The NNIS system was established in January 1970 and is currently the only nationwide source of information on nosocomial infections in the United States. This report examines surveillance among NNIS hospitals performing hospital-wide surveillance from 1980 to 1989. Patients were monitored for all nosocomial infections at all body sites. Standardized definitions for infection are provided to the participating hospitals but a variety of case-finding methods were used. Various methods for performing antimicrobial susceptibilities, including disk diffusion, macrobroth, and
microdilution are used, but each hospital must provide evidence of proficiency in the method being used. Data from each hospital are submitted monthly to the CDC. The percentage of coagulase-negative staphylococci
that were reported to be resistant to methicillin, oxacillin, or nafcillin (MRSE) was determined by estimating the mean percentage for 1989 for all hospitals that reported data. Hospitals that did not report susceptibility results for at least 20 coagulase-negative staphylococci in the year were ex- eluded from the analysis. Changes in percent of MRSE between two consecutive years were estimated using only the data from hospitals that reported to NNIS in both years.