A and WJ Rogan. 2003. Nonmalarial infant deaths and DDT
use for malaria control. Emerging
Infectious Diseases 9(8):960-964.
growing body of scientific evidence indicates that DDT may have
a substantial impact on infant mortality, by increasing the risk
of pre-term birth and by decreasing the duration of breast-feeding
after birth. In this paper, Chen and Rogan conclude that DDT
may cause a comparable increase in infant mortality through these
mechanisms as the decrease in infant mortality it causes by killing
mosquitoes and thus reducing malaria cases.
conclude that debates over the value of using DDT for malaria control
should incorporate consideration of the unintended consequences
authors acknowledge uncertainty in their calculations because the
available research does not yet prove conclusively that DDT causes
the effects on pre-term birth and breast-feeding. They argue, nonetheless,
that the findings are sufficiently plausible that they must be factored
into decisions about whether or not to use DDT for malaria control.
this article appeared just as an op-ed
was published in the New York Times recommending that DDT be
used in the US to fight West Nile Virus (WNV). While Chen and Rogan
do not address WNV in their paper, the analysis they advance is
equally, if not even more relevant here. In this case, the increases
in infant mortality due to DDT use would dramatically outweigh any
possible benefits that might result from using DDT to fight West
Nile Virus, because the number of deaths due to WNV is so low.
did they do? Chen and Rogan began with data from African
studies of DDT/DDE levels in people documenting the increase in
DDT/DDE levels that are caused by living in homes treated in malaria
control programs. They then calculated, based on the elevation in
DDE levels produced by treatment, how much infant mortality would
be expected to increase because of maternal DDT exposure based on
the following findings from the scientific literature.
risk of preterm birth
increases with the level of DDE measured in the mother's
serum. This finding, reported by a team of scientists from
the National Institute of Environmental Health Sciences
and they US Centers for Disease Control, found over a 3-fold
increase in preterm birth in the most exposed group. Preterm
birth, in turn, has a strong link to infant mortality. Babies
born before term are significantly more likely to die. [They
also are at risk to a range of adverse health conditions
through life (a cost not included in Chen and Rogan's calculation.]
duration of lactation decreases
as serum DDE levels increase. Two studies (data combined
in graph at right, from Chen and Rogan) both show that mothers
with higher serum DDE levels nurse their babies 40%-50%
less than mothers with little or no DDE.
shown in the graph to the left (from Chen and Rogan; data from
World Health Organization) An infant that is not breast feeding
at under two months of age is 5.8 times more likely to die than
an infant that is breast feeding. Several factors contribute
to this pattern. For example, children still breast feeding
are less likely to contract diarrheal diseases through exposure
to polluted water.
did they find?
and Rogan calculated that infant mortality would increase by 9%
because of preterm births, and by 20% because of shortened lactation.
the effect of preterm birth and shortened lactation, Chen and Rogan
calculated an overall increase of 20.5 deaths per 1000 infants.
By comparison, data from Africa indicate that malaria itself causes
20% of infant deaths in Africa (175 deaths per 1000 infants), with
additional deaths caused by maternal transmission of malaria (3-8%).
does it mean? The increase in infant deaths estimated by
Chen and Rogan to result from maternal DDE exposure is smaller but
comparable in magnitude to the number of children that die from
malaria. Therefore, according to Chen and Rogers, "the side
effects of DDT spraying might reduce or abolish its benefits from
the control of malaria in infants."
evaluating this comparison, several factors must be considered.
and Rogan used conservative assumptions in their calculations.
Hence the side effects of DDT spraying could be substantially
more adverse, even through just these two mechanims (shortened
lactation, increased preterm birth).
of DDT does not eliminate all childhood malaria. Hence the comparison
to total infant deaths caused by malaria is somewhat misleading;
the actual number of malarial deaths prevented by DDT would be
health effects of DDT/DDE (for example, the recent indication
exposure in the womb reduces fertility in women 30 years later)
would decrease DDT's net benefit further.
as they don't include adverse impacts of DDT use other than increased
infant mortality, they don't include beneficial impacts of DDT
use that result from decreased cases of childhood and adult malaria.
studies on which Chen and Rogan base their research were carried
out in the US and Mexico. They may not provide an accurate basis
for calculations extrapolated to Africa. The extrapolation could
be biased in either direction, high or low. As noted above, Chen
and Rogan used conservative procedures in the calculations to
avoid inflating the possible adverse effects of DDT.
studies have not established a causal relationship between DDE
serum levels and either preterm birth or shortened lactation.
The effects may be causal, and Chen and Rogan's calculations make
sense only if they are causal, but the nature of the epidemiological
methods used do not allow causal conclusions. This is a common
situation in epidemiology.
and Rogan's calculations challenge a prevailing assumption in considerations
about using DDT to control malaria, that the adverse effects of
DDT use are small compared to the benefits in avoided deaths. Instead,
Chen and Rogan show that the adverse effects are plausibly the same
order of magnitude as the benefits. Their work, while far from definitive,
raises a series of new questions about the wisdom of building malaria
control programs on DDT use, when not only are there likely to be
substantial adverse effects, but there are also affordable alternatives.
and Rogan's work is also of immediate relevance to a
proposal that DDT be used to fight West Nile Virus in the United
States. In this case, the possible benefits of DDT use are numerically
tiny compared to the likely adverse effects, even if the only adverse
effect of DDT is increased infant mortality.
one calculation, from the lead scientist at the National Institute
of Health who carried out the study
linking DDE to increased preterm birth, up to 15% of infant
mortality in the US during the 1950's and 1960's, may have been
caused by DDT. If that estimate is correct, elimination of DDT use
in the US is today avoiding approximately 66,000
each year. Even if that estimate is high by a factor of 10, that
would be 6,600 deaths, and this calculation does not include any
contribution of decreased lactation period. By comparison, West
Nile Virus last year caused approximately 300 deaths in the US.
BC and WJ Rogan. 1995. DDE and shortened duration of lactation
in a northern Mexican town. American
Journal of Public Health 85:504-508.
WJ, BC Gladen, JD McKinney, N Carreras, P Hardy, and J Thullen,
J Tingelstad and M Tully. 1987. Polychlorinated biphenyls
(PCBs) and dichlorodiphenyl dichloroethene (DDE) in human milk:
effects on growth, morbidity, and duration of lactation.
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