10 • JID 2007:196 (1 July) • BRIEF REPORT
B R I E F R E P O R T
Late Postnatal Transmission of HIV-1
and Associated Factors
Taha E. Taha,1Donald R. Hoover,4Newton I. Kumwenda,1
Susan A. Fiscus,5George Kafulafula,6Chiwawa Nkhoma,7Shu Chen,1
Estelle Piwowar,2Robin L. Broadhead,6J. Brooks Jackson,2
and Paolo G. Miotti3
1Department of Epidemiology, Bloomberg School of Public Health,
Care Policy and Aging Research, Rutgers University, Piscataway, New Jersey;
5Department of Microbiology and Immunology, University of North Carolina,
College of Medicine, University of Malawi, and
College of Medicine–Ministry of Health Research Project, Blantyre, Malawi
2Department of Pathology, School of Medicine, Johns Hopkins University,
3Office of AIDS Research, National Institutes of Health,
4Department of Statistics and Institute for Health, Health
6Departments of Obstetrics and Gynecology and of Pediatrics,
7Johns Hopkins University–
(See the editorial commentary by John-Stewart, on pages 1–3.)
mine the risk and timing of late postnatal transmission (LPT)
of human immunodeficiency virus type 1 (HIV-1).
Breast-fed infants previously enrolled in 2 trials
of antiretroviral prophylaxis were monitored in Malawi. Kap-
lan-Meier and proportional hazard models assessed cumulative
incidence and association of factors with LPT.
Overall, 98 infants were HIV infected, and 1158
were uninfected. The cumulative risk of LPT at age 24 months
was 9.68% (95% confidence interval, 7.80%–11.56%). The in-
terval hazards at 1.5–6, 6–12, 12–18, and 18–24 months were
1.22%, 4.05%, 3.48%, and 1.27%, respectively.
The risk of LPT beyond 6 months is sub-
stantial. Weaning at 6 months could prevent 185% of LPT.
The present study was undertaken to deter-
In Africa, HIV-infected women continue breast-feeding their
postexposure prophylaxis with nevirapine (NVP) and zido-
Received 9 October 2006; accepted 23 January 2007; electronically published 24 May 2007.
Potential conflicts of interest: none reported.
Presented in part: XVI International AIDS Conference, 15 August 2006, Toronto, Canada
Financial support: Fogarty International Center, National Institutes of Health (AIDS FIRCA
award 5R03TW01199 and supplement); Doris Duke Charitable Foundation; Gustav Martin
Innovative Research Fund of the Johns Hopkins Bloomberg School of Public Health;
discretionary fund of the HIV Prevention Trials Network, Division of AIDS, National Institutes
of Health (grant U01 A148005).
Reprints or correspondence: Dr. Taha E. Taha, Rm. E7138, Dept. of Epidemiology, Bloomberg
School of Public Health, 615 N. Wolfe St., Baltimore, MD, 21205 (firstname.lastname@example.org).
The Journal of Infectious Diseases2007;196:10–4
? 2007 by the Infectious Diseases Society of America. All rights reserved.
vudine (ZDV) was associated with reductions in mother-to-
child transmission (MTCT) of HIV at 6–8 weeks of age [2, 3].
NVP has a long half-life and might affect breast milk HIV load,
which has been shown to be associated with risk of HIV post-
natal transmission . Whether these simple regimens can in-
fluence the magnitude and timingof latepostnataltransmission
(LPT) associated with breast-feeding is unknown. In this study
in Malawi, we assessed the risk of LPT of HIV from 6–8 weeks
to 24 months and examined factors associated with LPT.
Subjects, materials, and methods.
domized clinical trials (NVP-ZDV [NVAZ] studies) were con-
ducted in Blantyre, Malawi [2, 3]. Infants were randomized to
receive orally a single dose of NVP (2 mg/kg weight) or NVP
(same single dose) plus ZDV (4 mg/kg weight) orally twice
daily for 1 week. Mothers of these infants received intrapartum
NVP if they presented early for delivery (early presenters) or
did not receive NVP if they presented late for delivery with
unknown HIV status (late presenters). All women were coun-
seled and consented for HIV testing, and those who were HIV
infected were enrolled after signing an informed consent form.
