Invasive MRSA

Staphylococcus (or “staph”) is a type of bacteria that can cause several different illnesses in humans, including skin infections, pneumonia, and food poisoning. Staphylococcus aureus is the most common organism causing staph infections. About one in every three people has Staphylococcus aureus in their nose but not all of these individuals (“carriers”) will develop symptoms.¹ Infections occur when staph bacteria enter openings or tears in the skin. Staphylococcus aureus bacteria that can survive in the presence of certain antibiotics are known as MRSA.

Invasive MRSA can be contracted in hospital settings through improper infection control (e.g. poor hand hygiene), leading to bloodstream infections or pneumonia. It can also be contracted in long-term care facilities (e.g. nursing homes) or in the community.

Invasive MRSA is a reportable condition in Allegheny County. Hospitals are required to report any MRSA-positive cultures collected from a normally sterile site in the body using the ACHD’sonline reporting form. These data are monitored to identify potential clusters of disease in time or location and to summarize the burden of invasive MRSA in Allegheny County.

The Centers for Disease Control and Prevention (CDC) estimated that about 72,000 invasive MRSA infections occurred in the U.S. in 2014.2In 2018, hospitals in Allegheny County reported 138 cases of invasive MRSA, including 3 recurrent infections3, to the ACHD. Most (89%) invasive MRSA cases involved bloodstream infections (Table 1). Death was reported in 7% of cases. Most persons with invasive MRSA were male (59%) and about half were ≥65 years of age (Table 2). Among those with available risk factor data, a majority had had a previous MRSA infection (Table 3).

Cases are often classified as hospital-onset (HO), healthcare-associated community-onset (HACO), or community-associated (CA) to describe where exposure might have occurred. Cases are classified as HO when a positive MRSA culture is obtained more than three calendar days after admission to the hospital. If the positive culture was obtained in the outpatient setting or within three calendar days of admission and the patient has either 1) a history of hospitalization, surgery, dialysis, or residence in a long term care facility in the past year or 2) the presence of a central vascular catheter two or less days prior to culture, then the case is defined as HACO. All other cases are classified as CA. Of the 135 individuals known to have a least one invasive MRSA infection, 10 were HO, 75 were HACO, and 18 were CA. The remaining 32 cases could not be classified due to missing or unknown information.

Invasive MRSA can be prevented from spreading in the community by practicing good hand and body hygiene, covering open cuts or sores, and avoiding sharing personal items like razors. Proper use of contact precautions and personal protective equipment, as well as proper disinfection of surfaces and laundry, can help prevent the spread of invasive MRSA in healthcare settings.