The effect of counting duration on quantitative fecal egg count test performance

Area of Science:

• Equine parasitology
• Diagnostic methods in veterinary medicine
• Parasitic disease diagnostics

Background:

• Fecal egg counts are crucial for diagnosing equine parasites, with the McMaster test widely recommended.
• Manual counting is susceptible to human error, particularly under time pressure in clinical settings.
• The impact of reduced counting duration on McMaster test accuracy and precision remains unquantified.

Purpose of the Study:

• To evaluate the effect of restricted counting time on McMaster fecal egg count performance.
• To compare McMaster test results with an automated method under time constraints.
• To assess the impact of counting only one grid versus two on test precision.

Main Methods:

• Fifteen equine fecal samples with varying strongylid parasite loads were used.
• Subsamples were counted manually using the McMaster technique with restricted (1-2 min) and un-restricted times.
• A single-grid count was also assessed, and results were compared to an automated counting method.

Main Results:

• Reducing counting time to one minute decreased manual egg counts by 50-60% (p<0.001).
• Two-minute counting still resulted in ~10% lower counts (p<0.001) and reduced precision (CVs) by one-third.
• Counting a single grid also decreased precision, while the automated method showed superior and consistent precision.

Conclusions:

• Modifications to standard McMaster test procedures to save time significantly impair accuracy and precision.
• Analysts must carefully weigh the trade-offs between practicality and diagnostic quality when altering counting protocols.
• The automated method offers greater precision and is less affected by time pressures compared to manual counting.