Laboratory diagnosis of autoinfection in strongyloidiasis.

Among 10,072 examinations of concentrated stools, Strongyloides stercoralis rhabditiform larvae were found in 93, and filariform larvae in four. In two of the four cases harboring filariform larvae, subsequent stools revealed only rhabditiform larvae, but filariform larvae continued to be found in the stools and sputum of the other two cases. It was concluded that only two of the cases were true autoinfections, and the other two apparent cases resulted from prolonged storage of unrefrigerated stools in the hospital ward. The importance of distinguishing true autoinfections from a free-living Strongyloides life cycle in stools is stressed.