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Olaf Müller a Department of Tropical
Hygiene and Public Health, Ruprecht Karls University, 69120 Heidelberg,
INF 324, Germany, b Centre de Recherche en Santé de Nouna, Nouna,
Burkina Faso, c Centre National de Recherche et
de Formation sur le Paludisme, Ouagadougou, Burkina Faso, d Centre Français sur la
Population et le Dévelopement, 75270 Paris, Cedex 06, France
Correspondence to: O Müller olaf.mueller{at}urz.uni-heidelberg.de
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Abstract |
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Objective:
To study the effects of zinc
supplementation on malaria and other causes of morbidity in young
children living in an area holoendemic for malaria in west Africa.
Design:
Randomised, double blind, placebo controlled efficacy trial.
Setting:
18 villages in rural northwestern Burkina Faso.
Participants:
709 children were enrolled; 685 completed the trial.
Intervention:
Supplementation with zinc (12.5 mg zinc
sulphate) or placebo daily for six days a week for six months.
Main outcome measures:
The primary outcome was the
incidence of symptomatic falciparum malaria. Secondary outcomes were
the severity of malaria episodes, prevalence of malaria parasite, mean
parasite densities, mean packed cell volume, prevalence of other
morbidity, and all cause mortality.
Results:
The mean number of malaria episodes per child (defined as a temperature
37.5°C with
5000 parasites/µl)
was 1.7, 99.7% due to infection with Plasmodium
falciparum. No difference was found between the zinc and placebo
groups in the incidence of falciparum malaria (relative risk 0.98, 95%
confidence interval 0.86 to 1.11), mean temperature, and mean parasite
densities during malaria episodes, nor in malaria parasite rates, mean
parasite densities, and mean packed cell volume during cross sectional surveys. Zinc supplementation was significantly associated with a
reduced prevalence of diarrhoea (0.87, 0.79 to 0.95). All cause mortality was non-significantly lower in children given zinc compared with those given placebo (5 v 12, P=0.1).
Conclusions:
Zinc supplementation has no effect on
morbidity from falciparum malaria in children in rural west Africa, but it does reduce morbidity associated with diarrhoea.
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What is already known on this topic
What this study adds
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Introduction |
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The annual incidence of malaria is about 300-500 million cases, causing between 1.5 and 2.7 million deaths.1 Tropical Africa accounts for 90% of the morbidity and mortality attributed to malaria; severe disease and death mainly occur among infants in remote rural areas. 2 3 Prevailing poverty, lack of functioning health services, climatic and environmental change, and the rapid spread of chloroquine resistance contribute to a deteriorating malaria situation in Africa.1-6
Zinc deficiency is common in children in developing
countries.7 It has been associated with an increased
susceptibility to a variety of infections because of its effects on the
immune system.8 In several studies, mainly from Asia and
Latin America, zinc supplementation has been shown to have therapeutic
and preventive effects on acute and chronic diarrhoea, dysentery, and
pneumonia.9-22 Only two studies have provided data on the
possible efficacy of zinc supplementation in reducing morbidity from
malaria.
23 24
We aimed to test the hypothesis that zinc
supplementation reduces morbidity from falciparum malaria in African children.
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Participants and methods |
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Study area
Our study took place between June and December 1999 in the Nouna
district of northwestern Burkina Faso. This area is a dry orchard
savanna, populated mainly by subsistence farmers of different ethnic
groups. Malaria is a major cause of morbidity and mortality in children
in this region, with most transmission occurring during and shortly
after the rainy season from June to October.
Study design
Our study was designed as a randomised, placebo controlled, double
blind efficacy trial. We identified eligible children from the
demographic surveillance system of the Centre de Recherche en Santé
de Nouna.26 Eligible children were aged between 6 and 31 months at enrolment and were permanent residents in 18 of the 39 villages of the study area. We recruited children by lottery (names
were drawn blindly at random from a box); 30 from 12 small villages and
60 from six larger villages. Children were allocated zinc or placebo in
blocks of 30 (15 zinc, 15 placebo) by computer generated randomly
permutated codes (prepared by the World Health Organization). We
excluded children with serious underlying illness, and we excluded from
the final analysis those who were absent from the study area for more
than 14 consecutive days. Assuming a mean of one malaria episode per
child per season and allowing for 20% loss to follow up, we used a
sample size of 720 children to detect a 20% reduction in episodes of
falciparum malaria with 90% power (
=0.05).
