Most Staph aureus hospital transmission detected after readmission

A genomic surveillance study published in The Journal of Infectious Diseases found that most Staphylococcus aureus transmission events identified across two interconnected New York City hospitals became apparent only after patients were readmitted, limiting opportunities to recognize transmission during the index hospitalization.

Investigators conducted a 14-month observational cohort study among adults admitted to selected medicine, hematology/oncology, transplant, and intensive care units. All isolates obtained through admission screening underwent whole-genome sequencing. Among clinical isolates, investigators sequenced all methicillin-resistant S. aureus (MRSA) isolates, while methicillin-susceptible S. aureus (MSSA) sequencing was limited to blood-culture isolates. Approximately 4,800 isolates were analyzed. Investigators integrated genomic findings with patients’ temporal and spatial hospital exposures, identifying 361 transmission events that had not been detected through routine epidemiologic surveillance.

Colonization sampling was central to detecting transmission. In the real-time and delayed-detection analysis, 97% of evaluated events involved at least one colonization isolate, showing that clinical isolates alone captured little transmission. Repeated sampling also increased detection: restricting the analysis to each patient’s first isolate would have missed 33 of 146 direct transmission events, or 23%.

Transmission disproportionately involved MRSA, particularly the CC5 and CC8 lineages. Transmission probability increased with healthcare dependence across the evaluated strain groups, with the increase most pronounced for hospital-associated CC5. The CC5 relationship was steeper than that observed for MSSA but was not significantly different from CC8.

The authors said serial or discharge sampling may be needed to improve real-time detection. Because universal weekly or discharge screening would likely be impractical or cost-prohibitive, they proposed targeting surveillance according to patient- and strain-specific risk factors. Further studies are needed to determine whether targeted approaches can cost-effectively reduce MRSA transmission and its clinical consequences.

Source: Rabii KB, Takats C, Putzel G, et al. Sampling and host-strain interactions shape detection of Staphylococcus aureus transmission in hospitals. J Infect Dis. 2026. doi:10.1093/infdis/jiag361