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The report by Sunyer et al 1 of an association between malaria parasites in umbilical cord blood and wheezing at 4 years of age is of considerable interest. Their interpretation of these findings is related to an association with unspecified intrauterine events. A further explanation is that babies with cord parasitaemia were more likely to be born preterm. The importance of preterm delivery in predisposing to recurrent cough and wheeze in children (5–11 years) living in a non-malarious area has been reported, and premature babies of asthmatic mothers were found to be at very high risk of childhood symptoms.2 Redd et al have also observed, in a large cohort study from Malawi, that malaria cord parasitaemia was significantly associated with preterm delivery (odds ratio (OR) 2.51, 95% confidence interval 1.45 to 4.18), intrauterine growth retardation (OR 2.49, 95% CI 1.47 to 4.06), and maternal HIV infection (OR 2.87, 95% CI 1.74 to 4.60).3 These factors may confound the association of cord parasitaemia with wheezing reported by Sunyer et al. Malaria during pregnancy is well described as a major cause of prematurity and growth retardation in babies born in malarious areas,4 and it would be helpful to know the birth status (preterm, low birth weight, or growth retarded) of the children from the Tanzanian study. In view of the high attributable risk of malaria related low birth weight in developing countries, it will be important to ascertain its possible influence on the risk of asthma during childhood.
authors' reply We thank Professor Brabin and Dr Rizwan for the suggestion of potential confounding by preterm delivery in the association between prenatal malaria and childhood wheezing. We had the opportunity to analyse the role of low birth weight, an objective surrogate measure of preterm delivery, and found that 15% of the 523 newborn infants weighed less than 2500 g. Maternal malaria was related to low birth weight (26% of women with parasitaemia gave birth to babies weighing <2500 g compared with 12% of women without parasitaemia, odds ratio 2.47, 95% CI 1.62 to 3.77). However, low birth weight was not related to wheezing at 4 years of age (15% and 14% of newborn infants with low and normal birth weight, respectively, developed wheezing, p=0.9). The association between parasites in cord blood and wheezing at 4 years of age was not confounded by birth weight (either as a continuous or a dichotomous variable), nor was birth weight or gestational age associated with asthma in five consecutive birth cohorts of Finnish adolescent twins.1-1 The explanation of why malaria infection during pregnancy is related to wheezing may involve mechanisms other than those related to low birth weight.