Recurrent epidemics caused by a single strain of erythromycin-resistant Staphylococcus aureus. The importance of molecular epidemiology
N. A. Back, C. C. Linnemann Jr, M. A. Pfaller, J. L. Staneck and V. Morthland
Department of Infection Control, College of Medicine, University of Cincinnati, OH.
OBJECTIVE--To compare the accuracy of clinical epidemiologic findings with
results of molecular epidemiologic analysis in identifying the source of
recurrent epidemics of erythromycin-resistant Staphylococcus aureus (ERSA)
infections in a well-baby nursery. DESIGN--Epidemic investigations with
retrospective and prospective microbiological surveillance. Staphylococcus
aureus isolates were evaluated by plasmid analysis and genotyping.
SETTING--A well-baby nursery in a 700-bed university teaching hospital with
approximately 250 deliveries per month. PATIENTS--Newborn infants who
developed ERSA infections during 1990 and 1991. INTERVENTION--Traditional
infection control measures, including cohorting of infected infants and
hand washing, were implemented. Personnel were cultured for nasal carriage
of S aureus during both epidemics. Employees carrying ERSA were removed
from the nursery and treated with mupirocin. RESULTS--In the first
epidemic, 15 infants were infected with ERSA. A nursing assistant who cared
for most of the infants was found to be a carrier of ERSA. She was removed
from the nursery and the epidemic resolved. Fifteen months after the first
epidemic ended, an epidemic that involved 11 infants began. The attending
physician had a facial furuncle and was found to be a carrier of ERSA. The
physician was treated and the epidemic resolved. Plasmid and genotyping
showed the ERSA organisms from both epidemics were the same. The employee
implicated in the first epidemic did not have the epidemic strain, but the
physician who attended during both epidemics did. CONCLUSIONS--Traditional
epidemic investigations may lead to false conclusions that can only be
recognized with molecular epidemiologic techniques. For these techniques to
be useful in the control of outbreaks, plasmid analysis and/or genotyping
must be readily available.
