A Rational Approach to the Stool Ova and Parasite Examination

• Published in: Clinical infectious diseases 2006-04, Vol.42 (7), p.972-978
• Main Authors: Branda, John A., Lin, Tai-Yuan David, Rosenberg, Eric S., Halpern, Elkan F., Ferraro, Mary Jane
• Format: Article
• Language: English
• Subjects: Animals; Articles and Commentaries; Cryptosporidium parvum - isolation & purification; Dientamoeba - isolation & purification; Feces; Feces - parasitology; Giardia lamblia - isolation & purification; Hospitals; Humans; Infections; Infectious diseases; Iodine; Microbiology; Ova; Parasite Egg Count; Parasites; Parasites - drug effects; Parasitism; Patient assessment; Protozoa; Specimens; Testing
• ISSN: 1058-4838; 1537-6591
• DOI: 10.1086/500937

Background. Examination of multiple stool specimens per patient to rule out parasitic infection continues to be recommended in the literature. Attractive alternatives have been proposed, such as examination of a single specimen, but data to support their use have been inconclusive. Methods. We reviewed the results of comprehensive stool ova and parasite examinations performed during a 1-year period to determine the incremental value of examining >1 specimen. Next, we implemented rejection criteria, allowing analysis of only a single specimen in most cases, and studied the impact of the change by reviewing data from a subsequent year. Results. Prior to implementation of rejection criteria, 91% of parasites were detected in the first specimen submitted, although many clinical evaluations (72%) involved the submission of only 1 stool specimen. When at least 3 specimens were submitted, the sensitivity of examining the first in the series was 72%. Even the latter sensitivity provides negative predictive values of ∼98%, ∼97%, ∼95%, or ∼93% when the prevalence of parasites among those tested is 5%, 10%, 15%, or 20%, respectively. Examination of additional specimens after examination of the first specimen that yielded a positive finding revealed previously undetected parasites in only 10% of cases. After the application of rejection criteria, the parasite detection rate did not change significantly. Conclusions. Comprehensive examination of a single stool specimen is sufficient for most patients, when the prevalence of infection among the tested population is up to 20%. Rational use of the stool ova and parasite examination relies on communication between clinician and laboratory, and retention of deferred specimens in case examination of additional specimens is clinically warranted.