Previously reported seroreversion rates as high as 94% at 12 months of age led to recommendations to use EIA testing in older infants as a way to rule-out infection in asymptomatic, non-breastfeeding infants.4, 6
Although a recent study in Malawi reported that seroreversion using standard EIA tests at 15 months of age had fallen from 99% in 1993-6 to 95% in 2000-3, the absolute percentages strongly support the use of EIA in their setting.7
However, the specificity of third-generation standard EIAs was only 22% in our cohort of HIV-uninfected Vietnamese infants at 12 months of age.
The reasons for our false non-negative rate of almost 80% are unclear. Current EIAs can reliably identify infection with a variety of HIV-1 subtypes, but a few studies have found subtype-related variations in assay performance.8, 9
Thai and US investigators using a less sensitive EIA (Vironostika-LS EIA, bioMérieux, France) to estimate the window periods of adults with recent infection, found significant differences between patients with subtype B and circulating recombinant form 1 (CRF01_AE).9
Comparing our results from Ho Chi Minh City, where the dominant subtype is CRF01_AE,10, 11
with the much higher seroreversion rates observed in previous studies from South Africa and Malawi, where subtype C predominate,4, 7
raises questions about when the EIA would be a reliable tool to rule-out infection in HIV-exposed but uninfected Vietnamese infants.
With regards to what factors might influence seroreversion on an individual level, our analysis found an association with increased height at 12 months. Height is preserved relative to weight during periods of malnutrition, and takes longer to recover.12, 13
Higher height-for-age Z scores may indicate stable growth and development over time, but the connection to HIV antibody titers is unclear. There was some question of whether maternal protease inhibitor use had an impact on delaying seroreversion, potentially through greater reductions in peripartum viral load. Moreover, mothers who received protease inhibitors were more likely to have higher CD4 counts and less advanced clinical disease. However, US and South African studies have not shown an association between maternal antibody titers and false-positive infant antibody testing.14,15
The kinetics of HIV antibody in an uninfected child are likely to be related to a combination of maternal peripartum and early infant health factors.
Recent studies have demonstrated that rapid HIV tests of serum and oral fluid have lower relative sensitivity in infants than adults, which is an advantage when used to rule-out disease.15, 16
In Uganda, the Determine HIV 1/2 rapid test (Abbott, The Netherlands) had a negative predictive value of 100% among 3–18 month olds, and a positive predictive value of 83% among 9–12 month olds.17
A study of 9-month old infants in Kenya observed specificities of 90% with the Determine and 96% with the Bioline (Standard Diagnostics, Republic of Korea) rapid test kits.18
In South Africa, the OraQuick Rapid HIV 1/2 Antibody test (Orasure Technologies, Inc., United States) had a positive predictive value of 68% using an oral fluid sample compared with 15% for a standard serum EIA test in a cohort of 11–18 month old infants.15
However, there are no published data on the use of these assays in Asian infants.
Our study was limited by not including rapid tests in our algorithm. In addition, our study population was composed of full-term infants who had stable access to nutritional supplements. Because prematurity or malnutrition can affect waning of maternal antibody, our results may not apply to preterm infants and those in more resource-limited areas. We also applied strict criteria for categorizing non-negative EIA test results. In practice, laboratories may consider samples close to the optical density threshold as indeterminate rather than positive. With regards to our analysis, we were unable to include variables related to the mother’s HIV disease (e.g., maternal viral load) to examine their potential association with prolonged time to seroreversion.
Low-cost and easily accessible diagnostic tools are needed to identify infected children for care and treatment, and provide reassurance to the families of the larger, uninfected proportion of the HIV-exposed infant population. In our setting of low rates of breastfeeding, indeterminate EIAs at these ages could be reliable evidence for waning maternal antibody and lack of infant infection. However, our results show that we may need to shift expectations of providers and policy-makers regarding HIV seroreversion by standard EIAs to reflect potential cross-regional differences in their performance.