The prevalence of fever increased with the severity of anaemia: 3 % in participants with an Hb ≥11 g/dL, 5 % with 8 ≤ Hb < 11 g/dL and 9 % in the group with Hb <8 g/dL (2 d.f.; p = 0.002). This evidence concerns the gene GSTM1 and anemia (phenotype).