The optimal time to test for sero-reversion in HIV-exposed uninfected infants: the later the better?

HIV-exposed uninfected (HEU) infants are tested for loss of maternal antibody (sero-reversion) at 18 months of age. Highly sensitive fourth-generation antigen/antibody assays can detect very low levels of antibody, leading to retesting. We audited serological screening outcomes in HEU infants at two National Health Service (NHS) Trusts.

HEU infants born between January 2013 and August 2016 were identified via case records. Data collected included gestation; age at testing; test results and assay type.

One hundred and forty-two infants were identified, of whom 21 were excluded from analysis. One hundred and one (83%) were born at term and 20 (17%) preterm (< 37/40 weeks of gestation), and the median age at first serology was 19.1 [interquartile range (IQR) 18.1; 21.4] months. Initial serology was positive in 10 of 121 infants (8.3%), and the median age of these 10 infants was 18.3 (IQR 18.1; 18.8) months, whereas those with negative serology (n = 111) had a median age of 19.2 (IQR 18.1; 21.5) months (P = 0.12). All infants with positive HIV serology were born at term. Seven of 10 infants had reactive serology on two fourth-generation assays. Subsequent serology was available for eight of 10 infants, with a median age of 21.3 months. Five of the eight (63%) were negative. One was reactive but HIV RNA polymerase chain reaction (PCR) was negative, and one was reactive on screening but negative on confirmatory testing. The remaining child was still seropositive at 24.7 months but had a non-reactive result at 29.4 months.

Overall, 8.3% of HEU infants required repeat testing to confirm loss of antibody. Delaying testing until 22 months of age reduces retesting to < 2%, with associated resource and emotional implications. Positive serology at 22 months should prompt an HIV RNA PCR to exclude infection.