A pseudo-outbreak of nosocomial infections associated with the introduction of an antibiotic management programme.

An abrupt and persistent 30% increase in the rate of nosocomial infections was detected at a university teaching hospital after a prolonged period with a relatively constant nosocomial infection rate. Demographic data, risk factors for nosocomial infection, features of reported cases of nosocomial infection, and policy and procedure changes were evaluated for the periods of 1 January 1997 to 30 April 1998 (endemic period) and 1 May to 31 December 1998 (epidemic period). An extensive outbreak investigation revealed no evidence of a true outbreak of nosocomial infection. The apparent outbreak involved all four major body sites, began during the same month that an antibiotic management programme was started, involved the same adult medical and surgical units where antibiotics were being controlled, and occurred months before any significant change in antibiotic usage. A greater proportion of nosocomial infection during the epidemic period was reported by the nosocomial infection surveillance nurses, based on a treating physician's diagnosis rather than on specific clinical criteria. In an attempt to justify existing antibiotic prescribing practices after the implementation of an antibiotic management programme, clinicians altered the threshold at which they documented the presence of nosocomial infection. This change in documentation produced a large pseudo-outbreak of nosocomial infection.