bacterial infections

Penicillin Allergy Raises MRSA, C difficile Risks

The risks for methicillin-resistant Staphylococcus aureus (MRSA) and Clostridium difficile (C difficile) are elevated among patients with a documented penicillin allergy, especially among those taking β lactam alternative antibiotics.

These findings emerged from a study of 301,399 adults without previous MRSA or C difficile who were enrolled in the UK Health Improvement Network database. Of these patients, 64,141 had a penicillin allergy, and 237,258 served as controls. Mean follow-up lasted 6.0 years.

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The primary outcomes of the study were the risks for incident MRSA and C difficile, and secondary outcomes included the use of β lactam antibiotics and β lactam alternative antibiotics.

A total of 1365 patients developed MRSA and 1688 developed C difficile. Of the patients that developed MRSA, 442 had penicillin allergy (adjusted hazard ratio [aHR] 1.69), and 923 did not. Among patients that developed C difficile, 442 had penicillin allergy (aHR 1.26), and 1246 did not.

The adjusted incidence rate ratios for antibiotic use among patients with penicillin allergy were:

  • 4.15 for macrolides
  • 3.89 for clindamycin
  • 2.10 for fluoroquinolones

Perhaps most notably, 55% of the elevated risk of MRSA and 35% of the elevated risk of C difficile were due to increased use of β lactam alternative antibiotics.

“Documented penicillin allergy was associated with an increased risk of MRSA and C difficile that was mediated by the increased use of β lactam alternative antibiotics,” the researchers concluded. “Systematically addressing penicillin allergies may be an important public health strategy to reduce the incidence of MRSA and C difficile among patients with a penicillin allergy label.”

—Christina Vogt

Reference:

Blumenthal KG, Lu N, Zhang Y, Li Y, Walensky RP, Choi HK. Risk of methicillin resistant Staphylococcus aureus and Clostridium difficile in patients with a documented penicillin allergy: population based matched cohort study. BMJ. 2018;361. https://doi.org/10.1136/bmj.k2400