22 September 2015 

PrEP in the community—an observational study finds very encouraging results

Clinical trials have demonstrated that taking anti-HIV drugs regularly prior to sexual encounters can significantly reduce a person’s risk for acquiring HIV infection. Taking medicines in this way is called pre-exposure prophylaxis (PrEP). The medicines used for PrEP are found inside a fixed-dose combination—tenofovir + FTC—sold as a single pill called Truvada.

Analyses of published clinical trials have found that taking Truvada every day exactly as directed can provide a high degree of protection from HIV.

Inside a clinical trial, participants are monitored, undergo regular doctor’s visits, have their blood analysed and are encouraged to take PrEP. In many fields of medicine, drugs perform well in clinical trials but are somewhat less effective once they are licensed and used by ordinary people in the community. In part, this issue arises because not all people take their medicines exactly as directed. Therefore, there are concerns that some people prescribed PrEP in the everyday world outside of a clinical trial might not take it every day and that their risk for HIV might rise as a result.

New data from an observational study about PrEP in San Francisco are very encouraging. In a report from the health maintenance organization Kaiser Permanente that focussed on 657 people, researchers found that no new cases of HIV occurred. It is important to bear in mind that these people were part of a dedicated PrEP program. However, the study does underscore the extremely promising results that can occur when such programs are well resourced and implemented in the community.

Study details

According to the research team, Kaiser Permanente is “a large integrated healthcare system that provides comprehensive medical services to over 170,000 adult residents of San Francisco.”

For the present study, researchers assessed health-related information on patients within the Kaiser system between July 2012 and February 2015.

In the Kaiser system, healthcare providers assess patients who are at high risk for HIV and/or who have requested PrEP and then refer them to a dedicated PrEP program. This program provides a range of services including the following:

  • adherence support
  • clinical monitoring
  • access to specialists in the following fields—infectious diseases, nursing and pharmacy

Prior to receiving PrEP, patients undergo comprehensive screening to unmask any pre-existing health issues, such as the following:

  • HIV infection
  • other sexually transmitted infections
  • thinner-than-normal bones

Once PrEP is prescribed and initiated, repeated screenings are done every “one to three months,” according to the researchers.

Although 1,045 people were referred to the PrEP program, not all were prescribed PrEP. Ultimately, a total of 657 (63%) people initiated this form of HIV prevention.

The average profile of these 657 people when they initiated PrEP was as follows:

  • age – 37 years
  • 653 (99%) were men who have sex with men (MSM), three were women and one was a transgender man who had sex with men
  • one person disclosed injecting street drugs
  • 15 people disclosed having previously used HIV post-exposure prophylaxis (PEP)


Researchers found that people who initiated PrEP, compared to people who did not, were more likely to report the following:

  • multiple sex partners
  • previous use of PEP from a doctor outside of the Kaiser healthcare system

People who did not initiate PrEP were more likely not to disclose any behaviours that would have placed them at high risk for HIV.

Reasons for not using PrEP

People who did not initiate PrEP gave one or more of the following reasons that underpinned their decision-making:

  • they were at low risk for HIV
  • concern about the high cost of Truvada
  • they did not wish to undergo the relatively frequent doctor’s appointments and lab testing that are a necessary part of using PrEP
  • preferred to use PEP to prevent HIV
  • concern about the potential side effects of Truvada

According to the researchers, only a few people had medical reasons that would have rendered PrEP unsuitable for them, such as the following:

  • previously undiagnosed HIV infection – 3%
  • kidney dysfunction – 1%
  • severely thin bones – 1%

Sexually transmitted infections (STIs)

Among the 657 people who initiated PrEP, researchers found that 187 were “diagnosed with at least one STI” over the course of the study. Researchers also found that 78 people were “diagnosed with multiple STIs,” as many as two to 10 STIs per person in some cases. Altogether, a total of 344 STI diagnoses were made over the course of the study.

