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CATIE News: Enhancing the potential benefit of PEP

30 June 2011 - Post-exposure prophylaxis (PEP) is the use of anti-HIV drugs for 28 days after a known or suspected exposure to HIV in order to reduce the risk of infection. PEP can be used after two types of exposures: occupational exposures (such as needlestick injuries in the workplace) and non-occupational exposures (such as consensual sex, sexual assault or sharing needles). In Canada, post-exposure prophylaxis after occupational exposures is the "standard of care" and widely used. On the other hand, post-exposure prophylaxis after non-occupational exposures (nPEP) is not widely available or accessed.

In Canada:

  • No national guidelines for nPEP exist (although some provinces have developed guidelines).
  • The use of nPEP is rarely promoted.
  • The cost of nPEP (approximately $1000) is only covered by some provincial and private insurance plans.
  • nPEP is only available in some emergency departments and urgent care clinics.

As a result, nPEP is rarely offered in Canada. In contrast, many other countries in the developed world have national nPEP programs, including France, Australia and Switzerland. The United States 2010 National HIV/AIDS Strategy also includes scaling up of access to nPEP.

Enhancing the potential benefit of nPEP

It is important to explore ways to make nPEP a more effective prevention tool. Research shows that although nPEP may reduce the risk of HIV infection from a single exposure, over time it may have little impact on whether or not someone at high risk of HIV infection becomes infected.

Providing access to nPEP offers an opportunity to provide additional prevention, care, and support services to people at high risk of infection. If high-risk individuals reduce their risk of infection after using nPEP, the impact of providing nPEP will be greater.

Researchers in San Francisco recently published a randomized study looking at whether combining nPEP with more intensive risk-reduction counselling could prevent more HIV infections than less intensive counselling. The researchers found that enhanced counselling reduced the risk of infection among high-risk individuals in the year after they completed nPEP.

Study details

Between 2001 to 2002, the study enrolled 457 people who accessed nPEP within 72 hours of having unprotected sex or other high-risk exposure to HIV. All participants received 28 days of nPEP along with adherence counselling. The nPEP treatment consisted of two anti-HIV drugs (both nucleoside analogues, commonly called nukes) which were chosen based on the source person's HIV treatment history when known.

In addition to nPEP, the study randomized the participants to receive either 2 sessions (standard) or 5 sessions (enhanced) of risk-reduction counselling. The participants were followed for a year after completing their counselling sessions and nPEP use. Participants' risk behavior and HIV status were monitored during this time.

The majority of participants were male (96%) and white (71%). Most participants were at risk of HIV infection through unprotected receptive anal sex (51%) or unprotected insertive anal sex (29%). Forty percent of participants reported that the partner was known to be HIV-positive.

At enrollment, participants were asked to report the number of times they had had unprotected sex (anal or vaginal intercourse) in the previous six months. Based on this information, the study participants were classified as being at "high risk" or "low risk" for HIV infection. "High-risk" was defined as having had unprotected sex more than four times in the past 6 months while "low-risk" was defined as having had unprotected sex 4 times or less during the last six months.


The researchers did not intend to measure how effective nPEP is at reducing the risk of HIV infection from a single exposure. Instead, they looked at whether or not enhanced counselling reduced a participant's risk of HIV infection in the year after they had completed nPEP. There were 392 participants included in the analysis at the end of the study. Of these, 305 were "low-risk" participants and 87 were "high-risk."

Enhanced risk-reduction counselling did not substantially benefit the "low-risk" participants compared to those who received standard counselling. However, "high-risk" participants who received enhanced counselling were more likely to reduce their risky behaviors and less likely to become infected with HIV in the year after completing nPEP.

Both at study entry and one year after completing nPEP, researchers asked the participants how many unprotected sex acts they had had during the previous six months. Among "high-risk" participants there was an average decrease in unprotected sex as follows:

  • Standard counselling - 7 fewer acts of unprotected sex
  • Enhanced counselling - 13.2 fewer acts of unprotected sex

The percent of "high-risk" participants who became infected with HIV within one year after receiving nPEP were as follows:

  • Standard counselling - 12.3% became infected
  • Enhanced counselling - 2.4% became infected

Therefore, additional infections were prevented among "high-risk" participants by combining nPEP with enhanced counselling.  Among "high-risk" participants, enhanced counselling reduced the absolute risk of HIV infection by 9.9% and the relative risk of HIV infection by 81%. The study did not report if this difference was statistically significant.

Targeting the provision of nPEP and counselling

This study suggests that, before nPEP is started, a risk assessment should be conducted. People who access nPEP and are at high risk of infection should be provided with enhanced counselling, to reduce their risk of HIV infection after completing nPEP. However, providing enhanced counselling to individuals at low risk of infection may not be an effective use of resources.

The authors of the study conclude that nPEP "is most likely to make a public health impact only if it is targeted, used as a tool to leverage additional interventions, and the lessons learned from this study are adopted." Hopefully this study can help guide the development of provincial or national guidelines and nPEP programs in Canada.

-James Wilton

Further reading

CATIE fact sheet on post-exposure prophylaxis

CATIE Prevention in Focus article on post-exposure prophylaxis

CATIE Programming Connection case study on the nPEP program run by Clinique l'actuel in Montreal

Health Initiative for Men (HiM) position paper on nPEP


  1. Poynten IM, Smith DE, Cooper DA et al. The public health impact of widespread availability of nonoccupational postexposure prophylaxis against HIV. HIV Medecine . 2007 Sep;8(6):374-81.
  2. Rey D, Bendiane MK, Bouhnik A et al. Physicians' and patients' adherence to antiretroviral prophylaxis after sexual exposure to HIV: results from South-Eastern France. AIDS Care . 2008 May;20(5):537-41.
  3. Tissot F, Erard V, Dang T, Cavassini M. Nonoccupational HIV post-exposure prophylaxis: a 10-year retrospective analysis. HIV Medicine . 2010 Oct 1;11(9):584-92.
  4. Poynten IM, Jin F, Mao L, Prestage GP et al. Nonoccupational postexposure prophylaxis, subsequent risk behaviour and HIV incidence in a cohort of Australian homosexual men. AIDS . 2009 Jun 1;23(9):1119-26.
  5. Roland ME, Neilands TB, Krone MR et al. A randomized noninferiority trial of standard versus enhanced risk reduction and adherence counseling for individuals receiving post-exposure prophylaxis following sexual exposures to HIV. Clincial Infectious Diseases 2011 Jul;53(1):76-83.

From Canadian AIDS Treatment Information Exchange (CATIE). For more information visit CATIE's Information Network at


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