Public health investigators have identified a link between two cases of multidrug-resistant bacterial infections in hospitalized patients and a sink in the intensive care unit (ICU) room where both patients had stayed. The patients had spent approximately one month in the ICU, were on mechanical ventilation, and developed carbapenemase-producing carbapenem-resistant Pseudomonas aeruginosa (CP-CRPA) infections. The isolates from the patients were found to have the same carbapenemase-producing gene as samples taken from one of the ICU room sinks. This article examines the investigation and its findings, highlighting the importance of collaboration between healthcare facilities and public health agencies in response to such clusters.
The first case of CP-CRPA infection was identified in a middle-aged woman on September 17, 2021, after a sputum sample collected via endotracheal tube aspiration turned up positive for CRPA. The second case was detected in a woman over 65 years on January 25, 2022, on a third serial specimen sample. The patients required prolonged mechanical ventilation, which is a known risk factor for CRPA. Routine serial sputum cultures were performed to check for ventilator-associated infections or complications. Both initial samples showed no signs of the multidrug-resistant infection, suggesting that both cases were hospital-acquired.
Genetic sequencing of the CP-CRPA isolates from the two patients revealed an active-on-imipenem metallo-beta-lactamase (IMP) carbapenemase gene type 84 (blaIMP-84) and a multilocus sequence type 235 (ST235) classification. Whole genome sequencing performed at Utah Public Health Laboratory confirmed these findings. While 16 other patients had stayed in the same ICU room, no additional cases of CP-CRPA were detected. The researchers hypothesized that the shorter stays or lack of mechanical ventilation in these patients may have reduced the transmission risk. However, the exact mechanisms of transmission were not assessed in this investigation.
After the second case of CP-CRPA infection, the ICU room was closed, and a team from the Idaho Division of Public Health collected environmental samples, including from sinks and toilets. Sink drains were identified as the source of genetically similar CP-CRPA isolates, specifically CP-CRPA ST235 with blaIMP-84. Based on these findings, the Idaho Division of Public Health Healthcare Associated Infections program, in consultation with the CDC, made several recommendations to prevent further transmission:
- Close the ICU room until sink disinfection is completed using an EPA-registered peracid mixture for biofilm disinfection against P. aeruginosa.
- Implement routine weekly sink disinfection for all ICU room drains.
- Add sink splash guards and introduce sink hygiene practices.
- Collect specimens from the next 10 patients in the ICU room to check for CP-CRPA infections.
- Continue to submit CRPA isolates for carbapenemase gene identification.
- Ensure recommendations for contact precautions are received by infection preventionists after patient transfers.
The addition of drain disinfectant to the sink cleaning routine effectively eliminated CP-CRPA in this case. However, the researchers acknowledged that the optimal frequency of drain disinfection for disrupting CP-CRPA biofilm formation remains to be established.
It is important to note the limitations of this study. The screening for infections was voluntary at the Idaho hospital and long-term care facility, which may have impacted the extent of transmission observed. Furthermore, the exact mechanisms of transmission, such as sink splashing onto patient care items or personnel and subsequent transfer to patients, were not assessed. Despite these limitations, the investigation highlights the significance of collaboration between healthcare facilities and public health agencies in identifying and responding to clusters of multidrug-resistant infections.
The link between the multidrug-resistant infections in the ICU patients and the sink highlights the need for effective sink hygiene practices in healthcare settings. Sink drains, where biofilm can persist, can serve as reservoirs for multidrug-resistant bacteria. Disinfection of sinks and implementing sink hygiene practices, along with routine cleaning and contact precautions, are essential in preventing the transmission of these infections. Future research should focus on establishing optimal disinfection protocols to disrupt biofilm formation and further understanding the mechanisms of transmission in healthcare settings.