Hospitals: Helpful Humidity

• Share

Ever since Lord Lister rigged up an apparatus to squirt a curtain spray of phenol around his operating table, surgeons have worried about bacteria flying through the air and into a patient's wound. Trouble is, there has been next to no information about how many germs, of what kinds, are in the operating room's air, or—more importantly—about where the bugs come from.

A research team headed by Surgeon Harvey R. Bernard at Barnes Hospital in St. Louis has spent years seeking answers to these fundamental questions. One clear conclusion: surgeons, nurses and patients themselves carry most of the dangerous germs, especially the resistant strains of staphylococci, into the operating theater. Relatively few appear in the air, and it makes little difference whether the air is continually drawn fresh from outdoors, or whether it is recirculated after filtering.

It is the humidity, Dr. Bernard's team reports in Surgery, that contributes most to the safety of the air. Fortunately, what is comfortable for people seems to be deadly for many bacteria, notably staph. The germs thrive in dry air (relative humidity less than 35%), and in moist air (65% or over). They languish and die in the middle zone. So the St. Louis researchers recommend keeping the humidity control on operating-room air conditioners at the 50% evel—a setting that is best for operat-ng personnel, worst for germs, and moist enough to minimize the ever-present danger of anesthetic explosions from static electricity.