Pseudo-outbreak of Carbapenemase producing Enterobacteraciae (CRE) in a low prevalence acute-care hospital
Methods: A patient was admitted from another facility with CRE urinary tract infection. A second patient on the same unit grew CRE from urine with an identical resistance antibiogram. The second patient had no risk factors for CRE. An outbreak investigation was initiated. A prevalence survey for CRE was performed on all patients on the unit using rectal swabs. Staff were educated in order to answer any patient questions or concerns. Swabs were sent to Quest Laboratories for plating on a new CHROMagar CRE plate.
Results: All 22 patients on the inpatient unit underwent screening including the two patients with CRE initially identified from urine clinical cultures. No patients refused screening. Presumptive positive results were identified by growth on the CRE CHROMagar for 3 patients, as well as one of two patients with initially positive urine cultures. The three additional patients identified by screening were notified of these results and placed on Contact Precautions. However, the final identification of these 3 isolates by Vitek found them to be Stenotrophomonas and Pseudomonas species, and not CRE despite growth on the CRE plate. CRE designations were removed and patients re-educated with the updated results. The second patient had a repeat urine culture that did not grow CRE, despite no intervening treatment. In summary, of 5 patients who were thought to have CRE in this pseudo-outbreak, only one patient with CRE on admission was finally identified as positive.
Conclusion: Having a high index of suspicion for CRE in low prevalence settings carries a risk of false positive results. New CHROMagar methods of CRE detection must be interpreted carefully. As healthcare centers across the country develop strategies for identification and control of CRE, potential outbreaks will need to be approached with caution to minimize the impact on misidentified patients and to allay alarm among staff.
M. C. Roghmann, None
D. Morgan, None