Background: Hookworm eggs identification and quantification is usually carried out by Kato-Katz method. However various structures present in the smear may be confused with eggs of such parasites.

Objective: To document the presence of structures in Kato-Katz slides that could initially be misinterpreted as hookworm eggs.

Method: 497 faecal samples were analysed by Kato-Katz technique, diphasic concentration technique, agar-plate coprocultive and larvae obtained were analysed by PCR and characterized by sequencing.

Result: Hookworm-like eggs were found in 159 (32%) of the samples by Kato Katz, finally identified as Caenorhabditis elegans by PCR technique.

Conclusion: The diagnosis of human hookworm eggs, only by the use of Kato Katz technique can lead to false positives because of similarities with eggs of other free-living worms, from wet soils like those of Rwanda that could contaminate stool samples.