BACKGROUND: Methicillin-resistant Staphylococcus aureus(MRSA), a common cause of skin infections resistant to multiple antibiotics, can spread to normally sterile sites, causing more lethal illness known as invasive MRSA. National surveillance systems indicate that >70,000 cases of invasive MRSA occurred in the US in 2014. In Allegheny County, PA, required MRSA reporting was changed to include only invasive cases in 2014, and a new reporting form was developed. The objective of this analysis is to summarize the demographic and clinical characteristics of reported invasive MRSA cases, describe risk factors, and assess degree of underreporting.
METHODS: Invasive MRSA reports are faxed to the Allegheny County Health Department (ACHD) by health care providers. ACHD staff computerizes and analyzes the data using EpiInfo software. This analysis is limited to a description of reported cases with date of specimen collection from January 2015 through September 2016. A separate analysis of hospital inpatient stays in 2015 with a MRSA septicemia billing code (ICD-9 code 038.12 and IDC-10 code A41.02) was conducted using Pennsylvania’s de-identified hospital discharge database for comparison purposes.
RESULTS: Health care providers reported 131cases of invasive MRSA to ACHD with specimen collection date in 2015 and 94 in January through September 2016 for a total of 225. Of the 219 cases with known age, the median was 66 years (range 7 to 100 years). Of the 216 cases with known sex, 58% were male, and of the 195 with known race, 85% were white. All cases were diagnosed by culture with specimen source blood (87%), bone (4%), joint/synovial fluid (3%), pleural fluid (2%), or CSF (0.4%); nine (4%) cases had >1 positive culture site. Forty percent of cases were known to have a previous MRSA infection and 55% were known to have been admitted to a health care facility within a year. Nine (4%) deaths were reported. Hospital inpatient stays in 2015 for Allegheny County residents with an ICD code for MRSA septicemia totaled 263, more than twice the number of faxed reports.
CONCLUSIONS: Passive population–based surveillance of invasive MRSA in Allegheny County appears to capture slightly less than half the cases but provides more timely and in-depth information than hospital discharge data. Given that most invasive cases may be associated with either a previous MRSA infection or admission to a health care facility within the previous year, steps to prevent recurrent MRSA are essential.