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J Clin Microbiol. 2019 Apr 3. pii: JCM.00213-19. doi: 10.1128/JCM.00213-19. [Epub ahead of print]

Pigment Visibility on Rectal Swabs Used to Detect Enteropathogens: A Prospective Cohort Study.

Author information

1
Section of Pediatric Emergency Medicine, Alberta Children's Hospital, University of Calgary, Calgary, Alberta, Canada.
2
Department of Pediatrics, University of Calgary, Calgary, Alberta, Canada.
3
Department of Pediatrics, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada.
4
Women & Children's Health Research Institute (WCHRI), Edmonton, Alberta, Canada.
5
Provincial Laboratory for Public Health, Alberta Public Laboratories, Alberta Canada.
6
Department of Laboratory Medicine and Pathology, University of Alberta, Edmonton, Alberta, Canada.
7
Department of Pediatrics, Microbiology, Immunology and Infectious Diseases, Pathology & Laboratory Medicine and Community Health Sciences and the Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.
8
Department of Pediatrics, Division of Gastroenterology, & Nutrition, Washington University in St. Louis School of Medicine, St. Louis, Missouri, United States.
9
Departments of Laboratory Medicine and Pathology, University of Alberta, Edmonton, Alberta, Canada.
10
Department of Pathology & Laboratory Medicine, University of Calgary, Calgary, Alberta, Canada.
11
Sections of Pediatric Emergency Medicine and Gastroenterology, Department of Pediatrics, Alberta Children's Hospital, Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada. stephen.freedman@ahs.ca.

Abstract

Background: Data are lacking regarding the impact of visible pigment on rectal swab diagnostic accuracy. We describe the test characteristics of rectal swabs with and without pigment in children with gastroenteritis.Methods: Between December 2014 and September 2017, children <18 years with ≥3 episodes of vomiting and/or diarrhea in a 24-hour period and symptoms <7 days were enrolled through two pediatric emergency departments, and from a province-wide nursing telephone advice line in Alberta, Canada. Specimens were analyzed employing nucleic acid amplification panels. The primary outcomes were sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the rectal swabs using stool specimen results as the reference standard.Results: An enteropathogen was detected in 76.0% (1399/1841) of the paired specimens. 54.4% (1001/1841) of swabs had visible pigment. Respective enteropathogen detection characteristics of swabs with and without visible pigment were: 92.2% (95% CI 90.0%, 94.0%) vs. 83.7% (95% CI 80.5%, 86.4%) sensitive; 94.3% (95% CI 90.5%, 96.6%) vs. 91.2% (95% CI 86.3%, 94.5%) specific; 97.9% (95% CI 96.4%, 98.8%) vs. 96.5% (95% CI 94.5%, 97.8%) PPV; and 80.9% (95% CI 76.0%, 85.1%) vs. 65.8% (95% CI 60.0%, 71.1%) NPV. Processing swabs without visible pigment would increase identification of positives from 50.0% (682/1365) to 88.3% (1205/1365).Conclusions: There is a modest decrease in reliability of a negative test on swabs without evidence of pigment, but overall yield is significantly greater when they are not excluded from testing. Hence, rectal swabs without visible feces should not be routinely rejected from testing.

PMID:
30944189
DOI:
10.1128/JCM.00213-19

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