Patient-Hospital Bacteria Transmission a Two-Way Street

Bridget M. Kuehn

June 15, 2017

From the moment a patient sets foot in a hospital, the communities of bacteria on their body are shaped by those of their caregivers and their room. A patient's bacteria also quickly begin to shift the microbial flora of their rooms.

Simon Lax, a doctoral student of ecology and evolution at the University of Chicago, Illinois, and colleagues report their findings in an article published May 24 in Science Translational Medicine. The study provides the first comprehensive look at the complex ecology of microbes in a newly opened hospital. The results lay the groundwork for more study of how a hospital's microbial ecology affects patient health, and may help scientists better understand how these ecosystems may contribute to hospital-acquired infections.

In the study, a newly constructed hospital, the University of Chicago's Center for Care and Discovery, was sampled for bacteria starting 2 months before the facility opened in February 2013 and for a year after opening day. More than 6500 microbial samples were taken from 10 patient rooms and two nurse stations on two floors to track changes in the microbial communities on hospital surfaces. In addition, samples from patients in those rooms and their nurses were collected to determine how humans' microbial flora contributed.

The samples were genetically sequenced to allow the researchers to identify genetic variations in bacteria strains and to track their spread. Hospital staff disinfected all patient rooms daily with a solution of quaternary ammonium, and on discharge with bleach solution.

The abundance of common skin-dwelling bacteria such as Corynebacterium, Staphylococcus, and Streptococcus quickly increased on hospital surfaces such as the floors and nurse stations after the facility opened. The prevalence of bacteria including Acinetobacter and Pseudomonas that were common in the building before opening decreased once patients and staff moved in.

Patients initially acquired new bacterial strains that were present in their room before their arrival. But over time, the microbial communities on surfaces in the patient's room, particularly the bedrails, became more similar to the patient's own flora. Surprisingly, treatments such as chemotherapy, antibiotics, or surgery had only a weak or statistically insignificant effect on patients' skin microbiota. But how much patients were able to get around did affect the mix of their skin microbes, likely because more mobile patients were exposed to a broader array of bacteria.

Hospital surfaces were more likely to be home to antibiotic-resistant bacteria than patients' skin. In addition, nurses were more likely to pass bacteria strains from their own skin to their patients than vice versa.

"When patients enter a hospital, they arrive with complex and dynamic microbial assemblages that will be shaped by the treatment they receive and by the interactions they have with staff and with the building itself," the authors say.

The researchers caution that because the study was observational and did not test any interventions, its immediate clinical implications are limited. However, they suggest that future studies may lead to infection-reducing hospital interventions.

"As the influence of human microbial ecology on patient care and recovery in the hospital environment becomes better understood, being able to reinforce beneficial microbial interactions and mitigate harmful ones throughout the course of hospitalization will become paramount," the authors explain.

The authors have disclosed no relevant financial relationships.

Sci Transl Med. 2017;9:eaah6500. Abstract

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