As soon as possible after discharge from hospital, patients were visited at home by a project field worker to collect information on social economic and environmental risk factors that may predisposes an individual child to develop severe anaemia. A housing survey was conducted during this visit to determine possible risk factors for malaria which might act as confounders in determination of the primary trial end-point. Field workers interviewed the parents/guardians of study subject to record characteristics about the house that might influence mosquito biting behaviour. These items included building material, an evaluation of the presence of eaves, impregnation and condition of bed nets. During the visit, parents were encouraged to protect the study child with a bed net.