Stewardship / Resistance Scan for Apr 11, 2019

Macrolide-resistant Mycoplasma
MRSA rapid tests
Penicillin allergy mislabeling

Study finds high rates of macrolide-resistant M genitalium in Chinese men

Chinese and US researchers report today in Clinical Infectious Diseases that macrolide use is associated with an almost double rate of antibiotic resistance in urethritis caused by Mycoplasma genitalium in men, and a related commentary questions whether it's time for the US and Canada to reconsider macrolides as first-line empiric treatment for men with symptomatic urethritis.

The investigators tested 1,816 Chinese men who had symptomatic urethritis, 358 of whom (19.7%) were infected with M genitalium. The men who had taken macrolides had a 96.7% higher rate of macrolide resistance than those who had not taken the drugs. The researchers also noted that 88.9% of M genitalium isolates harbored genes with mutations conferring macrolide resistance, and 89.5% had genes responsible for fluoroquinolone resistance.

In a related commentary, Ameeta Singh, BMBS, MSc, of the University of Alberta, and Lisa Manhart, PhD, of the University of Washington, challenge the use of macrolides in non-gonococcal urethritis (NGU) in men. They say the high prevalence of both M genitalium and macrolide resistance "has called into question the routine use of macrolides (single dose azithromycin) for the empiric treatment of NGU" in Canada and the United States.

They note that recent UK, European, and Australian guidelines for managing NGU now recommend against azithromycin for routine first-line treatment.
Apr 11 Clin Infect Dis abstract
Apr 11 Clin Infect Dis commentary


Researchers show variations in accuracy of 3 XpertMRSA versions

Swiss researchers evaluated three consecutive versions of the XpertMRSA rapid test (G3, Gen3, and NxG) for detecting methicillin-resistant Staphylococcus aureus (MRSA), finding that the sensitivity improved with each successive commercial version, but not statistically significantly, while specificity and positive likelihood ratios were significantly lower in the Gen3 version.

Writing in Clinical Microbiology and Infection, the scientists say they simultaneously screened MRSA samples by culture and rapid polymerase chain reaction via the three XpertMRSA tests, the earliest version of which was G3. They analyzed 3,512 samples by G3, 2,794 by Gen3, and 3,288 by NxG.

Among the three groups, 5.0%, 4.7%, and 4.3% of samples, respectively, tested positive for MRSA by culture. The sensitivity of the XpertMRSA rapid test improved with each newer version (71.4, 82.3, and 84.3%, respectively), but non-significantly. The specificity (98.4, 96.8, and 99.1, respectively) and the positive likelihood ratios (45.7, 25.6, and 97.1, respectively) were significantly lower in the Gen3 version (P <0.00001).

The authors conclude, "These significant differences in performance shows the importance to evaluate each new version of a commercial test."
Apr 4 Clin Microbiol Infect study


Study: 2.7 million penicillin allergies in the UK incorrect

Up to 2.7 million people in the United Kingdom with documented penicillin allergies (PenA) on  their medical charts do not have a true allergy, according to a report yesterday in the Journal of Antimicrobial Chemotherapy.

This was the first study to assess the prevalence of PenA designation in the United Kingdom, the authors said, and it was conducted by examining electronic medical records from the British National Health Service over the course of 1 year (2013-2014). PenA prevalence was 5.9%, and was more common in the elderly and in female patients.

PenA was also associated with an increased risk of re-prescription of a new antibiotic class within 28 days (relative risk [RR], 1.32), MRSA infection/colonization (RR, 1.90) and death during the year subsequent to the study (RR, 1.08). The total number of antibiotic prescriptions was increased in patients with PenA, the authors said.

PenA is one of the most common drug allergies and causes clinicians to use different and in many cases more antibiotics when prescribing to patients with a PenA note in their medical charts. The researchers estimate that 2.7 million people in England have incorrect PenA records.

Conducting a true oral challenge for patients with a PenA designation could help with more precise antibiotic prescribing, the authors concluded, as many patients have been designated a PenA for adverse reactions that do not represent a true allergy.
Apr 10 J Antimicrob Chemother

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