I had a risky exposure on Jan. 17, 2019. I tested negative at 13 days (RNA), 18 days (RNA), 20 days (RNA), 27 days (4th gen), 34 days (4th gen), 48 days (4th gen) and 90 days (4th gen). What are the chances I could still be positive? I haven't had any risky encounters since the initial one. What would cause someone to not develop antibodies until after 90 days?
Hello and thank you for your inquiry.
You are inquiring about the reliability of seven HIV tests you received since a 'risky' exposure.
The HIV NAAT (RNA) test is a very sensitive test designed to detect HIV RNA in blood. RNA is the viral equivalent to human DNA. The NAAT test is able to detect HIV RNA as early as seven to 14 days after infection with HIV.(1) Your most recent RNA test performed at 27 days can be considered conclusive.
Fourth-generation HIV tests can detect HIV infection in 50% of people by 18 days after infection; 95% of people by 34 days after infection; and 99% of people by one and a half months after infection. These tests have a sensitivity of about 99.9%. (2) You can consider your most recent 4th generation HIV test performed at 90 days post exposure to be conclusive.
There are 2 rare exceptions which may require someone to retest up to six months after exposure:
People who have a severely impaired immune system may take longer to develop HIV antibodies.(1)
People who have taken post-exposure prophylaxis (PEP). This is a one-month course of anti-HIV drugs that, if started within 72 hours of potential exposure, may reduce the risk of HIV infection. If PEP does not successfully prevent HIV infection in someone, the presence of the PEP drugs may still reduce HIV replication until the drugs are finished. This may delay the time it takes for a person’s body to create HIV antibodies.(1) If you have taken PEP, the normal window period for any given test begins when you finish the course of PEP treatment, rather than on the initial exposure date.
Given that you have not had an exposure since the initial one, and have tested negative several times outside the window periods with very effective testing methods, you can confidently consider yourself to be HIV negative.
Recommendation: No further testing required for this exposure.