None of the women received antiretroviral treatment while
breast-feeding. Mother-infant pairs returned for follow-up vis-
its at infant age 1 and 6–8 weeks, and 3, 6, 9, 12, 15, 18, and
24 months. At each visit, maternal-infant information was ob-
tained, including breast-feeding status and type of feeding (ex-
clusive or mixed).
The NVAZ studies were approved by the University of Ma-
lawi College of Medicine Research and Ethics Committee and
the Johns Hopkins Bloomberg School of Public Health Com-
mittee on Human Research. Clinical care and referral were
available to all participants at the study clinics.
In the present study, LPT was defined as HIV transmission
occurring between 6–8 weeks and 24 months in breast-fed in-
fants (infant HIV RNA negative at 6–8 weeks and HIV infected
at a subsequent visit). All HIV-uninfected infants at 6–8 weeks
in the NVAZ studies were eligible. Infants were classified as
HIV infected if at least 1 HIV RNA test was positive or 2 ELISA
tests and Western blot test were positive at or after 18 months,
and infants were classified as HIV uninfected if HIV RNA tests
were negative after 6–8 weeks or if HIV serologic tests were
negative at or after 18 months. Infants with unclassifiable HIV
status were excluded. The estimated timing of infant HIV in-
fection was the midpoint between last negativeandfirstpositive
HIV test. Infant follow-up was censored at date of weaning;
extending this date to the next visit did not change the results.
Maternal baseline (enrollment) plasma viral load was mea-
Two concurrent ran-
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BRIEF REPORT • JID 2007:196 (1 July) • 11
Interval hazard of infant HIV infection. Estimates are based on Kaplan-Meier survival analyses.
Infant blood, collected on filter paper cards at birth and at
every follow-up visit, was tested for HIV RNA using NucliSens
QL (BioMerieux) [2, 3]. The HIV RNA tests were performed
at the University of North Carolina, Chapel Hill. Breast milk
viral load (HIV-1 RNA in whole breast milk) from all trans-
mitters (mothers of infants who became HIV infected) and a
matched sample of nontransmitters (mothers of HIV-unin-
fected infants) was measured using the BioMerieux HIV RNA
QT assay in accordance with the manufacturer’s instructions
 at a reference laboratory (University of North Carolina,
Chapel Hill). The samples from nontransmitters and trans-
mitters were matched on date of delivery and presentation of
the mother at delivery. Serial samples were tested starting from
the time of infant HIV infection and proceeding backward to
the time when the infant was not infected. NVP concentration
in breast milk and maternal plasma and infant plasma was
measured using a validated high-performance liquid chroma-
tography method  at the HIV Prevention Trials Network
Central Laboratory at the Johns Hopkins University,Baltimore,
Maryland. Maternal plasma NVP measurements were on sam-
ples collected at birth and 6–8 weeks from early presenters.
Infants’ plasma samples were also collected at the same time
Breast milk HIV RNA levels were log10transformed to com-
pare transmitters and nontransmitters at each visit using exact
tests. The probability of detecting differences in breast milk
viral load between transmitters and nontransmitters and be-
tween women who had received or had not received NVP were
statistically tested using robust covariance logistic regression
from the same individuals and multiple visits. Median values
risk of LPT and interval hazards were obtained for infants not
already HIV infected who became infected at 1.5–6, 6–12, 12–
ysis. HIV-free survival (infant alive and not HIV infected) was
estimated from the K-M analysis. Cox proportional hazard
models assessed the association of potential risk factors with
LPT; hazard ratios (HRs) and 95% confidence intervals (CIs)
were obtained. SAS software (version 9.1; SAS Institute) was
used for all statistical analyses.
