The investigators swabbed each patient’s hand, nostril and armpit, as well as the surfaces patients may have touched, such as bedrails or faucet handles. They collected additional room samples from multiple surfaces, including the floor and the air filter. Each room was cleaned daily, with a more extensive cleaning after each patient’s discharge.
The researchers also gathered samples from each unit’s nursing staff, swabbing their hands, gloves, shoes, nursing station countertops, pagers, shirts, chairs, computers, landlines and cell phones.
The most obvious change came when the hospital opened, which followed extensive cleaning efforts. Bacterial organisms such as Acinetobacter and Pseudomonas, abundant during construction and pre-opening preparations, were quickly replaced by human skin-associated microbes such as Corynebacterium, Staphylococcus and Streptococcus, brought in by patients.
“Before it opened, the hospital had a relatively low diversity of bacteria,” Gilbert said. “But as soon as it was populated with patients, doctors and nurses, the bacteria from their skin took over.”
A second, and ongoing, set of changes followed each patient’s hospital admission. On a patient’s first day in the hospital, microbes tended to move from surfaces in the patient’s room—bedrails, countertops, faucet handles—to the patient. But by the next and every subsequent day, the preponderance of microbes moved in the other direction, from the patient to the room, steadily adding to the microbial diversity of the surfaces in the room.
“By the second day of their stay,” Gilbert said, “the route of microbial transmission was reversed. Within 24 hours, the patient’s microbiome takes over the hospital space.”
There were two unanticipated findings. First, when the heat and humidity increased during the summer, staff members shared more bacteria with each other. Second, when they measured the impact of treatments—such as antibiotics prior to or during admission, chemotherapy during admission, surgery, or admission to the hospital though the emergency department—the impact was minimal.
“We consistently found that antibiotics given intravenously or by mouth had almost no impact on the skin microbiome,” Gilbert said. “But when a patient received a topical antibiotic, then, as expected, it wiped out the skin microbes.”
Samples from the rooms of 92 patients who had longer hospital stays, measured in months, revealed a trend. Some potentially harmful bacteria, such as Staphylococcus aureus and Staphylococcus epidermidis, faced with continual selective pressure, managed to acquire genes that could boost antibiotic resistance and promote host infection.
“This requires further study,” Gilbert said, “but if it proves to be true then these genetic changes could affect the bacteria’s ability to invade tissue or to escape standard treatments.”
The study, published May 24 in Science Translational Medicine, “demonstrates the extent to which the microbial ecology of patient skin and of hospital surfaces are intertwined and may provide context to future studies of the transmission of hospital-acquired infections,” the authors conclude.
—This article first appeared on the Science Life website