Diagnosis of Oesophagostomum bifurcum and hookworm infection in humans: day-to-day and within-specimen variation of larval counts.

Oesophagostomum bifurcum, as well as hookworm infections are hyperendemic among humans in northern Togo and Ghana. For parasite-specific diagnosis a coproculture is obligatory, because only the infective larvae, and not the eggs, can be distinguished morphologically. The sensitivity of duplicate coprocultures from a single stool sample was found to be above 90% in comparison to a gold standard of 10 coprocultures made from a single stool specimen. Prevalence of infection with O. bifurcum and hookworm further increased with the number of coprocultures made from each individual stool. Notwithstanding the high sensitivity, intensity of infection per individual varied considerably from day-to-day and the number of larvae found in different samples out of 1 stool also varied highly, both showing a heterogeneous distribution. Surprisingly, daily fluctuation and within-specimen variation could not be differentiated from each other, probably because of the variation created by the coproculture technique. To estimate the intensity of infection, it is sufficient to make repeated coprocultures from only 1 individual stool sample. Laborious collection of stool samples on subsequent days does not give better estimates of the individual infection status.