GSTM1 and anemia (phenotype): Whereas the National MIS used a HemoCue to estimate haemoglobin concentration and defined anaemia as Hb < 11.0 g/dL in under fives or Hb < 11.5 g/dL in those of 5–11 years, we used a microematocrit centrifuge to estimate the PCV of the children and defined anaemia as PCV < 30%.