Prevalence and incidence are measures of disease frequency that are used to inform our response to the HIV epidemic. Prevalence is the total number of people living with HIV in an area in a year, while incidence is the number of new infections that occur in an area over a year.
New HIV diagnoses (i.e., case reports) are the foundation of HIV surveillance in British Columbia. However, because they only include individuals who are tested for HIV, these data are an imperfect substitute for HIV incidence. Case surveillance for HIV is also limited in its ability to generate prevalence counts, since prevalence must account for historical data and data on migration and death. For these reasons, models are needed to incorporate various sources of knowledge about the HIV epidemic and produce estimates of HIV prevalence and incidence in the population.
The Public Health Agency of Canada (PHAC) has recently released national estimates of HIV prevalence and incidence for 2014 based on modelling and multiple data sources. Here are the 2014 PHAC estimates of HIV incidence and prevalence for the province of British Columbia.
HIV prevalence has increased over time to an estimated 12,100 (range 9,700-14,500) people living with HIV in BC at the end of 2014, compared with 11,655 (range 9,310-14,000) in 2011. This rise is explained by the accumulation of incident cases and by decreases in HIV-related deaths.
Almost half of people living with HIV at the end of 2014 are gay, bisexual, or other men who have sex with men (MSM) and over a quarter are people who reported a history of injection drug use (IDU) (Table 1).
Table 1: Estimated HIV Prevalence in British Columbia at the End of 2014
There was an estimated 305 (range 210-400) incident HIV infections in BC in 2014. Overall, the incidence of HIV has been decreasing in BC since the 1980s (Figure 1). About 60% of incident HIV infections were among MSM (Table 2).
Figure1: Estimated HIV Incidence in British Columbia, 1975-2014
Table 2: Estimated HIV Incidence in British Columbia in 2014
Comparison to surveillance data
Overall, the HIV incidence estimates from PHAC are consistent with BCCDC’s HIV surveillance data, which have similarly found a generally decreasing number of new HIV diagnoses and almost 60% of new diagnoses being among MSM.
The increasing prevalence of HIV estimated by PHAC HIV prevalence is also consistent with BC surveillance data which has found a decreasing rate of AIDS reports in BC. This suggests that there are fewer people who are diagnosed with complications of HIV and thus, fewer people are dying of HIV-related causes.
National estimates are presented in more detail in Estimates of HIV incidence, prevalence, and proportion undiagnosed in Canada, 2014 on the PHAC website.
Provincial estimates are shown in the BC Centre for Disease Control HIV Annual Report, 2014.
- Travis Salway Hottes
- Public Health Agency of Canada (PHAC)