Discussion

We report a hospital outbreak of 21 cases of R. mannitolilytica bloodstream infection traced to contaminated pre-filled 10 mL 0.9% sodium chloride vials in immunocompromised patients with central venous access. Laboratory-driven cluster detection, immediate IPC notification, and a coordinated multidisciplinary response—including microbiology, infectious diseases, IPC, pharmacy, nursing, and hospital administration—enabled identification and removal of the contaminated product within 24 hours of cluster recognition.

Despite hospitalwide distribution of the implicated product, clinical infections occurred almost exclusively in immunocompromised patients with central catheters, consistent with combined host susceptibility and intravascular biofilm-mediated pathogenesis. ^{Reference Ryan and Adley20–Reference Nurjadi, Boutin, Schmidt, Ahmels and Hasche22}

R. pickettii was co-isolated in 4 of 21 patients, in each case only after 48 hours of incubation and always together with R. mannitolilytica. R. pickettii was not recovered from the implicated saline vials or from any other product or environmental sample, and the outbreak clone defined by PFGE was R. mannitolilytica. The two species commonly co-occur in water-based reservoirs, and low-level co-contamination or recovery of a slow-growing commensal cannot be excluded; however, the clinical significance of the co-isolates is uncertain, and they did not alter management because all isolates were susceptible to trimethoprim–sulfamethoxazole.

A notable feature of this investigation was the speed of source identification. Nonetheless, seven bacteremias occurred within the first 48 hours before the cluster was acted upon, and saline-associated Ralstonia outbreaks had already been reported in several jurisdictions. Because Ralstonia is a rare and characteristically product-associated pathogen, even a single case of Ralstonia spp. bacteremia—particularly in a patient receiving sterile infusates—should prompt immediate investigation and a low threshold for suspending potentially implicated medications or solutions pending results. Microbiology recognition of an unusual same-day cluster, immediate IPC engagement, and protective suspension of the suspected lot before microbiological confirmation appear to have limited outbreak size and severity.

Several late-onset infections occurred more than one week after product withdrawal, all in immunocompromised patients with intravascular devices. Both relapses occurred after initial line retention and resolved only after device removal—consistent with, though, given the small numbers, not proof of, an important role for catheter removal in catheter-associated Ralstonia infection.

To our knowledge, this is the first reported Ralstonia outbreak from Oman. The investigation reinforces several operational lessons. First, introduction of a new pharmaceutical product—particularly a single-use sterile flush in widespread use across high-risk units—warrants heightened postintroduction surveillance; the implicated product, a newly introduced brand of 0.9% saline vials, had been in clinical use for only 5 days before the cluster was detected. Following this event, the hospital has implemented postintroduction surveillance with enhanced monitoring and sentinel culturing for newly introduced sterile pharmaceutical products and lots in high-risk units. Second, decisive temporary suspension of suspected products before microbiological confirmation is a high-value, low-cost intervention, with reintroduction once the product is exonerated. Where a suspected product is the sole available lot or a single-source item that cannot be withdrawn without disrupting essential care, we recommend a graded response rather than outright suspension: substituting an alternative formulation where one exists, restricting use to clinical necessity, reinforcing aseptic preparation, quarantining and sequestering the implicated lot for priority testing, and escalating immediately to the supplier and regulator to arrange expedited replacement stock or recall. Third, molecular typing (PFGE here; whole-genome sequencing where available) provides confirmatory evidence of clonality that strengthens the case for product recall and informs cross-border alerts for internationally distributed products. ^{Reference Saunders, Weaver and Stretch2}

This investigation has limitations. PFGE was performed on 18 of 21 clinical isolates and on the single culture-positive product sample; although the concordant epidemiological, antibiogram, and molecular findings strongly support the implicated source, not every potential environmental sample underwent molecular comparison. Whole-genome sequencing was not available at the time of the investigation; consequently, while PFGE confirmed clonality within our outbreak, we could not determine whether our strain is related to those implicated in saline-associated Ralstonia outbreaks in other jurisdictions or exclude a shared, internationally distributed source at higher resolution. Finally, our experience reflects a single tertiary-care center, and delayed detection may occur in institutions with different surveillance systems or smaller microbiology capacity.

In conclusion, pre-filled saline vials can serve as a source of clonal R. mannitolilytica BSI outbreaks among immunocompromised patients. Robust laboratory surveillance, immediate multidisciplinary engagement, decisive product suspension, and timely catheter removal enabled containment within 24 hours and prevented outbreak-related mortality. Vigilance after introduction of new pharmaceutical products, a low threshold for investigating even single cases, and inter-institutional communication are essential to limit similar events.