about their sexual behaviours, and the doctor would not have been able to determine what tests were needed in those cases. When healthcare providers do not test for STIs at all relevant sites, STIs may go undetected.

What can service providers do to help manage STIs among gbMSM taking PrEP?

The Pan-Canadian STBBI (sexually transmitted and blood-borne infections) framework for action provides a vision, strategic goals and guiding principles to support action to address STBBIs in Canada.15 The framework emphasizes that many STBBIs share routes of transmission, as well as populations that are most affected. Therefore, it recommends that efforts to address different STBBI should be integrated with one another. This framework is useful for thinking about STI management in the context of gbMSM who take PrEP. We know that gbMSM are disproportionately affected by HIV as well as other STIs, and that many of the behaviours that put a person at risk for HIV also pose a risk for other STIs. Within this framework, rather than thinking of PrEP as a tool that helps to prevent HIV at the expense of efforts to prevent other STIs, PrEP can be thought of as an integrated care model that can help to prevent HIV as well as other STIs. Looking at the framework’s three strategic goals can help to inform work in this area.

Strategic goal #1: Reduce the incidence of STBBIs in Canada

PrEP provides an opportunity to engage with gbMSM who may be at high risk for STIs. gbMSM who are taking PrEP should be made aware that PrEP, though highly effective for preventing HIV, does not protect against other STIs. They should also be informed about other risk-reduction strategies that are available to them (including condoms), and the importance of regular STI testing and treatment.

Strategic goal #2: Increase access to testing, treatment, and ongoing care and support

Service providers can play a role in ensuring that gbMSM who are taking PrEP receive appropriate STI testing and treatment. This can be done by educating clients about the types of tests that they should receive so that they can ask for the appropriate tests at medical visits. In particular, gbMSM should be made aware that rectal and oral swabs are often necessary.

Strategic goal #3: Reduce stigma and discrimination that create vulnerabilities to STBBI

The framework recognizes systemic stigma on the basis of sexual orientation as a factor that plays a role in STBBI vulnerability. Working with gbMSM, it is very important that risk-reduction information is presented in a manner that is sex-positive, so that the person feels comfortable talking honestly about their risk behaviours. Service providers should recognize that PrEP is intended for people who are already engaging in high-risk sexual activities, including condomless sex, so it would likely be unrealistic to expect that people will start to use condoms consistently when they start taking PrEP. Ultimately, each individual has a right to make informed decisions about their own sexual health.

Resources for gbMSM

The Sex You Want: PrEP  - Gay Men’s Sexual Health Alliance (GMSH)

8 Questions about PrEP for Guys - CATIE

Resources for service providers & healthcare workers

Oral pre-exposure prophylaxis (PrEP) – CATIE fact sheet

Canadian Guideline on HIV Pre-Exposure Prophylaxis and Nonoccupational Postexposure Prophylaxis

Pre-exposure prophylaxis (PrEP) resources

Reducing the health impact of sexually transmitted and blood-borne infections in Canada by 2030: A pan-Canadian STBBI framework for action – Government of Canada

*Many of the studies cited in this article include a small number of trans women who have sex with men as well as gbMSM. Some findings may apply to trans women, but it is difficult to make conclusions because of the small number of trans participants. For more information on PrEP for trans people see PrEP for understudied populations: Exploring questions about efficacy and safety.



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About the author(s)

Mallory Harrigan is CATIE's Knowledge Specialist, HIV Prevention. She has a Master's degree in Community Psychology from Wilfrid Laurier University.