Which diagnostic technique is most appropriate for concentrating and recovering nematode larvae from stool samples, particularly Strongyloides stercoralis?

• A. Kato-Katz thick smear
• B. Baermann funnel (Baermann) technique
• C. Direct saline smear
• D. Formalin-ether concentration

Answer: (B)

When diagnosing Strongyloides stercoralis from stool, you want a method that specifically isolates and concentrates living larvae. The Baermann funnel uses warm water and a porous support so that motile nematode larvae migrate out of the fecal material into the liquid and settle at the bottom for collection. This approach directly targets the larval stage—the rhabditiform larvae commonly found in Strongyloides infections—making them easier to identify under the microscope.

Other techniques focus on different targets or lack the concentration step. For example, methods designed to visualize eggs quantify helminth eggs rather than larvae and aren’t ideal for Strongyloides detection. Quick direct smears miss many infections due to low sensitivity. Formalin-ether concentration concentrates eggs and cysts but isn’t optimized for recovering live larvae and can distort them, reducing diagnostic accuracy for this parasite.