Molecular epidemiology of Staphylococcus epidermidis in a neonatal intensive care unit over a three-year period.

Coagulase-negative staphylococci, especially Staphylococcus epidermidis, are increasingly important nosocomial pathogens, particularly in critically ill neonates. A 3-year prospective surveillance of nosocomial infections in a neonatal intensive care unit (NICU) was performed by traditional epidemiologic methods as well as molecular typing of microorganisms. The aims of the study were (i) to quantify the impact of S. epidermidis on NICU-acquired infections, (ii) to establish if these infections are caused by endemic clones or by incidentally occurring bacterial strains of this ubiquitous species, (iii) to evaluate the use of different methods for the epidemiologic typing of the isolates, and (iv) to characterize the occurrence and the spread of staphylococci with decreased glycopeptide susceptibility. Results confirmed that S. epidermidis is one of the leading causes of NICU-acquired infections and that the reduced glycopeptide susceptibility, if investigated by appropriate detection methods such as population analysis, is more common than is currently realized. Typing of isolates, which can be performed effectively through molecular techniques such as pulsed-field gel electrophoresis but not through antibiograms, showed that many of these infections are due to clonal dissemination and, thus, are potentially preventable by strict adherence to recommended infection control practices and the implementation of programs aimed toward the reduction of the unnecessary use of antibiotics. These strategies are also likely to have a significant impact on the frequency of the reduced susceptibility of staphylococci to glycopeptides, since this phenomenon appears to be determined either by more resistant clones transmitted from patient to patient or, to a lesser extent, by strains that become more resistant as a result of antibiotic pressure.

Unusual genetic heterogeneity of Acinetobacter baumannii isolates in a university hospital in Italy.

BACKGROUND: Acinetobacter baumannii has become an increasingly important nosocomial pathogen, particularly in intensive care units (ICUs). The aim of this investigation was to study the molecular epidemiology of A baumanii in a university hospital in Italy. METHODS: All A baumanii isolates were collected and typed with phenotypic and genotypic methods during a 7-month period. A 1-year prospective surveillance of ICU-acquired infections was performed by using the National Nosocomial Infections Surveillance methodology. RESULTS: A baumanni accounted for 28.4% of all infections and 46.7% of all pneumonia acquired in the ICU, with a nosocomial infection rate of 12.4% or 8 infections per 1000 patient-days. Risk factors for A baumannii acquisition in the ICU were mechanical ventilation and previous use of broad-spectrum antibiotics, whereas administration of carbapenems showed a significant protective effect. Pulsed-field gel electrophoresis of genomic Apa I digests identified at least 5 outbreaks in the ICU caused by 5 different clones, one replacing the other in a well-defined temporal order. CONCLUSIONS: Whereas the sequential temporal cluster of epidemic clones in the ICU is intriguing and requires further research, the clear evidence of cross-contamination of A baumannii isolates involved with infections in the ICU demands extensive preventive efforts.

Molecular epidemiology as an effective tool in the surveillance of infections in the neonatal intensive care unit.

OBJECTIVES: nosocomial infections result in considerable morbidity and mortality in Neonatal Intensive Care Units (NICUs). The aim of this study was to investigate the usefulness of the molecular epidemiology approach in the surveillance and control of infections in the NICU. METHODS: a 1-year prospective surveillance of nosocomial infections in a NICU was performed using traditional epidemiological methods as well as molecular typing of micro-organisms. RESULTS: the nosocomial infection rate among the 343 newborns was 24.8%. The risk of infection was associated with low birth weight, prolonged length of stay, empiric antibiotic treatment and nasopharyngeal colonization. Four pathogens (Klebsiella pneumoniae, methicillin-resistant Staphylococcus aureus (MRSA), methicillin-resistant Staphylococcus epidermidis (MRSE) and methicillin-sensitive Staphylococcus aureus (MSSA) were responsible for more than 80% of the infections. Extended-spectrum beta-lactamase-producing (ESBL) K. pneumoniae and MRSA infections constituted outbreaks caused by a single clone, whereas MRSE and MSSA infections did not represent outbreaks but rather a series of sporadic infections caused by different strains. CONCLUSIONS: molecular epidemiology techniques are powerful tools that can elucidate modes of spread and reservoirs of infection in the NICU and identify effective measures to control epidemic or endemic situations.