Treatment of MRSA Infection: Why Cultures Are Key

Dr Thomas Fekete's recent article on emerging infections (CONSULTANT, October 2007) was timely, given recent evidence that the incidence of methicillin-resistant Staphylococcus aureus (MRSA) infection, both hospital-acquired and community-acquired, has assumed pandemic proportions.¹ Invasive MRSA is now a major public health problem and is no longer confined to acute care settings. In fact, the incidence of community-onset MRSA infection (58.4%) is now twice that of hospital-onset MRSA infection.²

Dr Fekete mentioned the use of clindamycin in the outpatient treatment of MRSA. Some MRSA isolates are susceptible to clindamycin but resistant to erythromycin; however, these may have inducible clindamycin resistance (ICR).^3,4 When such isolates are identified, additional laboratory testing (the D test) is necessary before a serious infection can be treated with clindamycin alone. Because of ICR, physicians must note the pattern of MRSA resistance to erythromycin before treating solely with clindamycin. If the MRSA isolates are sensitive to clindamycin but resistant to erythromycin, the patient may benefit from an antibiotic other than clindamycin.

---- Aditya Gupta, MD
---- Shefali Goel Gupta, MD
Houston

Although minor to moderate MRSA infections can be managed with local care and oral therapy, it is prudent to obtain specimens for culture whenever possible so that we can use the clinical microbiology laboratory to optimize treatment. Some clinicians believe that they are saving resources by using empiric therapy; however, the cost of cultures is very modest and their implications can be huge. Without cultures, who can know when the next new pathogen has come along or whether the circulating strains are changing in their resistance phenotype?

It is disappointing that no clinical trials have compared the commonly used, inexpensive generic drugs-trimethoprim/sulfamethoxazole, doxycycline and clindamycin-in epidemic MRSA infection. Nonetheless, all 3 can play a role. In our clinical microbiology laboratory, ICR (as determined by the D test) is reported to the clinician. Although no one knows the exact failure rate of clindamycin in the treatment of infections caused by MRSA with erm-mediated erythromycin resistance, I agree that it is prudent to avoid clindamycin in patients with such infections.

I hope that the ongoing pandemic of MRSA infection will generate meaningful outcomes data for different therapeutic strategies so that we can offer our patients the most effective and safest treatment.

---- Thomas Fekete, MD
Professor of Medicine
Chief, Infectious Diseases
Temple University School of Medicine
Philadelphia

References:

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. 2007;298:1763-1771.

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Panagea S, Perry JD, Gould FK. Should clindamycin be used in treatment of patients with infections caused by erythromycin-resistant staphylococci?

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Gopal Rao G. Should clindamycin be used in treatment of patients with infections caused by erythromycin-resistant staphylococci?

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. 2000;45:715.