• Yiming Wang, Steven L Taylor, Jocelyn M Choo, Lito E Papanicolas, Rebecca Keating, Kate Hindmarsh, Rachel M Thomson, Lucy Morgan, Geraint B Rogers, and Lucy D Burr.
• Microbiome Research Laboratory, College of Medicine and Public Health, Flinders University, Adelaide, SA, Australia; Microbiome & Host Health, South Australia Health and Medical Research Institute, North Terrace, Adelaide, SA, Australia.
• Chest. 2022 Jul 1; 162 (1): 56-65.

BackgroundLong-term macrolide therapy has been shown to provide benefit to those with a range of chronic respiratory conditions. However, concerns remain about the impact of macrolide exposure on the carriage and abundance of antibiotic resistance genes within the oropharynx. The potential for onward transmission of resistance from macrolide recipients to their close contacts also is poorly understood.Research QuestionDoes long-term macrolide use impact carriage of resistance within the oropharyngeal microbiota in people with chronic respiratory conditions and risk of onward transmission to their close contacts?Study Design And MethodsOropharyngeal swabs were collected from 93 individuals with chronic respiratory conditions, 53 of whom were receiving long-term macrolide therapy. An oropharyngeal swab also was collected from a close cohabiting contact of each patient. Detection and abundance of 10 macrolide-associated resistance genes with the potential to disseminate via horizontal gene transfer were assessed by quantitative polymerase chain reaction analysis.ResultsDetection of resistance genes in macrolide recipients was comparable with that in nonrecipients. However, the normalized gene abundance of erm(B) was significantly higher in the macrolide recipient group (P = .045). Among the close contacts, no between-group differences in resistance gene detection or abundance were identified. Within-group analysis showed that the detection of erm(F) and mef in macrolide recipients, but not nonrecipients, was associated significantly with detection in close contacts (P = .003 and P = .004, respectively). However, between-group analysis showed that treatment group did not predict cocarriage between patients and their close contacts (P > .05 for each gene).InterpretationAlthough levels of erm(B) were higher in those receiving long-term macrolide therapy and evidence of gene cocarriage with close contacts was found, no evidence was found that macrolide use increased the onward transmission risk to their close contacts. This study therefore addresses concerns that long-term macrolide therapy could promote the dissemination of transmissible macrolide resistance.Copyright © 2022 American College of Chest Physicians. Published by Elsevier Inc. All rights reserved.

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