Dr. Darrell Tan

Dr. Darrell Tan, infectious diseases physician at St. Michael’s Hospital, is the lead author on the latest national guidelines for HIV Prevention Medication. The updated guidelines, published in the Canadian Medical Association Journal offers Canadian health care providers, community members and policy-makers the latest insights on prescribing HIV medications, in an effort to ensure the life-saving drugs are equitably prescribed and bring down rising infection rates.

The guidelines come at a critical time as research shows that HIV cases are spiking in Canada. The federal government reported 2,434 people newly diagnosed with HIV in Canada in 2023, which is a 35% increase over previous years. Marginalized communities face disproportionately higher cases, calling for more guidance and equitable prevention tools.

World AIDS Day, marked each year on December 1, is an opportunity to draw attention to the AIDS epidemic, and a reminder of the impact HIV and AIDS continues to have today.

We spoke with Dr. Tan about the need for the guidelines, why they’ve been released now and what populations will be affected the most.

Let’s start with your background. Can you describe your research in general at St. Michael’s?

I’m an infectious diseases physician and clinician-scientist, and my doctoral training is in clinical epidemiology. A major goal of my work is to expand the range of tools that we have available for treating and preventing sexually transmitted and blood borne infections, notably HIV – the virus that causes AIDS. My team and I do this through a number of methods like clinical trials, but we also work in the field to learn how to implement prevention tools in the real world.

My research team is called the Options Collaboratory in HIV and STI Treatment and Prevention Science (Options Lab). We work to maximize the range of medical options available to people seeking HIV and STI treatment and prevention care, because we know it’s not a one-size-fits-all solution. We’re a team with expertise in clinical science, social science, public health science, and most importantly community engagement.

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Can you talk about the need for updated guidelines around Pre- and Postexposure Prophylaxis (PrEP and PEP) medications in Canada, and why these guidelines are released now?

There’s a story behind it, actually. The first clinical trials demonstrating that PrEP is a safe and effective strategy for preventing HIV infection were published in 2010. PrEP is a profound intervention, and was eventually approved by Health Canada in 2016. The hope was that we would see a rapid uptake in its use. But we were hearing from medical colleagues that they wanted guidelines for prescribing PrEP. In fact, some physicians would point to the absence of Canadian guidelines as the reason for not prescribing the medication. Prescribing PrEP was also controversial because of the stigma around HIV and AIDS, and the behaviours that lead to transmission, such as sexual activity and injection drug use.

Faced with this inaction, we took the initiative to put together Canada’s first and only national guidelines on PrEP and PEP, which were published in 2017, to show what is evidence-based, effective and standard practice for prescribing these medications. But even though those first guidelines got a lot of attention, and despite the fact that PrEP has now been around for over a decade, the incidence of HIV in Canada has worsened.

So, it was critically important to update the guidelines and focus on equity gaps in how PEP and PrEP are prescribed and accessed in Canada. This was a concern that came up with the original guidelines, and we’ve now emphasized that PEP and PrEP are tools that need to be equitably deployed to bring down HIV numbers in this country.

What populations will the new guidelines affect the most?

Efforts to contain epidemics benefit all of us, and the HIV numbers are too high in our country as a whole. PrEP in particular has been taken up the most among sexual minority men who have historically represented half of HIV infections in Canada since the dawn of the epidemic. But even in this group, the uptake hasn’t been equitable by race, urban and rural divide, or socio economic status.

We’re seeing HIV numbers rise among Indigenous people and cisgender women in Canada. Gender diverse and transgender people are also important populations who are often lumped together with sexual minority men, but each community has distinctive characteristics and we mustn’t conflate them. Another important group is people who inject drugs and use substances. This group has been under-represented in biomedical HIV prevention work.

Who was involved in creating the new guidelines?

We worked to include sex, ethno-racial, and geographic diversity within the panel of experts. Certainly there was disciplinary diversity, and we included community expertise as well. Many of the key populations that are disproportionately affected by HIV in Canada were represented in the panel, and people with lived experiences and professional experiences.

 We also met with regional organizations representing different communities in Canada, like women’s groups, minority groups, and Indigenous groups to share their recommendations for the updated guidelines. I believe we made meaningful changes to the content of the guideline based on this input.

What does it mean to you that the updated guidelines are released on World AIDS Day?

This day reminds the whole world how important HIV and AIDS continues to be today. Many people have the impression that HIV is a problem of the past, but it continues to be a major public health issue all over the world, including in Canada. Paradoxically, we have worsening HIV incidence in Canada even though we have so many safe and effective tools to control the epidemic, including but not limited to PrEP and PEP. It represents an urgent need to re-double our focus and efforts.

We have excellent treatments for HIV and AIDS, and we can care for our patients living with HIV very well, but it is still an incurable condition and we must prioritize prevention.

Click here to read: “Canadian Guideline on HIV Pre- and Postexposure Prophylaxis: 2025 Update” developed through the CIHR Pan-Canadian Network for HIV and STBBI Clinical Trials Research (CTN+).

By Christine Davidson

Photos by Kevin Van Paassen, Unity Health Toronto

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