Relatively common STIs that were diagnosed included the following:

  • Chlamydia
  • gonorrhea
  • syphilis

STIs over time

Over the first six months of the study, after participants had initiated PrEP, 30% were diagnosed with an STI. After 12 months of using PrEP, 50% of participants had been diagnosed with an STI.

Protection from HIV

The average time spent on PrEP was seven months. During this period, there were no new HIV infections diagnosed among PrEP users. When researchers focussed on participants who took PrEP for 12 months, they also did not find any new HIV infections.

Bear in mind

Good news

The results from the Kaiser study show that people at high risk for HIV are able to make effective use of PrEP when it is offered as part of a dedicated program. While no new HIV infections were diagnosed among PrEP users in this study, it is important to bear in mind that this was not a randomized clinical trial. Although the results are encouraging, there was no formal control or comparison group. Therefore, one cannot draw robust conclusions about the effectiveness of PrEP from the Kaiser study as there are unmeasured factors that could have confounded or affected the study’s results.

Some potential sources of confounding

The researchers noted that there were factors related to the study’s location—San Francisco—that could have affected their results. For instance, a relatively high proportion of MSM in San Francisco have HIV, but many are also taking ART and thus have a viral load that is less than 50 copies/ml. Given the widespread use of ART and high number of low viral loads, participants may generally have been at lower risk for HIV than if the study had taken place in a city or region where ART is less widely used and viral loads are generally higher.

However, based on the results—no new HIV infections were diagnosed—the Kaiser study is very encouraging.

Don’t forget about STIs

PrEP works well against HIV, but does not prevent other STIs. Not surprisingly, in the Kaiser study, rates of STIs were high and increased over time. This underscores the importance of frequent screening and treatment for STIs.

What some MSM want

Other researchers at the University of California at San Francisco (UCSF) have reviewed the Kaiser report. They noted the following:

Dedicated PrEP programs may be ideal for MSM who seek sexual health services. This is supported by interviews with MSM in San Francisco. Based on those interviews, the UCSF researchers stated that “…due to the stigma that persists regarding gay men’s sexual activities and the shame some have experienced, many participants preferred to separate sexual health care from their on-going primary care relationship.”

What do people prioritize for discussion?

According to the UCSF researchers, “People and their prospective [sexual] partners frequently exchange information about HIV test results, HIV treatment outcomes, and adherence, while discussion of other STIs is left for the morning after, or after the appearance of symptoms. Feeling safer from HIV infection while using PrEP creates space for a more robust discussion of STIs.” The UCSF researchers further stated that “PrEP is best combined with a parallel plan to prevent other STIs, which may include use of condoms, frequent testing and treatment, and discussion of STI test results with prospective partners.”

Time to start talking about other STIs

In light of the rising rates of STIs among some sexually active MSM, the UCSF researchers made the following statement:

“It is time for a vigorous conversation about sexually transmitted infections, too long eclipsed by fear of HIV infection. The conversation should include public health officers, clinicians, clients, and sexual partners.”

—Sean R. Hosein


Moving PrEP into practice: an update on research and implementationPrevention in Focus

Pre-exposure prophylaxis (PrEP) – CATIE fact sheet

“On-demand” PrEP strategy highly effective for gay men who have frequent sexCATIE News

Interim guidance on providing HIV PrEP – Quebec Ministry of Health (French only)

Clinical practice guidelines for providing PrEP – U.S. Centers for Disease Control and Prevention (CDC)

Clinical providers’ supplement for providing PrEP – CDC


  1. Mayer KH and Bryrer C. Antiretroviral chemoprophylaxis: Proud and pragmatism. Lancet. 2015; in press.
  2. Volk JE, Marcus JL, Phengrasamy T, et al. No new HIV infections with increasing use of HIV preexposure prophylaxis in a clinical practice setting. Clinical Infectious Diseases. 2015; in press.
  3. Koester KA, Grant RM. Keeping Our Eyes on the prize: No new HIV infections with increased use of HIV pre-exposure prophylaxis. Clinical Infectious Diseases. 2015; in press.

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