Factors associated with detecting pathogenic intestinal parasites in multiple stool microscopy samples: a retrospective cross-sectional study

Determining the optimal number of stool samples for accurate parasite detection is crucial in healthcare. However, previous studies have reported conflicting results. This study investigated factors associated with the detection of pathogenic intestinal parasites in additional stool microscopy examinations. This retrospective cross-sectional study at a tertiary care hospital outpatient clinic included patients who submitted three stool samples between 2012 and 2021 and had at least one pathogenic intestinal parasite-positive stool sample. Diagnostic yields for one, two, and three stool specimens were the primary outcome. The secondary outcome was the identification of factors associated with the time to the first positive stool microscopy result, which was analysed using ordinal logistic regression. Among the 103 infected patients, compared with the infection detection rate in the first specimen, the rate increased with the second specimen and further increased with the third specimen, achieving a cumulative detection rate of 100%. Some parasites, such as hookworms, were easily detected in the first sample. However, more than half the patients infected with Trichuris trichiura and all patients infected with Isospora belli were missed if only one stool specimen was collected. Immunocompetent hosts were significantly more likely to have pathogenic intestinal parasites detected in later stool specimens (adjusted ordinal odds ratio = 3.94 [95% confidence interval: 1.34-14.05]). Collecting multiple stool specimens was associated with a higher likelihood of detecting pathogenic intestinal parasites, particularly in immunocompetent patients. Clinicians may request a second or even a third sample if the first is negative.