Laboratory procedures
Blood was usually taken by finger prick, and the packed cell
volume was measured in the field with a portable microhaematocrit
centrifuge (Compur Microspin, Bayer Diagnostics, Germany). Blood films
were kept in closed slide boxes until transportation to Nouna (two or
three times a week during longitudinal follow up and daily during cross
sectional surveys). They were stained with Giemsa at the Nouna hospital
laboratory and transported to the Centre National de Recherche et de
Formation sur le Paludisme in Ouagadougou for reading. The films were
examined by two laboratory technicians and checked by a third
investigator in cases of discrepancy. Blood films were analysed for the
species specific parasite density per microlitre by counting against
500 white blood cells and multiplying by 16 (assuming 8000 white blood
cells per microlitre of blood). If no parasites were seen in 400 fields
on the thick film a negative result was declared. A 10% random sample
of blood films was re-examined at the laboratory of the Heidelberg
School of Tropical Medicine, showing an overall 97% concordance for
Plasmodium falciparum parasitaemia. Venous blood was kept
in a cold box until centrifugation on the same day in Nouna. Serum
samples were stored at
20°C until zinc determination at the
Heidelberg University laboratory by flame atomic absorption
spectrometry (Perkin-Elmer 1100 B, Germany).
Statistical analysis
Data forms were checked by supervisors before computer entry
(version 97, Microsoft Access) at the Centre de Recherche en
Santé de Nouna. Parasitological data were entered into EpiInfo
(version 6.0) at the Centre National de Recherche et de Formation sur
le Paludisme, and the data were transferred to the Centre de Recherche
en Santé de Nouna. All data were checked for range and consistency,
and all parasitological data and data from cross sectional surveys were
double entered. Any differences were resolved by checking against the
original case record forms. The randomisation code was broken after the
database was closed. Analysis was by intention to treat.
2
analysis to test differences in distributions and t tests to compare arithmetic means. All analyses were done with SAS (version 6.12).
Ethical aspects
We received ethical approval for our study from the ethical
committee of the Heidelberg University Medical School and the Ministry
of Health in Burkina Faso. The trial was explained to the Nouna health
district authorities, the villagers, and the head of each participating
compound. Oral consent was obtained from the parents and carers of the
children before enrolment. Sick children seen during surveys or visits
by the supervisors were treated in the village or referred to Nouna
hospital free of charge.
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Results |
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Of 713 eligible children (one village had only 23 children of the required age group), 709 were enrolled and randomised to either zinc (n=356) or placebo (n=353). The children were not treated for 4349 days in total owing to absence, an average of 6.3 days per child (2163 zinc, 2186 placebo). Overall, 661 of 685 children (96%) were examined during the cross sectional surveys (figure).
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Table 1 shows the characteristics of the children at baseline in June. The two groups were similar, except for the children being slightly older in the zinc group (18.7 v 17.5 months, P=0.03). At baseline 26% of the children were aged 6-12 months, 27% were 13-18 months, 26% were 19-24 months, and 21% were 25-31 months.
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The prevalence of malnutrition was high at baseline (table 2), with 36.3% of children below -2 z score for height for age (stunting) and 24.6% below the -2 z score for weight for height (wasting). The effects of zinc on anthropometric measurements will be published elsewhere.
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Serum zinc values paired for June and September were available for 81 children (41 zinc, 40 placebo; table 2). Mean zinc concentrations at baseline were 11.7 µmol/l, with no differences between the two groups, and 72% of the children were zinc deficient according to the reference laboratory's threshold of 13.0 µmol/l. After three months (mid-study survey), children in the zinc group had significantly higher serum zinc concentrations than children in the placebo group (15.3 v 12.4 µmol/l, P=0.005), and the proportion of zinc deficient children significantly declined in the zinc group but not in the placebo group (11/41 v 28/40, P=0.0001).
Spleen enlargement (Hackett score >1) was common at baseline and increased significantly until the end of the study (87% in zinc group v 98% in placebo group, P=0.001; table 2 ). At the height of the rainy season (September) a quarter of the children reportedly slept under an untreated mosquito net the night before their visit, with no significant differences between the zinc and placebo groups (24% v 27%). Parasitological results were available for 511 of 661 (77%) and 615 of 661 (93%) children at baseline and at the end of the study, respectively (table 2). Overall, P falciparum was the most common parasite (99%), and most of the children who had P malariae (6%) and P ovale (10%) also had P falciparum. The prevalence of falciparum malaria (1.4% in zinc group v 6.2% in placebo group, P=0.001) and of P falciparum, P malariae, and P ovale parasitaemia (62.8% v 89.6%, P=0.001; 4.2% v 13.2%, P=0.001; 0.6% v 20.2%, P=0.001), and the mean density of P falciparum (2909 v 7954, P=0.001) increased significantly over the study. Mean packed cell volume values, measured in 70 children (39 zinc, 31 placebo) at baseline and at follow up, significantly decreased from 32.0 to 29.1 over the study period (P=0.001). No differences were found in clinical or parasitological characteristics between the two groups, either at mid-study (data not shown) or at the end of the study.
