MRSA: Growing epidemic mandates high index of suspicion

May 01, 2008, 4:00am

Cutaneous infections caused by methicillin-resistant Staphylococcus aureus are being seen in communities nationwide. A high index of suspicion should be maintained for this diagnosis, even in patients without identifiable risk factors. Incision and drainage, appropriate antibiotic treatment and institution of hygienic measures are critical components of infection control.

Key Points

"Skin and soft tissue MRSA infection is occurring in virtually every community and will be with us for quite a while, until future strategies make it a historical footnote," says Dr. Heymann, professor of medicine and pediatrics and head of the division of dermatology, UMDNJ-Robert Wood Johnson Medical School, Camden, N.J.

"Therefore, dermatologists need to maintain an index of suspicion for MRSA, so that it will be recognized promptly and treated effectively before the infection progresses," Dr. Heymann tells Dermatology Times.

"People who live in crowded or poor socioeconomic conditions are at increased risk for MRSA, but clearly, others can be affected as well.

"Lack of good personal hygiene or basic infection control principles, recent hospitalization and contact with infected individuals are also risk factors," Dr. Heymann says.

Treatment algorithm

Incision and drainage continues to be the cornerstone for treatment of any skin infection suspected to be MRSA.

Given the current epidemic, Dr. Heymann says that lesional material should be obtained from all patients and sent for culture to establish the diagnosis and obtain antibiotic susceptibility data.

"There are now reports of lymphangitic streaks associated with MRSA, so even if you think an infection is streptococcal and there is any material available for culture, please submit it, because you might change your mind about the diagnosis," Dr. Heymann says.

Antibiotics should be prescribed judiciously, taking into account a variety of patient-related factors and in vitro susceptibility data.

Some experts suggest that after incision and drainage are performed, antibiotics are not needed in immunocompetent patients who are otherwise well.

However, empiric therapy with an oral antibiotic may be considered as adjunctive treatment to incision and drainage, particularly if there is purulent drainage and the infection seems to be progressing rapidly.

At the other end of the spectrum, patients who are seriously ill must be hospitalized, and are candidates for initiation of intravenous antibiotic therapy, probably with vancomycin, Dr. Heymann says.

Antibiotic selection is guided initially by local antibiotic resistance patterns and, ultimately, by results from microbiological testing.

Other factors to consider include patient age, medication cost and allergies.

Recommendations for antibiotic treatment are evolving with changing resistance patterns.

Doxycycline and minocycline continue to have good in vitro activity against community-derived strains of MRSA, but emerging resistance in some geographic areas indicates their role as empiric therapy may need to be reassessed in the future.

Fluoroquinolones were previously considered a first-line choice, but are no longer recommended because of high rates of MRSA resistance.

Failures have also been reported in patients treated with trimethoprim-sulfamethoxazole, and very recent information indicates they may be mediated in part via a novel mechanism involving bacterial thermonuclease that releases thymidine from DNA.

Clindamycin may be effective in treating MRSA infections, but inducible clindamycin resistance can occur and lead to treatment failures.

The presence of inducible clindamycin resistance is evaluated using the D-test, and dermatologists should check to make sure this assay is performed by their microbiology laboratory.

Rifampin is highly active against susceptible CA-MRSA, but mutations occur at a high frequency, so this agent should be used only in combination with trimethoprim-sulfamethoxazole or doxycycline, never as monotherapy.