Staphylococcus aureus bacteremia: comparison of two periods and a predictive model of mortality

ABSTRACT

Staphylococcus aureus is an important pathogen causing bacteremia, primarily affecting hospitalized patients. We studied the epidemiology of S. aureus bacteremia, comparing two periods (early and mid 1990s) and developed a predictive model of mortality. A nested case-control was done. All 251 patients over 14 years old with positive blood cultures for S. aureus were selected. MRSA (methicillin resistant S. aureus) was isolated in 63 percent of the cases. When comparing the two periods MRSA community-acquired bacteremia increased from 4 percent to 16 percent (p=0.01). There was no significant difference in the mortality rate between the two periods (39 percent and 33 percent, p=0.40). Intravascular catheters provoked 24 percent of the cases of bacteremia and were associated with the lowest rate of mortality. In a logistic regression analysis, three variables were associated with death septic shock, source of bacteraemia and resistance to methicillin. The probability of dying among patients with MRSA and those with methicillin sensitive S. aureus bacteraemia ranged from 10 percent to 90 percent and from 4 percent to 76 percent, respectively, depending on the source of the bacteraemia and the occurrence of septic shock. The MRSA found in Brazil may be a particularly virulent strain.