Measures of Malaria Burden after Long- Lasting Insecticidal Net Distribution and Indoor Residual Spraying at Three Sites in Uganda: A Prospective Observational Study
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Date
2016
Journal Title
Journal ISSN
Volume Title
Publisher
PLoS medicine
Abstract
Long-lasting insecticidal nets (LLINs) and indoor residual spraying of insecticide (IRS) are
the primary vector control interventions used to prevent malaria in Africa. Although both
interventions are effective in some settings, high-quality evidence is rarely available to evaluate
their effectiveness following deployment by a national malaria control program. In
Uganda, we measured changes in key malaria indicators following universal LLIN distribution
in three sites, with the addition of IRS at one of these sites.
Methods and Findings
Comprehensive malaria surveillance was conducted from October 1, 2011, to March 31,
2016, in three sub-counties with relatively low (Walukuba), moderate (Kihihi), and high
transmission (Nagongera). Between 2013 and 2014, universal LLIN distribution campaigns
were conducted in all sites, and in December 2014, IRS with the carbamate bendiocarb
was initiated in Nagongera. High-quality surveillance evaluated malaria metrics and mosquito
exposure before and after interventions through (a) enhanced health-facility-based
surveillance to estimate malaria test positivity rate (TPR), expressed as the number testing positive for malaria/number tested for malaria (number of children tested for malaria: Walukuba
= 42,833, Kihihi = 28,790, and Nagongera = 38,690); (b) cohort studies to estimate
the incidence of malaria, expressed as the number of episodes per person-year [PPY] at
risk (number of children observed: Walukuba = 340, Kihihi = 380, and Nagongera = 361);
and (c) entomology surveys to estimate household-level human biting rate (HBR),
expressed as the number of female Anopheles mosquitoes collected per house-night of
collection (number of households observed: Walukuba = 117, Kihihi = 107, and Nagongera
= 107). The LLIN distribution campaign substantially increased LLIN coverage levels at the
three sites to between 65.0% and 95.5% of households with at least one LLIN. In Walukuba,
over the 28-mo post-intervention period, universal LLIN distribution was associated
with no change in the incidence of malaria (0.39 episodes PPY pre-intervention versus 0.20
post-intervention; adjusted rate ratio [aRR] = 1.02, 95% CI 0.36±2.91, p = 0.97) and nonsignificant
reductions in the TPR (26.5% pre-intervention versus 26.2% post-intervention;
aRR = 0.70, 95% CI 0.46±1.06, p = 0.09) and HBR (1.07 mosquitoes per house-night preintervention
versus 0.71 post-intervention; aRR = 0.41, 95% CI 0.14±1.18, p = 0.10). In
Kihihi, over the 21-mo post-intervention period, universal LLIN distribution was associated
with a reduction in the incidence of malaria (1.77 pre-intervention versus 1.89 post-intervention;
aRR = 0.65, 95% CI 0.43±0.98, p = 0.04) but no significant change in the TPR
(49.3% pre-intervention versus 45.9% post-intervention; aRR = 0.83, 95% 0.58±1.18,
p = 0.30) or HBR (4.06 pre-intervention versus 2.44 post-intervention; aRR = 0.71, 95% CI
0.30±1.64, p = 0.40). In Nagongera, over the 12-mo post-intervention period, universal
LLIN distribution was associated with a reduction in the TPR (45.3% pre-intervention versus
36.5% post-intervention; aRR = 0.82, 95% CI 0.76±0.88, p < 0.001) but no significant
change in the incidence of malaria (2.82 pre-intervention versus 3.28 post-intervention;
aRR = 1.10, 95% 0.76±1.59, p = 0.60) or HBR (41.04 pre-intervention versus 20.15 postintervention;
aRR = 0.87, 95% CI 0.31±2.47, p = 0.80). The addition of three rounds of IRS
at ~6-mo intervals in Nagongera was followed by clear decreases in all outcomes: incidence
of malaria (3.25 pre-intervention versus 0.63 post-intervention; aRR = 0.13, 95% CI
0.07±0.27, p < 0.001), TPR (37.8% pre-intervention versus 15.0% post-intervention; aRR =
0.54, 95% CI 0.49±0.60, p < 0.001), and HBR (18.71 pre-intervention versus 3.23 postintervention;
aRR = 0.29, 95% CI 0.17±0.50, p < 0.001). High levels of pyrethroid resistance
were documented at all three study sites. Limitations of the study included the observational
study design, the lack of contemporaneous control groups, and that the interventions
were implemented under programmatic conditions.
Conclusions
Universal distribution of LLINs at three sites with varying transmission intensity was associated
with modest declines in the burden of malaria for some indicators, but the addition of
IRS at the highest transmission site was associated with a marked decline in the burden of
malaria for all indicators. In highly endemic areas of Africa with widespread pyrethroid resistance,
IRS using alternative insecticide formulations may be needed to achieve substantial
gains in malaria control.
Description
Keywords
Measures, Malaria, Insecticidal Net, Residual Spraying
Citation
Katureebe A, Zinszer K, Arinaitwe E, Rek J, Kakande E, Charland K, et al. (2016) Measures of Malaria Burden after Long-Lasting Insecticidal Net Distribution and Indoor Residual Spraying at Three Sites in Uganda: A Prospective Observational Study. PLoS Med 13(11): e1002167. doi:10.1371/ journal.pmed.1002167