Detection of Aeromonas, Campylobacter and Salmonella using concurrent bacterial culture and commercial multiplex PCR, Sydney, Australia, 2023

BACKGROUND<i>Aeromonas, Campylobacter</i> and <i>Salmonella</i> species can cause gastrointestinal infections in humans. Information on the performance of detection methods is relevant to assess the impact of changes on surveillance.AIMWe aimed to assess detection of <i>Aeromonas</i>, <i>Campylobacter</i> and <i>Salmonella</i> by culture and Seegene multiplex real-time PCR in faecal samples from patients with gastrointestinal symptoms.METHODSIn 2023, all faecal samples submitted to a clinical microbiology laboratory in Sydney, Australia, were tested for <i>Aeromonas</i>, <i>Campylobacter</i> and <i>Salmonella</i> species by culture and Seegene PCR, both detecting at the genus level. The results were analysed descriptively and with binomial generalised linear model, quantile regression, censored regression model and Wald tests.RESULTSOf the 90,291 samples tested, more samples were positive with PCR than with culture for <i>Aeromonas</i> (PCR: 2.9%; culture: 0.5%) and <i>Campylobacter</i> (PCR: 4.2%; culture: 3.1%), but fewer for <i>Salmonella</i> species (PCR: 0.7%; culture: 0.8%). Of the culture-positive samples, 19.2% were negative for <i>Aeromonas</i> by PCR, 3.6% for <i>Campylobacter</i> and 23.0% for <i>Salmonella</i>. Of the PCR-positive samples, 81.9% were negative for <i>Aeromonas</i> by culture, 25.6% for <i>Campylobacter</i> and 14.2% for <i>Salmonella</i>. Quantification cycle (Cq) values were negatively associated with patient age for <i>Aeromonas,</i> indicating higher bacterial loads in older patients and positively associated with age for <i>Campylobacter</i>, indicating lower bacterial loads in older patients (p < 0.001). Also, Cq values were negatively associated with detection by culture and faecal calprotectin levels (p < 0.001).CONCLUSIONThese findings highlight the importance of pathogen- and method-specific interpretation of PCR and culture results in diagnostic testing and surveillance.