Of 2000 infants enrolled in the NVAZ studies, 554
were excluded because they were HIV infected at birth or at
age 6–8 weeks ( ), died between birth and 6–8 weeksn p 322
(∼1.5 months) (
1.5 months ( ), or had no breast-feeding data (n p 189
). Of 1446 HIV-uninfected infants who presented at 1.513
months, 190 were excluded because HIV results were not avail-
able after 1.5 months. Therefore, 1256 infants were included
in the longitudinal analysis: 1158 HIV uninfected and 98 HIV
Figure 1 shows interval risks (hazard) of postnatal trans-
mission of HIV based on K-M analysis. Of the 2000 infants
enrolled in the NVAZ study, 190 (9.50% [95% CI, 8.21%–
10.79%]) were infected at birth. Of the remaining 1810 infants
who were not infected, 132 infants were HIV infected at or
before 1.5 months, corresponding to 8.43% (95% CI, 7.05%–
9.80%) from the K-M analysis. Among the 1256 infants in-
cluded in the longitudinal study and not previously infected,
the interval risk (hazard) of HIV infection was 1.22% (95%
CI, 0.61%–1.83%) during the period 1.5–6 months of age and
increased to 4.50% (95% CI, 2.89%–5.19%) during the period
6–12 months. After 12 months, there was a gradual decline in
hazard of HIV infection: 3.48% (95% CI,2.24%–4.70%)during
), lost to follow-up between birth andn p 30
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12 • JID 2007:196 (1 July) • BRIEF REPORT
Proportion of women with detectable breast milk viral load
12–18 months and 1.27% (95% CI, 0.33%–2.19%) during 18–
24 months. At 24 months, the cumulative risk of LPT of HIV
was 9.68% (95% CI, 7.80%–11.56%). Overall, 87.4% (9.68%
?1.22%/9.68%) of LPT infections occurred after 6 months.
The probability of HIV-free survival among infantsnotinfected
at 1.5 months of age was 98.7% at 6 months (95% CI, 98.1%–
99.3%), 94.6% at 12 months (95% CI, 93.2%–95.9%), 90.2%
at 18 months (95% CI, 88.4%–92.0%), and 87.4%at 24months
(95% CI, 85.3%–89.6%).
Baseline maternal plasma viral load was significantly asso-
ciated with LPT (adjusted HR [AHR], 3.67 [95% CI, 2.55–
5.27] per log10unit).Additionally,primiparity(AHR,4.82[95%
CI, 1.46–15.91]) and clinical mastitis (AHR, 4.94; [95% CI,
1.53–16.02]) were significantly associated with LPT. Other fac-
tors controlled for and not statisticallysignificantwerematernal
age, hemoglobin level, body mass index, early versus late pre-
sentation, and sex of infant.
Overall, 794 breast milk samples were tested for HIV RNA
from 313 women. The proportion of samples with detectable
breast milk viral load was consistently higher in transmitters
than nontransmitters at all visits (figure 2); these differences
were significant at each visit (P ! .02
) except visits at 3 (
), 18 ( .07
of detecting HIV in breast milk was lower during the period
1.5–9 months, compared with 12–24 months (nontransmitters:
odds ratio [OR], 0.38 [95% CI, 0.16–0.91]; transmitters: OR,
0.57 [95% CI, 0.38–0.99]). Among nontransmitters, the pro-
portion of women with detectable breast milk HIVRNAduring
1.5–3 months was significantly lower (
women who received NVP (early presenters) than in women
who did not receive NVP (late presenters); the numbers were
too small to compare differences at only 1.5 months.
