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Bug basics: Is it staph, MRSA, or CA-MRSA?
Basic infection control principles same for all
• What is Staphylococcus aureus and MRSA?
Staphylococcus aureus — often referred to simply as "staph" — are bacteria commonly carried on the skin or in the nose of healthy people. Approximately 25%-30% of the population is colonized (when bacteria are present, but not causing an infection) in the nose with staph bacteria. Staph can cause both minor skin infections and serious bloodstream infections, but these can be treated with antibiotics. Some staph bacteria become resistant to groups of antibiotics and the resulting infections can become more serious if the right antibiotic is not used on the patient. The main culprit in this group is called methicillin-resistant S. aureus (MRSA), which is resistant to such common antibiotics as oxacillin, penicillin, and amoxicillin. Staph infections, including MRSA, occur most frequently among patients in hospitals and health care facilities (such as nursing homes and dialysis centers) who have weakened immune systems. These health care- associated staph infections include surgical wound infections, urinary tract infections, bloodstream infections, and pneumonia.
• What is community-associated MRSA (CA-MRSA)?
MRSA infections that are acquired by persons who have not been recently (within the past year) hospitalized or had a medical procedure (such as dialysis, surgery, catheters) are known as CA-MRSA infections. CA-MRSA infections in the community are usually manifested as skin infections, such as pimples and boils, and occur in otherwise healthy people. Recently recognized outbreaks of CA-MRSA have been associated with strains that have some unique microbiologic and genetic properties compared with the traditional hospital-based MRSA strains, suggesting some biologic properties (e.g., virulence factors) may allow the community strains to spread more easily or cause more skin disease. There are at least three different S. aureus strains in the United States that can cause CA-MRSA infections, but the primary emerging strain is called USA300.
• What are the clinical features of CA-MRSA?
CA-MRSA most often presents as skin or soft-tissue infection such as a boil or abscess. Patients frequently recall a "spider bite." The involved site is red, swollen, and painful and may have pus or other drainage. Staph infections also can cause more serious infections, such as blood-stream infections or pneumonia, leading to symptoms of shortness of breath, fever, and chills.
• What about treatment of these infections?
Staph skin infections, such as boils or abscesses, may be treated by incision and drainage, depending on severity. Antibiotic treatment, if indicated, should be guided by the susceptibility profile of the organism. If S. aureus is isolated, the organism should be tested to determine which antibiotics will be effective for treating the infection. Ambulatory settings that outsource microbiology laboratory services should specify by contract that the laboratory provide either facility-specific susceptibility data or local or regional aggregate susceptibility data to identify prevalent drug-resistance trends and pathogens in the geographic area served.
• Who is at risk for CA-MRSA or MRSA infections?
CA-MRSA infection can occur in anyone, but clusters of skin infections have particularly been noted among athletes, military recruits, children, Pacific Islanders, Alaskan Natives, Native Americans, men who have sex with men, and prisoners. The main mode of transmission is via hands, which may become contaminated by contact with a) colonized or infected individuals; b) colonized or infected body sites of other persons; or c) devices, items, or environmental surfaces contaminated with body fluids containing CA-MRSA. Other factors contributing to transmission include skin-to-skin contact, crowded conditions, and poor hygiene. Emerging reports suggest health care workers also may be at risk of CA-MRSA if they do not follow basic infection control precautions when treating patients.
(Editor's note: The answers above were compiled and summarized from guidelines by the Centers for Disease Control and Prevention and interviews with its investigators.)