NOSOCOMIAL INFECTIONS

A nosocomial infection is an infection that is acquired in a hospital. More precisely, the Centers for Disease Control in Atlanta, Georgia, defines a nosocomial infection as a localized infection or one that is widely spread throughout the body that results from an adverse reaction to an infectious microorganism or toxin that was not present at the time of admission to the hospital.

The term nosocomial infection derives from the nosos, which is the Greek word for disease.

Nosocomial infections have been a part of hospital care as long as there have been hospitals. The connection between the high death rate of hospitalized patients and the exposure of patients to infectious microorganisms was first made in the mid-nineteenth century. Hungarian physician Ignaz Semmelweis (1818–1865) noted the high rate of death from puerperal fever in women who delivered babies at the Vienna General Hospital. Moreover, the high death rate was confined to a ward at which medical residents were present. Another ward, staffed only by midwives who did not interact with other areas of the hospital, had a much lower death rate. When the residents were made to wash their hands in a disinfectant solution prior to entering the ward, the death rate declined dramatically.

At about the same time, the British surgeon Joseph Lister (1827–1912) also recognized the importance of hygienic conditions in the operating theatre. His use of phenolic solutions as sprays over surgical wounds helped lessen the spread of microorganisms resident in the hospital to the patient. Lister also required surgeons to wear rubber gloves and freshly laundered operating gowns for surgery. He recognized that infections could be transferred from the surgeon to the patient. Lister's actions spurred a series of steps over the next century, which has culminated in today's observance of sterile or near-sterile conditions in the operating theatre.

Despite these improvements in hospital hygienic practices, the chance of acquiring a nosocomial infection still approaches about 10%. Certain hospital situations are even riskier. For example, the chance of acquiring a urinary tract infection increases by 10% for each day a patient is equipped with a urinary catheter. The catheter provides a ready route for the movement of bacteria from the outside environment to the urinary tract.

The most common microbiological cause of nosocomial infection is bacteria. The microbes often include both Gramnegative and Gram-positive bacteria. Of the Gram-negative bacteria, Escherichia coli, Proteus mirabilis, and other members of the family known as Enterobacteriacaea are predominant. These bacteria are residents of the intestinal tract. They are spread via fecal contamination of people, instruments or other surfaces. Other Gram-negative bacteria of consequence include members of the genera Pseudomonas and Acinetobacter.

Gram-positive bacteria, especially Staphylococcus aureus, frequently cause infections of wounds. This bacterium is part of the normal flora on the surface of the skin, and so can readily gain access to a wound or surgical incision.

One obvious cause of nosocomial infections is the state of the people who require the services of a hospital. Often people are ill with ailments that adversely affect the ability of their immune systems to recognize or combat infections. These people are more vulnerable to disease than they would otherwise be. A hospital is a place where, by its nature, infectious microorganisms are encountered more often than in other environments, such as the home or workplace. Simply by being in a hospital, a person is exposed to potentially diseasecausing microorganisms.

A compounding factor, and one that is the cause of many nosocomial infections, is the developing resistance of bacteria to a number of antibiotics in common use in hospitals. For example, strains of Staphylococcus aureus that are resistant to all but a few conventional antibiotics are encountered in hospitals so frequently as to be almost routine. Indeed, many hospitals now have contingency plans to deal with outbreaks of these infections, which involve the isolation of patients, disinfection of affected wards, and monitoring of other areas of the hospital for the bacteria. As another example, a type of bacteria known as enterococci has developed resistance to virtually all antibiotics available. Ominously, the genetic determinant for the multiple antibiotic resistance in enterococci has been transferred to Staphylococcus aureus in the laboratory setting. Were such genetic transfer to occur in the hospital setting, conventional antibiotic therapy for Staphylococcus aureus infections would become virtually impossible.