SAN DIEGO – Among patients with MRSA bacteremia, age, markers of severity of acute treatment, and duration of treatment are predictive of mortality risk at 90 days and 1 year, a long-term single-center study showed.
At the annual Interscience Conference on Antimicrobial Agents and Chemotherapy, Renee-Claude Mercier, Pharm.D., presented results from an analysis which set out to describe the trajectory and long-term outcomes of patients with MRSA bacteremia, including the influence of bacterial, treatment, and host factors on outcomes.
Dr. Renee-Claude Mercier
Dr. Mercier and her associates identified 273 patients who were diagnosed with methicillin-resistant Staphylococcus aureus (MRSA) bacteremia during admission to the University of New Mexico Hospital between 2003 and 2013. The main outcomes were mortality at 90 days and 1 year, while secondary outcomes were hospital readmission, nursing home placement, and continued need for hemodialysis. Dr. Mercier, professor of pharmacy and medicine at the University of New Mexico, Albuquerque, and her associates used multivariable logistic regression and survival analysis to evaluate predictors of outcomes.
The mean age of the 273 patients was 52 years, 71% were male, and USA300 accounted for more than half of the strains (57%). A total of 66 patients (24%) died. “Importantly, we do not know the [mortality] status of 30% of our [study] population,” said Dr. Mercier. “We’re working right now with the [Centers for Disease Control and Prevention] to determine the cause or whether or not some of our patients that were included died in the 365 days following their infection with MRSA.”
At 30 days, the mortality rate was 17.7%, most commonly because of MRSA infection (75% of cases), followed by cancer (6.8% of cases) and secondary infection (2.3% of cases). The researchers followed the patients for a median of 237 days. Nearly half (44.8%) were discharged to home, 40.6% were discharged to a skilled nursing facility, and 2.9% returned to prison. “If patients were to die, they died in the first 30 days after infection with MRSA,” Dr. Mercier said. Independent predictors of mortality at 30 days included older age, the presence of liver disease, an ICU stay, a higher Pitt bacteremia score, and unresolved fever.
When the researchers excluded mortality that occurred in the first 30 days, the mortality rate at 90 days was 5.8%, mainly because of MRSA infection (in 46% of the cases), followed by other infection and unspecified sepsis (9%). On multivariable analysis, independent predictors of mortality at 90 days were use of mechanical ventilation (hazard ratio, 4.8; P = .02) and duration of treatment in days (HR .97; P = .078). “Treatment duration was an important determinant of survival in our study,” Dr. Mercier said. “Whether used as a continuous variable or as a dichotomous variable, using 4 weeks as our cutoff showed that the longer the treatment, the [greater the] decrease in mortality.”
After excluding mortality that occurred in the first 30 days, the researchers found that the mortality rate at 1 year was 17.8%, mainly because of MRSA infection (in 28% of the cases), followed by cancer (in 16% of cases) and secondary infections and unspecified sepsis (in 4% of cases). On multivariable analysis, independent predictors of mortality at 90 days were use of mechanical ventilation (HR 1.04; P = .005) and duration of treatment in days (HR .98; P = .05).
The majority of patients (64%) were not readmitted to the hospital within 1 year, while 16% were readmitted for other types of infections not related to S. aureus. In addition, 4% were readmitted because of cardiovascular causes, and 3% were readmitted because of a S. aureus infection.
Finally, Dr. Mercier and her colleagues performed a competing risk regression analysis examining different factors and their impact on mortality. Having an ICU stay as well as the presence of liver disease and receiving antibiotics for less than 4 weeks were significant predictors of mortality.
The researchers reported having no financial disclosures.