HIV is a virus that weakens and destroys the immune system over time, leaving infected individuals vulnerable to infections and diseases that would normally pose no threat to healthy people. In its most severe stage, known as AIDS, the infection becomes life-threatening, and while medical treatment can delay its progression, there is currently no cure for HIV or AIDS.

HIV-1, the most prevalent strain of the virus, was traced back to a subspecies of chimpanzees in West Equatorial Africa and is believed to have entered the human population through hunters' contact with infected blood before spreading globally. HIV is classified into two main types (HIV-1 and HIV-2), with HIV-1 further divided into multiple groups and subtypes that vary in prevalence, transmissibility, and response to treatment, making strain identification important for effective medical care.

HIV targets and destroys T-helper (CD4) cells, which are essential for signaling antibody production and coordinating the immune response, ultimately leaving the body unable to defend against infections and diseases. The infection progresses through five stages—from an initial acute infection through an asymptomatic latency period that can last years, eventually advancing to symptomatic illness and full-blown AIDS when CD4 counts drop below 200, a process that typically takes about 10 years without antiretroviral treatment.

HIV continues to disproportionately affect certain populations in the United States, with men who have sex with men (MSM) accounting for 71% of new diagnoses in 2020, and Black/African American and Hispanic/Latino communities bearing a significantly higher burden relative to their share of the population. An estimated 1.2 million people in the U.S. are living with HIV, with about 13% unaware of their status, and while overall incidence declined 8% between 2015 and 2019, achieving viral suppression through antiretroviral therapy remains critical both for individual health and for preventing transmission.

In 2020, Washington State had an estimated 14,303 people living with HIV, with 421 new diagnoses that year, the majority being males aged 25-34, and male-to-male sexual contact serving as the predominant transmission category for both existing and newly diagnosed male cases. Significant racial disparities persist, with Black women being 23 times more likely than White women to receive an HIV diagnosis, and while 88% of those living with HIV were receiving medical care, the virus continues to disproportionately impact communities of color across the state.