Risk factors for nosocomial infection.

Studies of nosocomial infection are difficult to evaluate because of differences in the relative susceptibility of patients to the acquisition of such infections, the use of different methods of surveillance, and the frequent failure to distinguish between measurements of incidence and of prevalence. A standardized approach to these variables has been tested at a large municipal hospital. The systematic identification of potential risk factors for nosocomial infection allows the evaluation of the individual components of risk, valid epidemiologic comparisons between hospital populations, and a more accurate estimate of the potential cost-effectiveness of activities for the control of infection. The data indicate that it is feasible to calculate the relative risk of nosocomial infection for each patient, using basic criteria obtainable at the bedside, supplemented with other generally available information. The risk of infection must be calculated per day rather than per admission to separate the effect of long hospital stay from the effect of high daily risk. Certain underlying diseases, procedures, hospital services, and categories of age, sex, race, and urgency of admission were all found to be significant risk factors for nosocomial infection.