Prevalence of Staphylococcus aureus introduced into intensive care units of a University Hospital

Staphylococcus aureus is one of the principal human pathogens that colonize healthy individuals in the community in general, and it is responsible for severe infections in hospitalized patients. Due to an increase in the prevalence of strains of methicillin-resistant S. aureus (MRSA), combating these microorganisms has become increasingly difficult. A descriptive study was carried out on 231 patients in intensive care at the Oswaldo Cruz University Hospital (HUOC) in Recife, Brazil between January and April 2003 to determine the prevalence of S. aureus and MRSA and to evaluate risk factors for colonization by these bacteria when introduced into Intensive Care Units (ICUs). Body secretions were collected from the nostrils, axillary and perineal regions, and from broken skin lesions, of all patients during the first 48 hours following admission to the ICU. Samples were inoculated into blood agar and mannitol-salt-agar culture medium and identified by Gram staining, and by coagulase, DNAse and agglutination (Slidex Staph Test) tests. Growth in Mueller-Hinton agar with 4% sodium chloride and 6 mg/L oxacillin was used to identify MRSA. In addition, the latex agglutination test was performed to identify penicillin-binding protein, PBP 2A. The prevalence of S. aureus and MRSA was 87/231 (37.7%) and 30/231 (12.98%), respectively. There was no association between any risk factor studied (age, sex, origin of the patient--whether hospital or community, previous hospitalization, use of current or previous antibiotic therapy, corticotherapy and/or immunotherapy, reason for hospitalization and place of hospitalization) and the presence of S. aureus. However, a significant association was established between previous hospitalization and the presence of MRSA (RR:1.85; CI:1.00-3.41; p=0.041). The nostrils were the principal site of colonization by both S. aureus (80.4%) and MRSA (26.4%), followed by the perineal area, with rates of 27.6% and 12.6%, respectively. If only the nostrils had been investigated, the study would have failed to diagnose 17 patients (19.5%) as carriers of the pathogen into the ICU, thus contributing towards cross-dissemination.