How common is MRSA as a cause of cellulitis?

Updated: Jun 14, 2019
  • Author: Thomas E Herchline, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Answer

Although cellulitis can be complicated by abscess formation, it typically develops from an abscessogenic focus. One maxim in microbiology is the following: "The hallmark of staph infection is abscess formation." This has become a significant concern because of changing patterns of antibiotic resistance of S aureus, particularly MRSA. [37]

MRSA was first reported in 1968 [38] ; for years, MRSA infections were identified only in patients with recent hospitalization, surgery, renal dialysis, residence in long-term-care facilities, or IV drug use. However, in the 1990s, isolates of S aureus were found in patients without risk factors for nosocomial disease. [39] These isolates, which mostly maintain susceptibility to antibiotics such as trimethoprim-sulfamethoxazole or tetracycline, have been termed CA-MRSA to distinguish them from the previously identified hospital or health-care-associated MRSA (HA-MRSA). (See the images below.)

Patient with cellulitis of the left ankle. This ce Patient with cellulitis of the left ankle. This cellulitis was caused by community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). (Photo courtesy of Texas Dept. of Public Health.)
Abscess and associated cellulitis caused by commun Abscess and associated cellulitis caused by community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). (Photo courtesy of Texas Dept. of Public Health.)

Although reports have indicated that MRSA causes the majority of skin and soft-tissue infections (SSTIs), these studies are plagued by variability in case-finding methodologies. [40] Furthermore, in the context of cellulitis, the finding is misleading in that these reports come from analysis of wound cultures in cases in which abscess formation occurred. Cultures in cellulitis are difficult to perform and frequently do not yield positive results; therefore, these tests are rarely done clinically. Consequently, the results of these studies cannot be generalized to cellulitis without abscess formation. Studies are under way to determine the incidence of S aureus —in particular, CA-MRSA in soft-tissue infection in which there is no identifiable abscess. However, until results of those studies are available, treatment decisions must be made on clinical grounds. Because treatment failures after empiric treatment may often occur, because of the emergence of resistantstrains,microbiologicinvestigations are strongly recommended.


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