Quantitative assessment of geophagous behaviour as a potential source of exposure to geohelminth infection.

The most common form of pica, geophagy, has direct adverse nutritional effects and also exposes children to soil-borne infection. Existing methods for assessing geophagy are either inappropriate for field use (radiology) or unreliable (reporting). A new method is described, based on the measurement of soil-derived silica in stools. More than 90% of silica is excreted within one gut transit period of ingestion. The amount excreted is proportional to the amount ingested. Faecal levels of dietary silica (less than 2% dry wt stool) can be distinguished from levels due to geophagy (up to 25% dry wt stool). Studies in 2 children's homes in Jamaica showed that 33% and 66% of children were geophagous, ingesting up to 10 g soil day-1. The geophagy of less than 20% of the children accounted for greater than 60% of the total soil ingested. This overdispersion of exposure to soil-borne infection may contribute to the observed aggregation of geohelminth infection.