People living with HIV can potentially transmit HIV to others through unprotected sex at any time during their life. However, emerging research suggests that a disproportionate number of HIV transmissions -- perhaps more than half -- may originate from people during the first few months after they become infected with HIV.1,2 In this article, we explore why recently infected individuals are more likely to transmit HIV to others and how we can help prevent these transmissions from occurring.
To understand why recently infected people are more likely to transmit HIV to others, we need to look at what's going on in the body after HIV infection occurs.
After someone becomes infected with HIV, the virus begins to replicate very quickly and the amount of virus in the body and bodily fluids (such as the blood, semen, vaginal fluid and rectal fluid) rises rapidly. In some individuals, this takes its toll on the body and can cause fever, fatigue, night sweats, headache, diarrhea, sore throat and/or a rash. These symptoms generally appear about two weeks after infection occurs.3 Other individuals who become infected notice no symptoms at all during this period.
A few weeks after infection, the body's immune system begins to fight back against the virus. An important part of this immune response includes the production of anti-HIV antibodies -- small proteins made by certain immune cells, which can destroy HIV and prevent HIV from multiplying. Once antibodies to HIV have been produced, HIV replication begins to slow down and the amount of virus in the body (also known as the viral load) gradually decreases. Unfortunately, antibodies cannot fully control HIV infection.
Antibodies are not produced immediately after infection. The amount of time it takes for the body's immune system to produce them varies from person to person. In most people, it is possible to detect HIV antibodies in their blood within approximately 34 days of infection, although this can take up to three months in some individuals.4 The presence of antibodies in the blood marks the end of the first stage of HIV infection -- known as acute HIV infection -- and the beginning of the next stage, chronic HIV infection.
The amount of virus in the bodily fluids is highest during the acute HIV infection stage. After antibodies are produced, the viral load slowly decreases but does not stabilize at a lower level until up to six months after infection.5-10
The elevated viral load of someone recently infected with HIV is the main biological reason that they are more likely to transmit HIV to others at this time. The higher the viral load, the greater the risk is of transmitting HIV to others through unprotected sex. Researchers estimate that the risk of transmitting HIV to another person from one act of unprotected sex is 26 times higher during the first three months after infection than during the months and years that follow.11
A high viral load alone is not enough to transmit HIV to another person; a recently infected individual also needs to be engaging in activities that can lead to the transmission of HIV, such as unprotected sex. Unfortunately, a person who has recently been infected with HIV is more likely to be engaging in high-risk behaviours than a person who has been infected for a longer period of time.12-15 There are two possible explanations for this. First, a recently infected individual is more likely to be engaging in high-risk behaviours because this is what led to their HIV infection. Second, many recently infected individuals are unaware of their HIV status and therefore may not realize the importance of having safer sex.
Because recently infected individuals account for a large number of HIV transmissions, identifying these individuals and helping them reduce their risk of passing HIV to others is critical to HIV prevention. Research shows that when people become aware of their HIV infection and are provided with access to prevention and care services, most take measures to reduce their risk of transmitting HIV to others.12
There are two major challenges to identifying recently infected individuals:
As a consequence, many people who have recently become infected are unaware of their infection, as are their partners. Those who are recently infected may therefore continue to engage in high-risk behaviours until they are diagnosed with HIV.
Your organization may be able to play a role in overcoming these challenges, identifying these individuals, and reducing their risk of transmitting HIV to others.
It is estimated that 26% of people who are HIV-positive in Canada do not know that they are infected16 and many do not learn of their HIV status until they have been infected for several years.17,18 The low levels of HIV testing in Canada means that most recently infected people probably pass through the brief stage of HIV infection when their viral load is elevated without getting tested for HIV.
People who have recently become infected may be unlikely to get tested for several reasons. Firstly, many may believe that they are not at risk for HIV infection despite participating in behaviours that put them at risk. Secondly, there are no definitive signs that someone has become infected with HIV. Only some people who have recently become infected will experience symptoms and those symptoms are not specific to HIV infection. Therefore, many people who experience symptoms may confuse them with those of another illness and not get tested. Furthermore, for people who do believe that they are at risk of infection, there are several barriers that may prevent them from getting an HIV test, including stigma and discrimination, fear of criminalization, and barriers to accessing testing and other health services.
The limitations of tests used to detect HIV infection is another major barrier to identifying recently infected individuals.
Several types of HIV tests are available but for each type of test there is a brief period of time after infection during which they are unable to detect infection in a person who is HIV-positive. The time period from when a person becomes infected with HIV to when an HIV test can detect their infection, is known as the "window period." During the "window period," an HIV test may find a recently infected person to be HIV-negative. The length of the "window period" is different for each type of test and varies from person to person.19
The HIV tests most commonly used in Canada look for antibodies to HIV in the blood. These tests cannot detect HIV infection in someone who has acute HIV infection because the body has not yet produced antibodies. The "window period" for antibody tests varies because some people produce antibodies faster than others. For most people (up to 95%), the window period of the antibody test is approximately one month, but for some individuals it may be as long as three months.
This means that for people at high risk of HIV, testing can be done as early as one month after exposure using standard antibody assays and rapid point-of-care tests. People who test positive will know for certain they are HIV-positive. Of those who test negative, 95% are indeed negative. Up to 5% of people who test negative at one month could later test positive at three months. It is important to ensure that people who test negative at one month are advised to return for repeat testing once the three-month window period is over.
Other HIV tests have been developed, which detect the virus itself -- such as the HIV RNA or the p24 antigen tests. These have shorter window periods (from seven to 14 days) than antibody tests and so can potentially detect HIV infection during the acute phase.20 Unfortunately, access to these new testing technologies varies across Canada.
Another limitation of HIV tests is the time it takes for many of them to produce results. Most HIV tests do not produce results immediately and require people to wait one to two weeks before getting the results. During this time, people may continue to engage in high-risk behaviours and some people may never return to get their test results.
Tests known as rapid or point-of-care (POC) tests can provide results on the same day that a test is performed. Most rapid/POC tests can provide results within minutes. This ensures that a person receives their results. Rapid tests that detect antibodies are available in some parts of Canada but rapid tests that can detect HIV RNA or the p24 antigen do not yet exist.
The goal of HIV prevention is to reduce the number of HIV infections in the communities we serve. A large number of HIV transmissions in your communities may be occurring from recently infected individuals, and therefore represent an important priority for HIV prevention efforts. Although several challenges exist in identifying these individuals and engaging them in prevention services, frontline organizations can play a key role in overcoming these challenges and reducing HIV transmissions.
Hottest at the Start -- A campaign by the Health initiative for Men (HiM) in BC to raise awareness on acute infection and transmission and to encourage gay men who have had a recent potential exposure to HIV to get an "early" HIV test.
James Wilton is the Project Coordinator of the Biomedical Science of HIV Prevention Project at CATIE. James has an undergraduate degree in Microbiology and Immunology from the University of British Columbia.