Background: Increasingly, clinical labs are migrating away from stool culture (cx) for bacterial pathogens toward newer assays to improve on sensitivity and specificity as well as turn-around-time. Our lab considered implementing a molecular assay that is capable of detecting Campylobacter, Shigella, Salmonella and Shiga-toxin producing organisms. However, this would mean that other potential pathogens like Aeromonas and Plesiomonas would go undetected. We sought to characterize the impact on patient (pt) management if clinicians were no longer aware of the presence of Aeromonas in the stool.
Methods: All pts with positive stool cx in the year 2014 were identified from the Kaiser Regional Reference Laboratory; only the first isolate per pt was included in the analysis. A retrospective chart review was performed.
Results: In the year 2014, Campylobacter was isolated from 853 pts, Salmonella in 370, Shigella in 116, Aeromonas in 114, and Plesiomonas in 5, the latter two represented 8% and 0.3% of the positive cx respectively. We examined the charts of 100/114 pts with Aeromonas. Species distribution included A caviae (41), A sobria (29), A hydrophila (20), A veronii (7) and Aeromonas sp (3). Other pathogens found concurrently included C difficile (8), Campylobacter (5), Salmonella (1) and rotavirus (1). In 20 episodes, empirical treatment was started as the cx was being sent. Of the remaining 80, 43 had become asymptomatic by the time the cx was back (38 not treated, 5 treated), 18 were treated without any documentation of the presence/absence of symptoms (sx), and 14 had other diagnoses made that accounted for their sx. Only 5 pts were noted to have persistent sx by the time the cx was available and were treated with resolution. Excluding the 18 pts who were treated without any documentation of sx, knowing that Aeromonas is present in the stool impacted the care of 5/82 (6%) pts.
Conclusion: Aeromonas was detected in <10% of bacterial stool cxs in our lab. For pts who did not receive an antibiotic with activity against Aeromonas, at least half became asx on their own. Of the evaluable cases, only 6% of pts potentially benefited from the additional information available with a stool cx. Molecular stool testing introduces some known unknowns for clinicians caring for pts with diarrhea but for an organism like Aeromonas, the clinical significance is minimal.