Relative contribution of day-to-day and intra-specimen variation in faecalegg counts of Schistosoma mansoni before and after treatment with praziquantel

There is evidence that faecal egg counts of Schistosoma mansoni vary consid erably from day to day, which results in poor sensitivity of single stool r eadings. Intra-specimen variation of S. mansoni egg counts may also be cons iderable, but has previously been considered as the less important componen t. We quantified the relative contribution of these two sources of variatio n among 96 schoolchildren from an area in Cote d'Ivoire highly endemic for S. mansoni. Stool specimens were collected over 5 consecutive days, and 5 e gg-counts were made in each specimen by the Kato-Katz technique. The point prevalence of the first sample was 42.7 % and the cumulative prevalence aft er the maximum sampling effort was 88.5 %. Using generalized linear mixed m odels we found that the presence of S. mansoni eggs in a stool sample varie d much more between days than within specimens, indicating that stool sampl e examination over multiple days is required for accurate prevalence estima tes. However, using the same approach, we found that among infected childre n intra-specimen variation in egg counts was 4.3 times higher than day-to-d ay variation. After praziquantel administration, day-to-day variation was m ore important than before, since most infections were very light and thus l ikely to be missed altogether by stool examination on a single day. We conc lude that diagnostic sensitivity in high transmission areas is maximized by making several stool readings on several days, but examining 1 stool speci men several times can make reasonable estimates of infection intensity.