Table 3 shows the results for morbidity at follow up in the
longitudinal study. Parasitological results were available for 2065 of
2324 (89%) febrile episodes. Over the six months of the study, the
mean number of episodes of falciparum malaria a month was 0.38 (parasite density
1/µl), 0.28 (
5.000/µl), and 0.02 (
100 000/µl), with no differences between the zinc and placebo groups at any of the respective three parasite thresholds (relative risk 0.99, 95% confidence interval 0.89 to 1.11, P=0.94; 0.98, 0.86 to
1.11, P=0.77; 1.00, 0.64 to 1.60, P=0.91). This finding remained the
same after analysis of the effects of zinc on the incidence of P
falciparum by age group (data not shown). No difference was found
between the two groups for mean temperature (38.3°C in zinc group
v 38.3°C in placebo group) and mean parasite density (44 529 v 44 316) during episodes of falciparum
malaria (
37.5°C with
5000
parasites/µl).
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Table 3 also shows the effects of zinc supplementation on the number of reported days with other morbidity outcomes. No differences were found in the number of days with fever (relative risk 1.01, 0.95 to 1.07, P=0.62) and the number of days with cough (1.05, 0.97 to 1.15, P=0.22) between the two groups, but the number of days with diarrhoea was significantly lower in the zinc group (0.87, 0.79 to 0.95, P=0.002).
More children in the placebo group than zinc group died during the
study (12 v 5), but this difference did not reach
significance. The estimated relative risk in the survival analysis with
a proportional hazards model was 0.41 (0.15 to 1.19, P=0.1). The
relative risk did not change appreciably (0.47) when covariates were
adjusted for.
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Discussion |
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We found no evidence for zinc supplementation being effective against falciparum malaria in a population of west African children with a high prevalence of malnutrition and zinc deficiency. Recipients of zinc were no different for number of episodes of falciparum malaria or any other malariometric measurement than the recipients of placebo. This was so for all age groups and was consistently seen during both the longitudinal study and the cross sectional surveys.
Our study was a large randomised controlled trial, which had reasonable power to detect a moderate efficacy of the intervention. Case detection was intense and sustained, loss to follow up was small, and individual randomisation made systematic errors unlikely. Dilution of the intervention through fieldworkers mixing up the allocation of zinc or placebo also seems unlikely owing to training and supervision. Moreover, the intervention was followed by a significant increase in serum zinc concentration in the zinc group, whereas zinc concentration remained unchanged in the placebo group.
Our results do not confirm the findings of two community based studies on zinc supplementation and malaria. 23 24 One study, on children aged 7-28 months in the Gambia, showed 32% fewer clinical episodes of malaria in children given zinc compared with those given placebo after follow up over 15 months.23 This was, however, a small study on 110 children matched for age and sex, zinc supplementation was given only twice weekly, no information was provided on the methods for diagnosis of malaria, and the effects on malaria were only of borderline significance. The other study looked at the effects of zinc supplementation on morbidity from malaria in 274 children aged 6-60 months in Papua New Guinea.24 The children were randomly assigned to 10 mg zinc gluconate or placebo for six days a week for 10 months. The trial reported a 30-35% reduction in attendances to a health centre due to malaria in those children receiving zinc compared with those receiving placebo.
Even mild zinc deficiency can impair multiple mediators of host immunity.8 Some evidence shows that zinc deficiency predominantly affects the cell mediated immune system.28-32 In this context, our inability to show an effect of zinc supplementation on morbidity from malaria may provide evidence for cell mediated immunity being less important in malaria in humans. Furthermore, such a hypothesis would be supported by the overwhelming evidence for malaria not behaving as an opportunistic infection in African children with HIV or AIDS.33-35
Overall, 17 of the 709 (2.4%) children died during the study, which
confirms the unacceptably high level of childhood mortality from
malaria in rural African regions.1-3 We found a tendency for zinc to be protective against all cause mortality, which could be a
real finding given the known effects of zinc on gastrointestinal and
respiratory infections.9-22 This is supported by our
finding of a significantly lower prevalence of diarrhoea in children
given zinc rather than placebo. Our study was not designed to look in detail at the effects of zinc on other causes of morbidity, and such
findings must be interpreted with caution.
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Acknowledgments |
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We thank Walter Fiehn of Heidelberg Medical School for determining the serum zinc values, the team of the Heidelberg Tropical Institute for quality control of the malaria slides, Brian Greenwood for his advice during the design and implementation of the study, the staff of the Centre de Recherche en Santé de Nouna, and the children and their parents.
Contributors: OM was responsible for the overall coordination of the study and contributed to the study design, enrolment and examination of the children, field supervision, and data analysis; he will act as guarantor for the paper. HB was responsible for data analysis and contributed to the study coordination. ABvZ was responsible for the coordination and supervision of the fieldwork and contributed to the analysis and interpretation of the data. YY was responsible for the management of the data in Nouna and contributed to the design of the study. DAD contributed to the design, field supervision, and laboratory supervision of the study. ATK contributed to the coordination, field supervision, and analysis and interpretation of the data. AG and BK contributed to the design and coordination of the study. MG contributed to the study design and coordination and data analysis. All authors contributed to the writing of the paper.
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Footnotes |
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Funding: The World Health Organization and the Deutsche Forschungsgemeinschaft (SFB 544, control of tropical infectious diseases).
Competing interests: None declared.
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(Accepted 22 March 2001)