Laboratory analysis of Staphylococcus aureus in Florida from January 1, 2003 to December 31, 2005 with an emphasis on methicillin resistance

The Staphylococci are gram-positive bacteria that cause infections in humans and can produce severe morbidity and mortality. Methicillin resistant S. aureus (MRSA) isolates are resistant to all beta-lactam antibiotics, such as methicillin, and cephalosporins making treatment of these infections more difficult. MRSA has become prevalent throughout the United States, spreading in the health care setting and the community.The purpose of this study is to examine methicillin resistance among S. aureus isolates in an outpatient population in the state of Florida and asses possible associations between methicillin resistance and age group, gender, and geographic area. It is important to define methicillin resistance in a population so that clinical practice can adjust to the prevalence of resistance.The dataset used for this analysis is a record of all the S. aureus isolates tested by a large lab company in the state of Florida from January 1, 2003 to December 31, 2005. This is the first study to asses methicillin resistance with a population based dataset and not patients from hospitals. The percent of isolates that were methicillin resistant increased as year increased. This increase in the number of methicillin resistant isolates was significant for both the crude and adjusted analysis. When treated as a continuous variable and adjusted for age category, gender, and county of residence the odds ratio for year is 1.446, 95% CI: 1.410- 1.484. In 2005, 49.7% of the isolates were methicillin resistant. Methicillin resistance also varied by age category, gender, county, and region. For age group and gender the differences were not large and may not be clinically significant. However, there was substantial variation in methicillin resistance by region and county of residence.With nearly half of the S. aureus isolates being methicillin resistant, the beta-lactam antibiotics may no longer be an ideal choice for treating S. aureus infections in Florida. The percentage of MRSA isolates that were resistant to trimethoprim-sulfamethoxazole, tetracycline, gentamycin, and rifampin was low. These antibiotics may be feasible alternatives to treat outpatient S. aureus infections in Florida