Drug-Susceptible S. aureus Still Dangerous

Abstract

Bruce Jancin is with the Denver bureau of Elsevier Global Medical News. VIENNA – Methicillin-resistant Staphylococcus aureus bloodstream infections grab the headlines and are the focus of many infection-prevention directives, but methicillin-susceptible S. aureus infections, which receive far less attention, have comparable morbidity and mortality, according to two European studies. “MSSA bloodstream infection is MRSA's evil twin,” Michael Laum, MD, said at the European Congress of Clinical Microbiology and Infectious Diseases. He compared key outcomes for 52 patients with MSSA bloodstream infection and 16 with MRSA bloodstream infection at Blackpool Victoria Hospital in Lancashire, England, during a 20-month period starting in November 2007. There were far fewer cases of MRSA infection because incidence plunged by 78% in the year after the hospital introduced a comprehensive MRSA containment program. The average length of stay was 23.2 days for patients with MSSA infection and 26.3 days with MRSA. The MSSA patients averaged 61 years of age, the MRSA patients 71. Eighteen percent of MSSA patients were admitted to intensive care, as were 19% with MRSA. In-hospital mortality was 34% in the MSSA patients and 44% in the MRSA group. The average Acute Physiology and Chronic Health Evaluation (APACHE) II score at the time blood cultures were obtained was 13 points in the MSSA group and 16 for the MRSA patients. Eighty-four percent of the MSSA patients had optimal antibiotics initiated before their blood culture results were known, as did just 54% of those with MRSA. Seventy-one percent of MSSA infections and 80% of MRSA infections had their onset less than 48 hours after patient hospitalization, strongly suggesting community-acquired infection. The lesson of the study is mandatory MRSA screening and surveillance program ought to be expanded to incorporate MSSA, concluded Dr. Lau of the hospital's general surgery department. A similar point was made in the Burden of Resistance and Disease in European Nations (BURDEN) study presented by Marlieke de Kraker of the National Institute for Public Health and the Environment, Bilthoven, the Netherlands. BURDEN included all adult patients with MRSA or MSSA bloodstream infection at a tertiary care hospital in each of 13 European countries during a 1-year period. The study population comprised 248 patients with MRSA and 453 controls matched for age, Charlson Comorbidity Index score, and duration of hospital stay before infection, along with 618 patients with MSSA and 1,170 matched controls. Patients with MSSA often present with a different clinical picture than do those with MRSA, Ms. de Kraker said. Patients with MRSA infection tend to be older and have more comorbidities. In-hospital mortality occurred in 36% of the MRSA group and 9% of their controls, and in 23% of the MSSA group and 7% of their controls. In a multivariate analysis, MRSA infection was associated with a 3.5-fold increased risk of in-hospital mortality, and MSSA carried a 3.1-fold increased mortality risk compared with controls. Another multivariate analysis demonstrated that bloodstream infection with MRSA added an average of 9.2 days to the length of a hospital stay, while MSSA resulted in an extra 8.6 days, she reported. “The burden of S. aureus bloodstream infections in the hospital is high, for MRSA as well as MSSA. Methicillin resistance does not seem to be associated with excess length of stay or mortality. Infection prevention should be aimed at decreasing the number of S. aureus bloodstream infections, irrespective of methicillin susceptibility,” Ms. de Kraker said. Dr. Lau and Ms. de Kraker each reported having no financial conflict.