This article details the appropriate microbiologic support that is critical to the successful investigation of nosocomial infection problems. The infection control team must have ready access to microbiologic data, and the laboratory should retain epidemiologically relevant bacterial isolates. Investigation of epidemics is facilitated by precise identification of bacteria and careful antibiotic susceptibility testing. In some situations, biotyping, serotyping, phage typing, bacteriocin typing, and other specialized techniques may be required. Plasmid analysis may be useful in the investigation of nosocomial infection problems caused by antibiotic-resistant bacteria.

Yersinia pestis, the etiologic agent of plague, is endemic in the western United States; 105 cases were reported between 1970 and 1979. Plague may manifest in one of three clinical forms: bubonic, septicemic, or pneumonic. Bubonic and septicemic plague represent relatively little risk for human-to-human transmission to contacts, although heavily infected secretions, such as drainage from a bubo, pose a theoretical risk, especially if they are aerosolized from a syringe during diagnostic aspirations. Pneumonic plague may be highly contagious to contacts and poses a greater risk. The Plague Branch, Center for Disease Control recommends that all patients with plague be placed in strict isolation for the first 48 hours of treatment because of the possibility that pneumonia may supervene. If it does not, wound and skin precautions are adequate for the duration of hospitalization. Untreated plague pneumonia is an epidemiologic emergency. All contacts must be identified promptly and those with face-to-face exposure should receive abortive antibiotic therapy. All contacts should be under surveillance, with twice-daily temperature checks, for seven days.

Sequential outbreaks of infection due to gentamicin-resistant Klebsiella pneumoniae (GRKP) types 30 and 19 occurred in the neonatal intensive care unit (NICU) at the Medical College of Virginia in 1977 and 1978. The extensive epidemiologic investigation carried out included a case-control study, careful review of aseptic technique, and cultures from nursery staff and environment. The gastrointestinal (GI) tracts of the patients were the reservoirs for GRKP, and the epidemic strain was transmitted by hands of personnel. The case-control study showed a significant relationship between acquisition of GRKP by patients and oropharyngeal and GI instrumentation, including use of bag resuscitation, oropharyngeal suctioning, and use of nasogastric feeding tubes. The findings of the case-control study were supported by observation of the patient care techniques practiced by NICU staff. Institution of control measures based on results of the epidemiologic investigation of the first outbreak rapidly brought the second outbreak under control, even though cohorting or use of routine isolation was not possible. Whereas GI colonization and hand transmission have been described previously in outbreaks of K. pneumoniae infections in NICUs, this study is the first to document the mode of inoculation of patients' GI tracts by contaminated hands of personnel.

The incidence and spectrum of resistance to gentamicin and tobramycin among gram-negative bacilli (GNB) isolated in a community hospital over a one-year period were studied. The overall incidence of resistance was 3.7%. Pseudomonads constituted almost half of the resistant organisms. The majority of resistant GNB was isolated from the respiratory and urinary tracts. Acquisition of resistance was correlated with both the total use of gentamicin in the hospital and recent treatment of individual patients with gentamicin plus tobramycin. The overall incidence of resistant isolates (3.7%) and the incidence of resistance for the enterobacteriaceae (1.9%) were lower than rates reported by comparable studies at several university or municipal hospitals.