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Antimicrobial resistance linked to time since last antibiotic
In patients with previous exposure to antibiotics who present with invasive pneumococcal disease, the likelihood of antimicrobial resistance is largely predicted by the time elapsed since their most recent treatment course, according to recent findings.
In a report published in Clinical Infectious Diseases, researchers monitored invasive microbial disease in Toronto between 2002 and 2011. They documented all invasive pneumococcal infections identified by laboratories participating in the Toronto Invasive Bacterial Diseases Network, a compendium of hospitals, laboratories, infection control practitioners, physicians and public health units serving metropolitan Toronto and the Regional Municipality of Peel.
The researchers defined invasive pneumococcal infection as an illness in which Streptococcus pneumoniae was isolated from a normally sterile body site. Broth microdilution was utilized to determine antimicrobial susceptibility.
The researchers interviewed all patients — as well as next of kin, family physicians or hospitals — regarding history of antibiotic use 3 months prior to the date of a positive culture. Data on invasive pneumococcal disease and antimicrobial susceptibility were available for 4,062 (90%) cases. For 1,193 (29%) of these episodes, prior antibiotic courses had been administered within the past 3 months; a total of 1,782 antibiotic courses were recorded for these cases. Antibiotic resistance was analyzed based on antibiotic class.
The researchers found a significant association between the days since the last antibiotic and resistance against cephalosporins (adjusted OR=0.98; 95% CI, 0.96-1), macrolides (adjusted OR=0.98; 95% CI, 0.96-0.99), penicillins (adjusted OR=0.62; 95% CI, 0.44-0.89) and fluoroquinolones (adjusted OR=0.62; 95% CI, 0.39-1.04).
The fastest decrease in post-exposure risk of resistance — a return to baseline within 2 to 3 months — was observed in fluoroquinolones and penicillins. Macrolides showed the slowest decline in resistance, particularly azithromycin.
According to the researchers, the duration of antibiotic treatment was not related to resistance for any antibiotic class. Repeat courses could not be adequately analyzed because too few patients underwent multiple courses of the same antibiotic.
“In prospective surveillance of invasive pneumococcal disease, we were able to confirm the association between prior antibiotic use and pneumococcal resistance,” the researchers wrote. “Our results suggest that the time elapsed from most recent treatment and new infection is much more important than cumulative prior antibiotic exposure.”
Disclosure: Two of the researchers received grant support from and participated in advisory boards for Abbott Laboratories, Bayer Healthcare, Bristol-Myers Squibb Canada Co., GlaxoSmithKline, Hoffmann-La Roche and Pfizer.