Molecular epidemiology of sequential nursery epidemics caused by multiresistant Klebsiella pneumoniae.

Multiresistant Klebsiella pneumoniae has been endemic among adult patients at Vanderbilt University Medical Center since 1973. Multiresistant K. pneumoniae was absent from pediatric wards until 1979, when it produced an epidemic in the intensive care nursery followed a year later by a second epidemic involving K. pneumoniae of the same serotype. The 105 megadalton (Md) conjugative resistance (R) plasmid (pCER7999) transferring multiple antibiotic resistance in the adult, endemic strain was found also in isolates from the first epidemic in the intensive care nursery. The mother of a child in the nursery harbored E. coli containing the same 105 Md R plasmid. The second epidemic also involved a 105 Md conjugative R plasmid, which, however, by molecular analysis was different from the first epidemic plasmid and also pCER7999. Thus, the second epidemic resulted from the introduction of a new, unrelated multiresistant K. pneumoniae strain. Contemporary hospital epidemiology often requires the application of molecular techniques for an understanding of nosocomial infections.