Plumbing Contamination Linked with Cluster of Infections from Rare Sphingomona Species

A new study published in the New England Journal of Medicine details a genomic and epidemiologic investigation into a small outbreak of multidrug-resistant Sphingomonas koreensis infections that occurred at a National Institutes of Health (NIH) Clinical Center, which investigators concluded was linked with contamination in the facility’s plumbing system.

Health care-associated infection (HAI) rates are down overall in the United States but remain a problem in health care settings. In 2015 there were an estimated 687,000 HAIs in US acute care hospitals, and 72,000 hospital patients with HAIs died during their hospitalizations. Although surgical site infections, pneumonia, and Clostridium difficile infections account for most HAIs, the NEJM study detailed a cluster of infections caused by waterborne Sphingomonas species, including S koreensis, an uncommon gram-negative bacterium that was first documented as a human pathogen in a 2015 study.

According to the report by NIH investigators, 6 patients at the NIH Clinical Center in Bethesda, Maryland, became infected with Sphingomonas species during a 6-month period in 2016. The investigators conducted whole genome sequencing on the isolates from patients infected with Sphingomonas and tested water samples from the faucets in their hospital rooms.

Sequencing identified 4 samples as S koreensis, 1 as S yanoikuyae, and 1 as S trueperi. The S koreensis isolates had a strong degree of genetic similarity (99.92% average nucleotide identity), suggesting they belonged to the same clonal strain. Additionally, the S koreensis isolates exhibited resistance to multiple classes of antibiotics including aminoglycosides, beta-lactams, and fluoroquinolones.

After conducting passive surveillance going back to 2006, soon after the facility was built and opened, investigators discovered S koreensis clinical isolates in a total of 12 patients at the hospital, with the 8 older isolates also showing genetic similarity (>99.98% average nucleotide identity) to the newer isolates.

The investigators collected 55 S koreensis isolates in water samples from facility faucets, which were also strongly genetically similar to the isolates in infected patients (>99.7% average nucleotide identity) and genetically distinct when compared with isolate samples from other facilities.

The NIH Clinical Center has seen no new S koreensis infections since investigating the plumbing and faucets in the facility and taking steps to augment free chlorine concentrations in the water and adjusting the hot water temperature in December 2016.

“Our results suggest that a single S koreensis strain entered the water system soon after construction of the new NIH Clinical Center hospital building in 2004,” investigators wrote. “Previous studies have underscored the threat that in-room sinks may pose to patients, from both potable water and splashback from the drain. The steps taken in this study to prevent further S koreensis infections within the NIH Clinical Center are applicable to many opportunistic waterborne pathogens.”

In an interview with Contagion®, study co-author and NIH Clinical Center hospital epidemiologist Tara Palmore, MD, said that the investigators are aware of other hospitals with the same bacteria that have not yet published or publicized their experience, and the team has shared their knowledge with institutions with suspected Sphingomonas in the building.

“As with all research published at the NIH Clinical Center, we hope that our findings will raise awareness in the medical community, particularly hospitals that serve highly immunocompromised patients such as transplant recipients, to the possibility that these bacteria can be in their water fixtures and can cause sporadic infections in patients,” said Dr. Palmore. “We also wanted to share the genomic analysis, which was of scientific interest and importance in our investigation. If hospitals are aware of this potential, their own water management committees may use their resources to detect or prevent plumbing colonization and patient infections with similar bacteria.”