Lead poisoning and hookworm infection as multiple factors in anaemia

A retrospective study was carried out in a rural area of north-eastern Brazil, to search for interactions between biological and chemical agents present in the environment as causes of anaemia. A lead smelter situated in a hookworm endemic area provided the opportunity to look at the effect of this double exposure in relation to laboratory defined anaemia, by comparing the odds ratios in different subgroups of 109 "cases" and 107 "controls". The subgroup with both hookworm infection and chronic lead poisoning--measured by the concentration of delta-ALA excreted in urine--had an odds ratio of developing anaemia five times greater than individuals with neither. Although a synergistic effect could not be demonstrated, the additive effect of the two conditions placed this group in a higher risk category.