SAN DIEGO – Clinicians who treat children with acute gastrointestinal illness should consider testing rectal swabs when they need to rapidly identify enteropathogens and cannot immediately obtain a bulk stool sample, Stephen Freedman, MD, said at an annual scientific meeting on infectious diseases.
Among 1,519 children and adolescents with diarrhea, vomiting, or both symptoms, diagnostic yields of paired stool and rectal swab specimens were 76% and 68%, respectively, Dr. Freedman reported on behalf of the
Kappa values for concordance were 0.76 overall (95% confidence interval [CI], 0.71-0.80), .82 for viruses (0.79-0.86), and .74 for bacteria (0.68-0.80). A kappa value between 0.61 and 0.80 indicates “substantial” concordance between two results, while a value between 0.81 and 1.0 suggests “near perfect” concordance, explained Dr. Freedman of the University of Calgary (Alta.). In addition, 95% of health care providers and 82% of home caregivers considered rectal swabs easy to use, while 10% considered them unacceptable. “Recommendations against rectal swab use should be reconsidered,” he said.
Traditional testing of diarrheal bulk stool is highly specific, but burdensome and subject to various handling issues that can substantially delay diagnosis and outbreak detection, Dr. Freedman said at the combined annual meetings of the Infectious Diseases Society of America, the Society for Healthcare Epidemiology of America, the HIV Medicine Association, and the Pediatric Infectious Diseases Society.
“Flocked rectal swabs are used at the point of care and are quick and acceptable, but there are few precedents in the literature for their use in children or in patients with vomiting without diarrhea,” he said.
To help fill that gap, the researchers collected 1,147 stool specimens and 1,468 rectal swabs from patients under age 18 years who were seen at emergency departments in Calgary and Edmonton for diarrhea, vomiting, or both, with at least three episodes in the previous 24 hours. All of the patients had been ill for less than 7 days and had no detected psychiatric illness or neutropenia. Stool and rectal samples were evaluated three ways – by routine enteric bacterial culture, an in-house gastroenteric viral panel, and with the polymerase chain reaction-based Luminex xTAG Gastrointestinal Pathogen Panel. Swabs were taken by rotating them 360 degrees one time within the anus. Stool and swab specimens collected at home were stored at room temperature for less than 12 hours.
Among all paired specimens, 76% of stool samples and 68% of rectal swabs tested positive for at least one pathogen (P less than .0001). Thus, stool testing had about a 30% higher odds of detection than did swab testing in the same patient (OR, 1.3; 95% CI, 1.3-1.5). Odds ratios also favored stool testing in subgroups of patients with diarrhea (OR, 1.2; 95% CI, 1.1-1.4) or isolated vomiting (OR, 1.8; 95% CI, 1.5-2.1).
However, many stool specimens were never submitted, Dr. Freedman said. When the researchers assumed that these unsubmitted samples all tested negative, the diagnostic yield of stool samples fell to 57% and several odds ratios inverted in favor of rectal swabs. The study findings did not change when the researchers excluded positive results for Clostridium difficile in children younger than 2 years or when they restricted the analysis to paired specimens obtained within 24 hours.
The researchers are continuing to explore the diagnostic yield of rectal swab tests for multidrug-resistant pathogens, including those that are notifiable to public health departments, Dr. Freedman said.
Dr. Freedman disclosed ties to Copan Diagnostics, Luminex, and Alere.