Percentage of culture confirmation and melting curve analysis reveals false-positive Campylobacter detection in a molecular syndromic panel

Abstract

Surveillance of enteric organisms can identify outbreaks and support control measures. The BIOFIRE FilmArray Gastrointestinal Panel (FilmArray GI) is the most common culture-independent diagnostic test (CIDT) used in Wisconsin to diagnose enteric infections. State clinical laboratories have raised concerns about inaccurate Campylobacter detection with the FilmArray GI. The Wisconsin State Laboratory of Hygiene (WSLH) evaluated the percentage of positivity and culture confirmations stratified by CIDT for Campylobacter, Salmonella, and STEC from 2018 to 2024. We further analyzed the transport time of Campylobacter specimens and the melt curves of specimens that tested positive by FilmArray GI. Campylobacter, Salmonella, and STEC specimens tested on the FilmArray GI had increases in percentage of positivity compared to those tested on other CIDTs. Salmonella and STEC specimens positive by FilmArray GI, compared to other CIDTs, had no significant culture confirmation differences. However, Campylobacter specimens positive by FilmArray GI had significantly lower culture confirmations than positive specimens from other CIDTs (62% vs. 78%; P < 0.05). Campylobacter culture confirmations were lower for FilmArray GI specimens, compared to other CIDTs, regardless of how many days the specimen spent in transport in 2023. Additionally, we found atypical melt curves among specimens positive by FilmArray GI with cultures that did not grow Campylobacter. Taken together, the higher percentage of positivity, the lower percentage of culture confirmation, and the atypical melt curves suggest that the FilmArray GI might yield false-positive Campylobacter results. These findings emphasize the importance of public health surveillance to identify potential issues with commercially available diagnostic tests.