Lab Matters Fall 2019 | Page 32

INFECTIOUS DISEASES Preparing Public Health Laboratories for HIV Testing in a PrEP Era by Monica Parker, PhD, director, Bloodborne Viruses Laboratory, Wadsworth Center, New York State Department of Health and Anne Gaynor, PhD, manager, HIV, Hepatitis, STD & TB Programs In 2019, the US Department of Health and Human Services launched an initiative entitled “Ending the HIV Epidemic: A Plan for America” which aims to end the HIV epidemic in the United States within 10 years by implementing coordinated actions in four key areas: prevention, diagnosis, treatment and care. A central component of HIV prevention strategy involves increasing access to and use of pre-exposure prophylaxis (PrEP). PrEP consists of two antiretrovirals (ARVs), tenofovir and emtricitabine, combined into a single pill which is taken daily to prevent HIV infection. Several clinical trials have shown that PrEP significantly reduces the risk of acquiring HIV infection 1-3 and is recommended for high risk, HIV-negative adults. 4,5 A Step Forward in HIV Prevention Increasing the use of PrEP is expected to enhance HIV prevention efforts, but may also pose new challenges for laboratories when interpreting HIV diagnostic test results. HIV testing must be conducted prior to initiating PrEP to document HIV-negative status and is recommended every three months during PrEP. 4,5 A person could be incorrectly considered eligible for PrEP if they became infected concurrent with their initial diagnostic evaluation, or if they were infected prior to the evaluation but were tested within the initial test window period. 6,7 HIV infection during PrEP is extremely rare if ARVs are taken consistently as prescribed, but the risk of infection increases as adherence decreases. 6,8,9 Therefore, people can become infected after they begin PrEP, especially if they are not taking ARVs as prescribed. If someone is HIV-infected and takes or continues to take PrEP, it may affect the typical progression of biological markers of infection and lead to atypical results from serologic and nucleic acid tests used to monitor HIV status during PrEP. 30 LAB MATTERS Fall 2019 We have learned from studies in which ARV treatment was initiated during acute HIV-1 infection before antibodies developed that seroconversion may be delayed or not occur at all. 6,7 The most profound effects on antibody development were seen when ARV treatment was initiated in patients at the earliest stage of acute infection before p24 antigen could be detected. 6 Delayed seroconversion has also been shown to occur when PrEP is continued after HIV-1 infection takes place 11 because the two-drug combination used for PrEP—while not as potent as the regimens used to treat HIV-1 infection— can substantially reduce HIV-1 replication. Preparing for the Unusual Laboratories that conduct HIV testing on specimens collected from individuals on PrEP may encounter unusual or inconsistent test results. Serological screening tests, including HIV antigen/ antibody (Ag/Ab) immunoassays, may produce a low or borderline signal (just above or just below the cut-off). In some cases, successive specimens taken on different days may fluctuate between a reactive and non-reactive result. HIV-1 RNA tests may also show weak reactivity and, in some cases, viral RNA may be suppressed below the detection level leading to a false negative result. Importantly, the APHL recommended reporting language for HIV diagnostic testing 10 may not be appropriate for interpreting results from people on ARVs. Since the number of people on PrEP is likely to increase under the new initiative, there are some actions that public health laboratories should consider. It may be helpful to include a disclaimer on all negative or inconclusive test reports, stating “Antiretroviral drugs taken for treatment or prophylaxis may limit the ability of diagnostic tests to detect HIV infection.” Laboratories may also consider adding a question to the test requisition PublicHealthLabs @APHL