tuberculosis (TB) increased the risk of mother-to-child HIV transmission 2.5
fold, Amita Gupta and colleagues reported in a study published in the February 1st edition of the Journal of Infectious
authors undertook an analysis of data from 783 mother-infant pairs enrolled in
a prospective, randomized, placebo-controlled six week extended dose nevirapine
prophylaxis trial (SWEN) (includes 41 pairs in an ancillary cohort) from August
2002 to September 2007 in a large, urban public teaching hospital in India.
is recognised as the leading infectious cause of death among women worldwide
and the most important cause of disease and death among women with HIV in
resource-poor settings. Women account for approximately 70% of all HIV infections
where heterosexual transmission is dominant. The
highest number of HIV and TB infections occurs in women of child-bearing age
(15-49 years). TB and HIV-TB co-infection during pregnancy and after birth
often result in infant and maternal disease and death.
an accompanying editorial Dr Ben Marais, a specialist in child health at Stellenbosch University, South Africa, notes that while it
is generally recognised that people with HIV are at greater risk for TB
infection, the role that TB plays in HIV transmission and disease progression
is not fully appreciated.
independent risk factors for mother-to-child HIV transmission include maternal
viral load, CD4 cell count, length of breastfeeding, antiretroviral treatment
and malaria co-infection.
purpose of the analysis of TB and HIV transmission within the SWEN study was to
determine the effect of maternal TB on the risks of vertical HIV transmission
from mother to child.
primary goal of the SWEN study was to compare extended nevirapine versus
single-dose nevirapine to reduce vertical HIV transmission among breastfed
infants. The authors assessed the effect of maternal TB on the risk of vertical
transmission during pregnancy and in the 12 months after delivery.
the 783 mothers 33 had TB: three prevalent (or TB diagnosed before entering the
study) and 30 incident (or a new TB diagnosis during follow-up). Of the 33, 10 (30%) transmitted HIV to their
infants compared to 87 out of a total of 750 mothers without TB (12%). (Odds
ratio 2.51, CI: 95% 1.05-6.02; P= 0.04)
points out that the numbers with incident TB (30 out of 780) translates to a TB
incidence rate of 3846 cases/100,000 population/year, which he notes is
the authors do not speculate on the reasons for this high incidence rate, there is some evidence in the study
population to suggest that late diagnosis of TB was a problem among women in
the trial, implying the potential for considerable transmission of TB within
health care facilities attended by women taking part in the trial.
authors suggest reasons why maternal TB might be associated with MTCT in a
breastfeeding population. Maternal TB may increase maternal HIV infectiousness
through an increase in viral load; an increase in viral load in breast-milk
and; in the same way that studies have shown placental malaria and
sexually-transmitted infections increase transmission by the mechanism of
immune activation and infectiousness.
notes increased viral load because of immune stimulation in mothers with TB
accounted for much of the increased risk. However, he points out as do the
authors that the increased risk remained after multivariate analysis corrected
for maternal (viral load, CD4 cell count, antiretroviral use) and infant
factors (nevirapine administration and breastfeeding duration).
The authors stress that while maternal TB was
associated with a small fraction of MTCT it is preventable with what is referred
to as the 3 I’s, a TB control strategy recommended by the World Health
Organization (WHO): improved infection control, improved community-based
intensive case-finding, and implementation of isoniazid prevention therapy.
study showed that maternal TB was independently associated with an increased risk
of MTCT in women who breastfed and had a TB diagnosis less than six months
notes that most of the infants were diagnosed with HIV at delivery (suggesting transmission
during pregnancy) and very close to maternal TB diagnosis. He stresses that not
only has the study shown an association between maternal TB and infant HIV
diagnosis but the clustering of these two events suggests a causal
include, according to the authors, the analysis is a secondary endpoint of the
clinical trial which was not originally designed to test the hypothesis of
maternal TB as a risk factor for mother to child transmission; not all TB
diagnoses were culture-confirmed.
underscores that the very high TB disease and transmission risk “provides
additional motivation to carefully monitor all HIV-infected women for TB during
and after pregnancy.”
concludes “renewed global focus on maternal and child health…is welcomed…but
adequate recognition must be given to the importance of TB control and
prevention in areas where TB is endemic.”