- U.S. study finds that HIV is most likely to be transmitted when a person is undiagnosed
- 80% of transmissions originate in those who are undiagnosed or not receiving HIV care
- The research highlights the need for testing and linkage to treatment and care
In the United States (US) in 2015, among the 1.1 million people with an HIV infection, 15% were undiagnosed, 37% were not in care and 49% were not virally suppressed. These rates are comparable to 2018 estimates from Canada, with 14% undiagnosed, 30% not in care and 37% not virally suppressed among an estimated 63,110 people with HIV.1
Early diagnosis of HIV and engagement in care and treatment is important for both the health of the person with HIV and for the prevention benefits. People who maintain an undetectable viral load can live long and healthy lives and do not transmit HIV to their sexual partners.
A recent study from the US considered HIV transmission rates along the continuum of care.2 Rates decreased across the continuum, with the highest transmission rates occurring in people who were unaware of their HIV status.
Researchers used a modeling approach to estimate 2016 HIV transmission rates along the continuum of care using national surveillance data.
The model included 23,000 people representing the 1.1 million people with HIV in the US.
The following population groups were included in the study:
- men who have sex with men (MSM)
- people who inject drugs
- men who have sex with men who inject drugs
- heterosexual men and women
The estimated HIV transmission rate was 3.5 new HIV infections per 100 person-years in 2016, which was a decline from the 2010 rate of 4.5 per 100 person-years. This corresponded with an increase in viral suppression among people with HIV over those years.
In the model, approximately 80% of HIV transmissions were from people who have an undiagnosed HIV infection or are not receiving care:
- 4% of new HIV infections from people with acute HIV infection but unaware of their status
- 34% of new HIV infections from people non-acutely infected and unaware of their infection
- 43% of new HIV infections from people who are aware of their HIV infection but are not in care
The remaining 20% of HIV transmissions were from people who are receiving care but not virally suppressed:
- 20% of new HIV infections from people receiving HIV care but not virally suppressed
- 0% of HIV transmissions from people taking antiretrovirals and virally suppressed
The 2016 model found that the rates of new HIV infections (per 100 person-years) decreased along the HIV continuum of care as follows:
- 16.1 per 100 person-years in those acutely infected and unaware of their infection
- 8.4 per 100 person-years in those non-acutely infected and unaware of their infection
- 6.6 per 100 person-years in those aware of their HIV infection but not in care
- 6.1 per 100 person-years in those receiving HIV care but not virally suppressed
- 0 per 100 person-years in those taking antiretrovirals and virally suppressed
The percentages of new HIV transmissions from each of the populations were as follows:
- 73% from MSM
- 10% from people who inject drugs
- 5% from MSM who inject drugs
- 12% from heterosexuals
The highest transmission rates were among those aged 13–24 years (5.1 per 100 person-years), although the highest percentage of transmissions (29%) was in people aged 55 years and over because of the size of this population.
Implications for service providers
HIV transmission needs to be addressed across the continuum of care, starting with testing. A variety of testing efforts need to be implemented with the aim of reaching the undiagnosed and identifying all people with HIV soon after infection. Once an individual is diagnosed, rapid linkage to and retention in care is important to attain and maintain an undetectable viral load. Barriers to care and adherence need to be addressed to ensure people can remain engaged in care and maintain a suppressed viral load over time. Finally, increasing public awareness of viral suppression could also lessen stigma and improve health outcomes.
- Public Health Agency of Canada. Summary: Estimates of HIV Incidence, Prevalence and Canada’s Progress on Meeting the 90-90-90 HIV targets, 2016. Ottawa: Public Health Agency of Canada; 2019. Available from: https://www.canada.ca/en/public-health/services/publications/diseases-conditions/summary-estimates-hiv-incidence-prevalence-canadas-progress-90-90-90.html
- Li Z, Purcell DW, Sanson SL et al. Vital signs: HIV transmissions along the continuum of care – United States, 2016. Morbidity and Mortality Weekly Report. 2019; 68(11):267-72.