Diagnostic and Microbiological Impact of Multiplex Syndromic Testing for Acute Infectious Gastroenteritis in a Regional Laboratory Network: A Real-World Before–After Study

Acute infectious gastroenteritis (AIG) is caused by diverse bacterial and viral enteric pathogens with overlapping clinical presentations, limiting conventional pathogen-directed workflows. This retrospective before–after study evaluated the diagnostic, microbiological, operational, and economic impact of multiplex molecular syndromic testing for AIG within a regional hub-and-spoke laboratory network in Italy. Two 19-month periods were compared: a pre-implementation period based on conventional diagnostics and a post-implementation period using multiplex syndromic panels as first-line tests. Diagnostic investigations totalled 25,574 before and 24,509 after implementation. Overall test positivity increased from 5.43% to 11.59% (p < 0.001), with significant increases for bacterial and viral targets. Pathogen detection events increased from 1388 to 2839, including broader detection of Campylobacter spp., Shigella spp./enteroinvasive Escherichia coli (EIEC), Yersinia enterocolitica, Aeromonas spp., Astrovirus, Sapovirus, and Norovirus genogroups. Mean turnaround time decreased from 63 to 47 h from sample collection and from 56 to 41 h from laboratory check-in. Although direct diagnostic costs increased moderately, total laboratory costs decreased when personnel costs were included, and cost per diagnostic detection declined from €233.80 to €120.86. Multiplex syndromic testing improved microbiological detection, diagnostic efficiency, turnaround time, and laboratory organisation in routine AIG diagnosis.