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Public health investigators linked two cases of multidrug-resistant bacterial infections in hospitalized patients to their most likely source -- a sink in the intensive care unit (ICU) room where both had stayed 4 months apart.

Each patient at the Idaho hospital in question had spent about a month in the ICU, had been on mechanical ventilation, and developed carbapenemase-producing carbapenem-resistant Pseudomonas aeruginosa (CP-CRPA) infections that turned up following serial sputum sampling, reported researchers led by Megan Cahill, PhD, of the Epidemic Intelligence Service at CDC and the Idaho Division of Public Health.

Isolates from the two patients revealed the same carbapenemase-producing gene that matched samples later taken from one of the ICU room sinks.

"Collaboration between healthcare facilities and public health agencies, including testing of CRPA isolates for carbapenemase genes and implementation of sink hygiene interventions, was critical in the identification of and response to this CP-CRPA cluster in a healthcare setting," the group wrote in the .

Both patients required prolonged mechanical ventilation (3 to 5 weeks) -- a risk factor for CRPA -- and had undergone routine serial sputum cultures to check for ventilator-associated infections or complications. In both cases, initial samples showed no signs of the multidrug-resistant infection, suggesting both had been hospital acquired.

The first case was identified in a middle-age woman on Sept. 17, 2021, after a fifth sputum sample collected via endotracheal tube aspiration turned up CRPA.

The second case was detected in a woman over 65 years on Jan. 25, 2022, on a third serial specimen sample. The patient was subsequently transferred to a long-term care facility but not put on contact precautions, as a notice never made it to the facility's infection preventionist. No evidence of person-to-person transmission at either facility was identified, however.

Both CP-CRPA isolates from the patients "had active-on-imipenem metallo-beta-lactamase (IMP) carbapenemase gene type 84 (bla_IMP-84) and were characterized as multilocus sequence type 235 (ST235)," according to results of whole genome sequencing performed at Utah Public Health Laboratory, which is part of CDC's Antibiotic Resistance Laboratory Network.

Between the two cases, 16 other patients had stayed in the same ICU room (median 3.5 days), but no other cases of CP-CRPA were detected. "It is possible that the shorter stays (≤12 days) or lack of mechanical ventilation reduced transmission risk," wrote Cahill and colleagues.

After the second case, the hospital closed the ICU room and on March 21-22, 2022, a team from the Idaho Division of Public Health came to collect environmental samples, including from sinks and toilets as "P. aeruginosa persists in biofilm, which is a collection of microorganisms that are adherent to one another and to a surface, such as pipes," the researchers noted.

That's when samples genetically similar to the two cases -- CP-CRPA ST235 with bla_IMP-84 -- were identified from a sink drain in the ICU.

After making the connection, the Idaho Division of Public Health Healthcare Associated Infections program, in consult with the CDC, made the following recommendations:

• Close the ICU room until the sink is disinfected "with a foam peracid mixture for drain biofilm disinfection against P. aeruginosa" and repeat weekly for all ICU room drains along with routine cleaning
• Add sink splash guards and introduce sink hygiene practices
• Collect specimens to look for CP-CRPA in the next 10 patients staying in the ICU room, or at least for 3 months
• Continue to submit CRPA isolates to the Idaho Bureau of Laboratories for carbapenemase gene identification
• After transfers, confirm that recommendations for contact precautions are received by infection preventionists

Adding the drain disinfectant to the sink cleaning routine appeared to do the trick in eliminating CP-CRPA, the researchers said, but they noted that the "optimal frequency of drain disinfection for disrupting CP-CRPA biofilm formation remains to be established."

Study limitations included that screening for infections was voluntary at the Idaho hospital and long-term care facility, so firm conclusions about the extent of transmission could not be made. Also, the mechanisms of transmission -- sink splashing onto patient care items, personnel, or visitors and then transferred to patients -- was not assessed.

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