# P-149. Increased detection of Clostridioides difficile in adults’ stool specimens with multiplex infectious diarrhea panel nucleic-acid amplification testing

## TL;DR

A study in British Columbia found that using a new multiplex test for intestinal pathogens led to more positive C. difficile results, which could cause misinterpretation of outbreaks and over-treatment.

## Contribution

The study shows how multiplex testing increases C. difficile detection, potentially leading to pseudo-outbreaks and overprescription.

## Key findings

- C. difficile positivity rate decreased from 6.73% to 5.02% after implementing multiplex testing.
- The number of positive C. difficile results nearly doubled after the new test was introduced.
- The increase in positive results may mislead epidemiologists and lead to overprescription.

## Abstract

Since 2022, diagnostic laboratories in British Columbia (BC), Canada, have been advised to replace traditional bacterial, viral and parasitic intestinal pathogen testing with multiplex infectious diarrhea panel nucleic-acid amplification testing (IDP-NAAT), which contains a minimum of 14 common pathogens, including C. difficile. However, multiplex testing can lead to false positive targets which are not even in the clinicians’ differentials. The Infectious Diseases Society of America Guidelines (2017) for C. difficile infection have specific indications for testing rather than routine testing for all patients with diarrhea. The current study investigated whether multiplex IDP-NAAT would lead to higher prevalence of positive C. difficile results, signaling a pseudo-outbreak.

LifeLabs BC microbiology laboratories, connected with 129 collection centres in communities in the province, provided the laboratory data on C. difficile results from adult patients (age >18 years). An audit was conducted from September 2022 to August 2023, one year prior to implementation of IDP-NAAT in LifeLabs, when C. difficile NAAT followed with antigen testing was used, per request only. Another audit was conducted from October 2023 to September 2024, one year after the implementation of multiplex IDP-NAAT followed with C. difficile antigen testing for confirmation. Chi-square with Yates correction was used to compare the change.

Prior to implementation of IDP-NAAT, 1475 of 21912 patient’s stool specimens (6.73%) submitted for testing was positive for C. difficile. After the implementation, 2838 of 56590 patients’ stool specimens (5.02%; p < 0.05 vs. prior) submitted for testing was positive for C. difficile.

Although the positivity rate of C. difficile decreased, the number of positive C. difficile results increased almost twice after the implementation of IDP. This increase could mislead epidemiologists to suspect an outbreak and clinicians to overprescribe for C. difficile colonization rather than infection. More communications and educations may be warranted to remind clinicians that positive C. difficile NAAT results are not always indicative of infection due to implementation of multiplex testing on all stool specimens.

All Authors: No reported disclosures