Sixty-nine infants born to women who initiated HAART before delivery were included in analyses; of these, 34 infants were assigned to breastfeed and 35 infants to formula feed (). The comparison group consisted of 109 infants born to women with enrollment CD4+ cell counts less than 200 cells/mm3 and naïve to HAART through 6 months postpartum; 50 of these infants were assigned to breastfeed and 59 infants to formula feed. Most factors, including the median maternal baseline CD4+ cell counts and HIV-1 RNA levels, were similar between the HAART-exposed and -unexposed groups (). The median gestational period at birth, however, was lower in the HAART-unexposed group compared with the HAART-exposed group.
Study population selection scheme according to HAART status and assigned feeding strategy.
Baseline Characteristics of Mothers and Infants in Study Population by Maternal HAART Status.
Two (2.9%) infants in the HAART-exposed group and 21 (19.3%) infants from the HAART-unexposed group were infected with HIV-1 by 7 months of age. The mother-to-child transmission rate of HIV-1 was lower in the HAART-exposed group than the HAART-unexposed group at all of the specified time points (birth, at 1 month, between 2 and 7 months, and cumulatively by 7 months). The difference was statistically significant only between 2 and 7 months and cumulatively by 7 months (p=0.04 and 0.001, respectively). Six (8.7%) infants (1 infected with HIV-1) from the HAART-exposed and 11 (10.1%) infants (4 infected with HIV-1) from the HAART-unexposed group died before 7 months of age.
Infant hematologic abnormalities by maternal HAART exposure status and assigned feeding strategy are summarized in . Proportions with grade 3 or higher hematologic abnormalities were compared between infants exposed and unexposed to maternal HAART. No difference in hematologic abnormalities was observed at birth. However, a significantly higher proportion of infants in the HAART-exposed group experienced neutropenia than those in the HAART-unexposed group at 1 month of age (15.9% vs 3.7%, respectively; p=0.006), and this significance persisted when cumulative hematologic toxicities from birth to 1 month of age were compared (p=0.002). There were no significant differences in the proportions experiencing grade 3 or 4 anemia or thrombocytopenia by HAART exposure status, and no infant experienced more than one type of hematologic toxicity at a time.
Infant Grade 3 or 4 Hematologic Abnormalities by Maternal HAART Exposure Status and Assigned Infant Feeding Strategy.
Since the breast-fed infants in the HAART-exposed group were exposed to additional ARVs through breast milk, the two groups were further stratified according to assigned feeding strategy (). Among breastfed infants, those in the HAART-exposed group—who had been exposed to maternal HAART through breastfeeding as well as in utero—experienced significantly more neutropenia than the HAART-unexposed, breastfed children at 1 month (23.5% vs.6.0% respectively; p=0.044) as well as cumulatively through 1 month (29.4% vs.8.0%, respectively; p=0.012). Among formula-fed infants only, there was no significant difference in proportions experiencing neutropenia between infants in HAART-exposed and -unexposed groups. Within the subgroup of 94 babies assigned to formula feeding, assuming a 1% rate of toxicity within the non-HAART group (n=59), this study’s sample size had 79% power to detect (by Fisher’s exact test) a 15-percentage point increase in the HAART group (n=35) (i.e., 16% rate of toxicity). Therefore, due to the study’s small sample size, there was not high power to detect smaller differences as statistically significant. Other than neutropenia, no other significant differences in hematologic enzyme abnormalities were noted between HAART-exposed and HAART-unexposed infants within each of the breast-fed and formula-fed strata.
From 2 to 7 months of age, the cumulative hematologic toxicities from 2 to 7 months of age were not significantly associated with exposure to maternal HAART among breastfed infants. No hematologic toxicities were observed in formula-fed infants during the same period (as noted in the Methods section, CBC was performed 6 times in breastfed infants compared to twice in formula-fed infants, and thus direct comparison between the two feeding groups is not advisable).
Despite the association between infant neutropenia and maternal HAART exposure during the first month of life, median infant ANC values and maternal HAART exposure were not significantly associated during the same period (). The median ANC levels in the HAART-exposed and –unexposed groups were 6300 and 7300 counts at birth (p=0.43) and 1700 and 1900 counts at 1 month of age (p=0.14), respectively. Breastfed infants had lower ANC levels than formula-fed infants in both HAART-exposed and HAART-unexposed groups. This result is expected as breastfed infants received a 6-month prophylactic zidovudine therapy compared to 1-month regimen for formula-fed infants, and neutropenia is a well-known adverse effect of zidovudine.
Figure 2 Progression of absolute neutrophil counts overtime in infants (A&B) and cumulative proportion of infants having experienced a grade 3 or 4 neutropenia (C&D) stratified by maternal HAART exposure (A&C) or by maternal HAART exposure (more ...)
Association between maternal HAART exposure and neutropenia was further analyzed using time-to-event methods. HAART exposure, assignment to breast feed, and higher maternal viral load at enrollment were each statistically significantly associated with neutropenia. Controlling for maternal HIV-1 viral load and feeding assignment (which also controls for the different schedule of CBC between the breastfed and formula-fed infants), exposure to maternal HAART had a hazard ratio of 3.1 for neutropenia compared to those without HAART exposure (95% CI; 1.4 to 6.9).
The cumulative proportion of infants experiencing neutropenia is shown in . Through 7 months of age, a significantly higher proportion of HAART-exposed infants have experienced neutropenia compared to HAART-unexposed infants (p=0.007). When stratified by assigned feeding strategy, the same pattern was observed (p=0.042 among breastfed infants, and p=0.064 among formula-fed infants). In accordance with the results shown in , the difference in the proportions of infants experiencing neutropenia was concentrated mostly between birth and 1 month of age and did not seem to persist thereafter.
All grade 3 or 4 neutropenias were resolved within a month; no infant experienced neutropenia in two consecutive months. Out of 21 infants who experienced neutropenia by 1 month of age, 3 infants (1 at birth and 2 at 1 month of age) experienced a grade 4 neutropenia. All 3 infants had not been exposed to maternal HAART. In addition, clinically significant toxicities were rare in our study. Out of 37 infants in this nested cohort study who experienced one or more hematologic toxicity, only one infant exhibited clinical symptoms consistent with severe anemia in the breastfed HAART-exposed group. All neutropenic and thrombocytopenic infants as well as two infants with hepatic toxicities were clinically asymptomatic.
Proportions of infants with grade 3 or higher hepatic enzyme abnormalities were compared between infants exposed and unexposed to maternal HAART. No statistically significant difference in hepatic enzyme abnormalities was observed between the groups at 1 month of age. One (1.4%) infant exposed to maternal HAART had an abnormal ALT level whereas no infant in the HAART-unexposed group experienced an ALT abnormality (p=0.39). Two (2.9%) infants in the HAART-exposed group and no infant in the HAART-unexposed group experienced AST abnormality (p=0.15). Of the two infants experiencing hepatic toxicities, one had both ALT and AST levels of grade 4, and the other had a grade 3 AST level. Both infants were infected with HIV, formula-fed, exposed to maternal HAART in utero, and had not initiated infant HAART at the time of sample draw. At 6 months, no infant in the study experienced a hepatic enzyme abnormality.
Statistical significance in the above analyses did not change when HIV-infected infants were excluded; therefore, all infants were included in the analyses.