Overview of HIV Testing Mark Gilbert, MD Director, Applied Epidemiology Unit Ontario HIV Treatment Network October 26 2015 Harm Reduction Conference
Objectives To answer the following questions: 1. What happens in the blood after someone is exposed to and gets HIV? 2. What do HIV tests detect, and when? 3. When should someone be tested for HIV, and how often? 2
Why is HIV testing important? 25% of HIV infected persons in Canada are unaware (believed to be lower in Ontario) 3.5 times higher risk of passing on HIV if someone is unaware of their HIV status Earlier diagnosis and starting antiretroviral treatment right away has the best clinical outcome Testing is a key part of HIV prevention: If people are aware they have HIV, they change their behavior Being on treatment lowers viral load and reduces chance of transmission Diagnosis and treatment in pregnancy can prevent infection of infants Core element of Ontario s HIV/AIDS Strategy Marks JAIDS 2005; Weinhardt AJPH 1999; Brenner JID 2007; Marks AIDS 2006; PHAC 2009; Bernstein Arch Int Med 2008 3
Testing is a critical step for prevention Individual Benefit: Improved clinical outcomes Infection Diagnosis Partner notification and referral Access to HIV primary care HAART Retention in care, support Public Health Benefit: Prevention of transmission 4
When will an HIV blood test first become positive after someone is infected with HIV? 1. One week 2. Three weeks 3. One month 4. Three months 5. Six months 5
Stage of Infection Acute Infection Advanced HIV Primary Care Guidelines for the Management of HIV/AIDS in British Columbia, BCCFE, 2011 (page 13) 6
Acute HIV infection & sero-conversion symptoms Acute HIV infection happens is the first stage of infection when the virus takes hold in the body HIV virus begins multiplying in the body leading to high concentrations of the virus; individuals with Acute HIV Infection are especially infectious during this period High viral load can produce seroconversion symptoms and illness in about 50% - 90% of those infected; if symptoms do occur, it is usually 10-25 days after HIV exposure and they usually last 1-2 weeks Most common seroconversion symptoms include: flu-like symptoms, swollen glands, and a body rash, especially on the trunk of the body 7
HIV Life Cycle Antibodies P24 antigen RNA http://afa.org.sg/portfolio-item/updates-on-hiv-treatment (accessed Oct 13 2015) 8
Virus detection tests p24 antigen tests PCR tests Viral RNA (Pro-viral DNA) 9
Antibody tests Enzyme Immunoassays (EIA) Western Blot Rapid or Point of Care tests 10
Antibody and antigen 4 th generation EIA tests 11
Window periods Infection Detection Very difficult to measure (repeat blood donors) Usually based on models, averages, or estimates Not absolute: Substantial individual variation (slow and fast responders) Clinical acumen remains important 12
Why important? Accuracy (False negatives) Time to test following high risk exposure Detect acute HIV infections Brenner JID 2007; Fraser CROI 2006; Galvin Nature Rev Micro 2004; Hayes JID 2005 13
Appearance of markers of HIV infection Taylor, Int J STD AIDS, Jun 2015 14
Window periods of tests used in Ontario Blood test Taylor et al, Int J STD AIDS, June 2015. 15
Current HIV testing algorithm in Ontario Point of Care Reactive or Window Period Borderline or Reactive EIA P24 antigen & antibody Nonreactive Nonreactive Reactive Western Blot Non-reactive or indeterminate p24 Antigen Antibody Blood Test (PHO lab) Reactive Nonreactive Positive for HIV antibody Evidence of HIV infection prior to seroconversion Inconclusive HIV antibody non-reactive 16
What is the window period? 100 % EIA (Antibody only; 3 rd gen) EIA (Antibody+Antigen; 4 th gen) Percent of people who will have a reactive test result 0 % Time since HIV infection starts Adapted from Taylor et al, Int J STD AIDS, June 2015. 17
So. when do I recommend testing? 18
HIV Testing Frequency Guidelines The AIDS Bureau worked with researchers and clinicians to develop recommendations for the testing frequency of persons at high risk of HIV exposure (2012). The recommendations were developed based on HIV prevalence in populations in Ontario and the risk behaviours that increase the likelihood of exposure to HIV. The recommendations apply to: HIV Negative Gay, Bisexual and other MSM People Who Use Drugs (Injection and Non-Injection) (Men & Women) African/Caribbean/Black Ontarians (Men & Women) Indigenous Populations (Men & Women) Heterosexual men and women engaging in HIV risk activities with populations with higher HIV prevalence Reference: Ontario HIV Testing Frequency Guidelines: Guidance for Counselors and Health Professionals; AIDS Bureau, Ministry of Health and Long-term Care, April 2012 19
Testing after a possible high risk encounter 3&6, 3&6 High risk exposure 3 weeks 6 weeks 3 months 6 months (post exposure prophylaxis only) 20
If symptoms of acute HIV infection 21
Recommendations include: Testing on presentation of symptoms or if none, at 3 weeks after each high risk encounter to optimize P24 testing If multiple or ongoing high risk encounters, determine best testing frequency with the client More frequent testing within the window period, i.e. again at 6 weeks after encounter and if negative, again at 3 months Testing every 12 months for priority populations at lower risk (e.g. protected vaginal or anal intercourse) OR If counsellor deems client to be at-higher risk (e.g. uncomfortable disclosing risk, mental health issues), testing may occur every six months. 22
Take home messages: With symptoms test ASAP Without symptoms 3 weeks after exposure (high risk activity) If negative and no symptoms, consider testing at 6 weeks If negative, the final test is at the end of the window period 3 months following exposure 23
Thank you mgilbert@ohtn.on.ca 24