Interpretation of indeterminate HIV-1 PCR results are influenced by changing vertical transmission prevention regimens.

Background: Suppression of HIV by antiretroviral drugs may be one of the reasons that indeterminate HIV-1 PCR results are obtained from testing HIV-exposed infants. This complicates the early identification of infected infants, potentially delaying initiating treatment early. There is uncertainty as to how different vertical HIV transmission prevention regimens (VTP) affect the rate and predictive value of indeterminate PCR results.

Objectives: To investigate rates of indeterminate PCR results, outcomes of subsequent samples and the predictive value of an indeterminate PCR for a later positive result in the setting of intensifying VTP in the Western Cape province of South Africa.

Study Design: Retrospective laboratory data analysis. Diagnostic PCR data of a public health laboratory from June 2009 to October 2014 was analysed and categorised by South African VTP regimens. First indeterminate HIV-1 PCRs in patients younger than 12 months were linked with follow-up HIV-1 PCRs and/or serological tests. Linked results sets were analysed by PCR amplification characteristics and subsequent patient outcome.

Results: Over intensified VTP regimens, the rate of indeterminate and positive PCRs decreased significantly (5.6-3.2% and 2.4-0.4%, respectively; both p<0.001). Most notably, significantly more patients with indeterminate results had positive PCRs on subsequent samples during WHO Option B+ use compared to older regimens (64.1% vs. 14.7%, p<0.001) at a median 28days later.

Conclusions: Indeterminate HIV PCRs, although decreasing in frequency with Option B+, should be regarded with a high index of suspicion for being representative of true HIV-1 infections. Additional virological testing is required to arrive at a definitive diagnosis.