If you blinked, you may have missed some of the ways HIV has changed.

The science of HIV is constantly evolving, and what we knew (or thought we knew) just a few years ago is either incorrect, incomplete or in need of an upgrade. Every year we learn more about the virus, and research keeps giving us new tools to prevent, test and treat it.

1. PrEP works in the real world

Pre-exposure prophylaxis, or PrEP, is the daily use of anti-HIV medication by HIV-negative people to prevent infection before an exposure. While this latest prevention tool has been met with caution and some skepticism, recent studies have demonstrated its efficacy if taken regularly and have eased fears that HIV-negative people might abandon other prevention strategies such as condoms.

2. HIV can be detected within weeks

How long after a potential HIV exposure should you wait before getting tested? While technologies vary in every jurisdiction, the vast majority of HIV infections can be detected much earlier than in the past. Why is this important to know? Early detection can lead to better health outcomes and near-normal lifespans. It also prevents further transmission, since a large proportion of new HIV infections may come from individuals who have been newly infected.

3. Late testing can be lethal

Since the introduction of effective antiretroviral therapy in the mid-1990s, people with HIV in high-income countries can now live longer and healthier lives. However, the death rate among HIV-positive people is still higher than among HIV-negative people, and most HIV-related deaths are a result of late detection. According to a study in England, 80% of people with HIV who died had only been diagnosed after developing serious immune deficiency.

4. Undetectable viral load can be an effective HIV prevention strategy

An undetectable viral load can significantly reduce the transmission of HIV among heterosexual couples and men who have sex with men. Over the past several years, studies and expert consensus statements have confirmed this, offering an additional strategy for people living with HIV to reduce the risk of transmission.

5. Repeated exposures increase the risk of an activity

One of the most common questions faced by HIV educators is the level of risk for a specific sexual activity. Not satisfied with a broad categorization such as ‘low-riskʼ or ‘high-risk,ʼ many want to ‘put a number on itʼ so they can know the statistical likelihood of transmission for each act. What these statistics fail to capture, however, is that risk accumulates as the number of exposures increases. This means that for a low-risk activity, the risk of infection can increase the more often it happens.

6. Not every HIV exposure leads to an infection

Although the most effective way to prevent the sexual transmission of HIV is to avoid exposure to fluids that contain the virus, the reality is that not all exposures result in infection. After an exposure, HIV still needs to complete a difficult journey before it can spread throughout the body. In some cases, HIV is not able to complete this journey and infection does not occur. The likelihood of infection depends on many factors.

7. Rectal fluid can transmit HIV

Weʼve known for a long time that, in the absence of the consistent and correct use of highly effective prevention strategies (e.g. condom use, undetectable viral load, PrEP), anal sex can be a high-risk activity for the transmission of HIV. For an insertive (‘topʼ) HIV-negative partner, we used to think that the risk of infection was due to HIV being transmitted from blood in the rectum to the penis. We now know that HIV can also be present in rectal fluid, and sometimes at levels higher than those found in blood. This means that the risk of infection from insertive anal sex can be high even when there is no bleeding or tearing.

8. People arenʼt using condoms correctly

Condoms are an effective strategy for HIV prevention, but theyʼre only effective when theyʼre used consistently and correctly. A recent literature review has revealed that the incorrect use of condoms is surprisingly common, with problems including breakage, slippage, leakage and delayed application. Research shows that education and experience can help lower rates of condom failure, so get practising!

9. People with HIV can have a near-normal life expectancy

When diagnosed early and linked to treatment and care, a young Canadian living with HIV can now expect to live to their early 70s. A recent study found that overall the life expectancy for HIV-positive people has increased over the past decade and is approaching that of HIV-negative people in similar circumstances. Continued engagement in care is crucial for maximum life expectancy.

10. Prepare for an aging HIV epidemic

As people continue to live longer with HIV, the demographics of the HIV- positive population are shifting. Once an infection primarily affecting young gay men in Canada, the proportion of HIV-positive people over the age of 50 has steadily increased in high-income countries. Combined with new HIV infections occurring at an older age, healthcare providers should expect to see an increased need for services from HIV-positive seniors in the coming years.