How to Obtain Samples for Diagnosis of Urinary Schistosomiasis
For urinary schistosomiasis (S. haematobium), collect a midstream urine sample, ideally between 10 AM and 2 PM when egg excretion peaks, and filter 10 mL through a polycarbonate or Nytrel filter for microscopic examination of eggs. 1, 2
Optimal Sample Collection Timing and Method
Collect urine samples between 10 AM and 2 PM when egg excretion is highest in S. haematobium infection, as this timing maximizes diagnostic sensitivity 3
Obtain a midstream clean-catch urine specimen from cooperative patients who can follow instructions 4
For patients unable to provide clean-catch samples, use a freshly applied clean condom external collection system with frequent monitoring for men, or perform in-and-out catheterization for women 4
Sample Processing for Microscopy
Filter 10 mL of urine through a polycarbonate filter (Nuclepore) or Nytrel filter to concentrate eggs for microscopic examination 2, 5
After filtration, the filter paper can be dried and stored at room temperature for several months before examination, making this method practical for field settings where immediate processing is not feasible 2
Examine the entire filter under microscopy to count S. haematobium eggs, with counts expressed as eggs per 10 mL of urine 3
Alternative and Adjunctive Diagnostic Approaches
Urine Reagent Strips (Indirect Method)
Use urine reagent strips (Hemastix) to detect microhaematuria as a proxy for infection, though this method has significant limitations in light infections 6, 7, 3
Sensitivity of reagent strips is only 50-59% for ultra-light infections (1-5 eggs/10 mL) but increases to 95% in heavy infections (≥500 eggs/10 mL) 6, 3
Combining macrohaematuria (visible blood), microhaematuria, and proteinuria increases diagnostic accuracy to 63% sensitivity and 93% specificity, making this useful for rapid screening in resource-limited settings 6
Antigen Detection Methods
Collect urine for Point-of-Care Circulating Cathodic Antigen (POC-CCA) testing, though this assay is less reliable for S. haematobium than for S. mansoni 4, 1
The POC-CCA assay can be performed on-the-spot or on stored urine samples and does not require microscopy or highly trained personnel 4
Molecular Methods
Filter urine through heavy Whatman No. 3 paper and dry for DNA extraction, which can detect S. haematobium-specific DNA fragments (Dra 1,121 bp repeat) with higher sensitivity than egg detection 2
DNA detection identified 57% of infections compared to only 49% by egg detection in one study, and detected 7 of 20 egg-negative samples that were truly infected 2
Critical Diagnostic Pitfalls
Ultra-light infections (1-5 eggs/10 mL) comprise 35-47% of all infections in low-transmission areas like Zanzibar, and these are frequently missed by both microscopy and reagent strips 3
Even experienced microscopists have discrepant readings on 6-8% of slides, with 77-84% of these discrepancies occurring in ultra-light infections 3
Single urine examinations miss many infections—in elimination settings, consider repeat sampling or more sensitive antigen/molecular methods 1, 3
Eggs may continue to be excreted from tissue deposits even after worms are killed, so positive microscopy does not always indicate active infection 1