This sub-study included 2,561 women enrolled in the PEPI-Malawi trial. There was no significant difference in the frequency of in utero
HIV transmission among the 2,561 women included in the study and the 774 women who were not included in the study (7.0% vs. 6.2%, respectively, P=0.48, Fisher’s exact test). Fifty-four of the 2,561 women included in the study were previously diagnosed with HIV infection in the Nevirapine and Zidovudine (NVAZ) trial, which was conducted in 2000–2004 at the same study sites as the PEPI-Malawi trial [32
]. Therefore, those 54 women were known not to have recent HIV infection when they subsequently enrolled in the PEPI-Malawi trial. The median duration of time between their enrollment in the NVAZ trial and their subsequent enrollment in the PEPI-Malawi trial was 4.3 years (range: 2.3–6.1 years). Overall, 179 (7.0%) of the 2,561 women had infants who were diagnosed with HIV infection at the time of birth (in utero
Maternal samples collected at delivery from the 2,561 women were analyzed using the BED and avidity assays. Results from those assays were combined with results from CD4 cell count and HIV viral load testing to identify women with recent HIV infection (). The performance of the MAA in individuals likely to be infected with subtype C HIV was evaluated by analyzing samples from individuals from subtype C endemic areas who had known duration of infection (see Methods). In those individuals, the positive predictive value of the MAA for identifying individuals with recent HIV infection (defined as <180 days) was 93.9%; that result can be compared to the result obtained by testing the same sample set with the avidity assay alone using a standard assay cut-off of 40% (positive predictive value: 90.9%), and to the result obtained by testing the same sample set with the BED assay alone using a standard assay cut-off of 0.8 OD-n (positive predictive value: 71.7%).
Using the MAA described above, 73 (2.9%) of the 2,561 women were identified as recently infected; the remaining 2,488 women were identified as not recently infected. All but nine of the 2,488 women were identified as not recently infected based on results of serologic testing (BED>1.0 OD-n and/or avidity >80%, ). Those nine women had low BED and/or low avidity test results. Four of those nine women had CD4 cell counts <200 cells/ul and five of those women had viral loads <400 c/ml (). Individuals who have low CD4 cell counts and low HIV viral loads are unlikely to be recently infected; furthermore, those factors have been associated with misclassification of individuals with non-recent HIV infection as recently infected using serologic HIV incidence assays [20
None of the 54 women who had known non-recent HIV infection when they enrolled in the PEPI-Malawi trial were misclassified as recently infected using the MAA (0/54 vs. 73/2507, P=0.40, Fishers exact test). In addition, nine women (0.4% of the 2,561 women included in this study) were receiving antiretroviral therapy at the time of enrollment into the PEPI-Malawi trial (a co-formulated regimen of stavudine, lamivudine and nevirapine; Triommune, Cipla, India); none of those women were identified as recently infected using the MAA and none had an infant who was HIV-infected in utero. The median time between antiretroviral treatment initiation and enrollment in the PEPI-Malawi trial for those nine women was 56 days (range: 3–263, interquartile range: 25–97 days). They had a median CD4 cell count of 180 (range: 33–701 cells/mm3, five had a CD4 cell count <200 cells/mm3) and a median log10 HIV viral load of 2.73 (range: 2.30–4.36 copies/ml) at enrollment.
shows demographic, clinical, and laboratory characteristics of the 73 women who were identified as recently infected using the MAA and the 2,488 women identified as not recently infected by the MAA. Women who were identified as recently infected using the MAA were younger and had lower parity than the women who were identified as not recently infected (median age: 23 vs. 26 years, P<0.0001, Wilcoxon test; median parity: two vs. three pregnancies, P<0.0001, Wilcoxon test). Women identified as recently infected by the MAA also had significantly higher CD4 cell counts at delivery; this is partly explained by the fact that the MAA excludes women with CD4 cell counts below 200 cells/mm3 from the recently infected group. There was a significant association between recent maternal HIV infection (defined using the MAA) and in utero HIV transmission. The frequency of in utero HIV transmission was 17.8% in the recently infected group, compared to only 6.7% in the not recently infected group (13/73 vs. 166/2488, P=0.001, ). There was no significant association between identification of women as recently infected using the MAA and other demographic, clinical, and laboratory variables ().
Characteristics of women identified as recently infected and as not recently infected using a multi-assay algorithm (PEPI-Malawi trial, Malawi, 2004–2009)*.
We considered the possibility that some women who were identified as not recently infected based on CD4 cell count or HIV viral load data alone might have been misclassified; among the 2,488 women identified as not recently infected, only nine had a BED result <1.0 OD-n and an avidity result <80% (four with a CD4 cell count <200 cells/ul and five with a viral load <400 copies/ml). Even if all nine of those women were included in the recently infected group, recent infection would still have been significantly associated with an increased risk of in utero HIV infection (P=0.0062).
Logistic regression analysis was performed to assess the association between in utero HIV infection and identification of women as recently infected using the MAA, controlling for other factors (). In a multivariate model (which excluded parity because it was correlated with age), increased risk of in utero transmission was significantly associated with recent HIV infection (as defined by the MAA, adjusted odds ratio [AOR]: 2.49, 95% CI: 1.30–4.78, P=0.006), HIV viral load at delivery (per log10 increase, AOR: 2.01, 95% CI: 1.60–2.51, P<0.0001), and younger age (per 10 year increase, AOR: 0.66, 95% CI: 0.43–0.93, P=0.02), but not with CD4 cell count at delivery, or other factors ().
Association of clinical and laboratory factors with in utero HIV transmission (PEPI-Malawi trial, Malawi, 2004–2009)*