NVP was detectable in all birth breast milk samples tested
for 33 women who received NVP intrapartum (early pre-
senters). In these samples, NVP concentrations were very high
(median, 1470 ng/mL; in 32/33 women NVP concentration
ranged from 679 to 4432 ng/mL). At 1 week, NVP was de-
tectable in breast milk in 45 (83.3%) of 54 samples tested
(median, 140 ng/mL; range, 29–460 ng/mL). At 6–8 weeks,
only 1 (1.3%) of 75 women tested had detectable NVP (41 ng/
mL) in breast milk. NVP in maternal plasma at 1.5 months
was undetectable in all 67 samples tested. At birth, plasma
samples from 31 infants of early presenting women were tested
for NVP concentration, and 25 (80.6%) had detectable NVP
), and 24 ( ) months. The probabilityP p .41P p .07
, exact test) inP p .03
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BRIEF REPORT • JID 2007:196 (1 July) • 13
(median, 674 ng/mL; range, 52–1609 ng/mL). At 1.5 months,
10 (4.3%) of 231 infants tested (born to early or latepresenters)
had detectable plasma NVP (median, 74 ng/mL; range, 35–811
This study shows that the risk of LPT associ-
ated with breast-feeding remains substantial. By age24 months,
the cumulative risk of HIV infection among infants who re-
ceived short antiretroviral prophylactic regimens and were un-
infected at 1.5 months was 9.7% (95% CI, 7.8%–11.6%). This
estimate is comparable to a LPT probability of 9.3% (3.8%–
14.8%) during 1–18 months reported from a meta-analysis
involving multiple African sites . The interval hazard of HIV
and LPT after 6 months accounted for 185% of infant HIV
infections (figure 1).
We speculate that several factors may explain the relatively
low risk between 1.5 and 6 months and the increase thereafter.
First, NVP being highly lipophylic and widely distributed
throughout the body  may have resulted in a more sustained
lowering of viral load in breast milk. Analyses of the breast
milk viral load andNVP concentrationdatainthepresentstudy
provide some clues but are inconclusive. For example, among
nontransmitters, the detection of breast milk HIV RNA during
the period 1.5–3 months was lower among women who re-
ceived NVP (early presenters) than in those who did not (late
presenters). However, consistent with results of other studies
, NVP levels were rarely detected after 1.5 months. Addi-
tional analyses (data not shown) did not show statistically sig-
nificant differences in association of early presenters (NVP re-
ceived intrapartum), compared with late presenters with LPT
after adjusting for infant prophylaxis and maternal plasmaviral
Second, we speculate that the appearance and then fading
of NVP resistance mutations may have influenced LPT in this
study. In the NVAZ studies, 64% of infants had detectableNVP
resistance mutations at 1.5 months , and other studies
showed that NVP resistance mutations fade and were no longer
detected by 12 months . NVP resistant virus might not be
easily transmitted or fit to adequately replicate in the infant
during the period 1.5–6 months, thus contributing to the low
risk of infant infection at this age. The rise in LPT after 6
months could be associated with disappearance of NVP resis-
tant virus and emergence of wild-type virus.
Third, exclusive breast-feeding has been shown to be asso-
ciated with lower postnatal transmission of HIV-1 in African
infants . In the present study, the frequency of exclusive
breast-feeding was high early postnatallyandgraduallydeclined
(99% at week 1, 90% at 1.5 months, 56% at 3 months, and
3% at 6 months). Although these data are unlikely to explain
the low risk before 6 months, this factor remains potentially
important because of misclassification and reporting errors of
breast-feeding. In the NVAZ studies, the median durations of
exclusive and mixed breast-feeding were 2 and 12 months,
The major risk factors associated with LPT were higher ma-
ternal plasma viral load,clinicalmastitis,andprimiparity.These
are consistent with findings of other studies, including earlier
studies from Malawi [14, 15]. A difficulty encountered when
evaluating interventions to curtail MTCT of HIV is how to
balance benefits of breast-feeding with risk of infant HIV in-
fection. Our findings suggest that if breast feedingwerestopped
by 6 months 185% of LPT could be prevented. HIV-infected
women should consistently be counseled about the risksof HIV
transmission through breast-feeding and adequately counseled
on safer feeding methods after weaning.
We are indebted to the mothers and children who participated in the
nevirapine-zidovudine studies. We are grateful to the nursing and technical
staff in Malawi for their excellent collaboration throughout this study. We
thank Teresa Parsons, Johns Hopkins University School of Medicine, for
performing the nevirapine assays.
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