Abstract
ObjectiveMass drug administration (MDA) with azithromycin for trachoma elimination reduces nasopharyngeal carriage of Streptococcus pneumoniae in the short term. We evaluated S. pneumoniae carried in the nasopharynx before and after a round of azithromycin MDA to determine whether MDA was associated with changes in pneumococcal population structure and resistance. MethodsWe analysed 514 pneumococcal whole genomes randomly selected from nasopharyngeal samples collected in two Gambian villages that received three annual rounds of MDA for trachoma elimination. The 514 samples represented 293 participants, of which 75% were children aged 0–9 years, isolated during three cross-sectional surveys (CSSs) conducted before the third round of MDA (CSS-1) and at 1 (CSS-2) and 6 (CSS-3) months after MDA. Bayesian Analysis of Population Structure (BAPS) was used to cluster related isolates by capturing variation in the core genome. Serotype and multilocus sequence type were inferred from the genotype. Antimicrobial resistance determinants were identified from assemblies, including known macrolide resistance genes. ResultsTwenty-seven BAPS clusters were assigned. These consisted of 81 sequence types (STs). Two BAPS clusters not observed in CSS-1 (n = 109) or CSS-2 (n = 69), increased in frequency in CSS-3 (n = 126); BAPS20 (8.73%, p 0.016) and BAPS22 (7.14%, p 0.032) but were not associated with antimicrobial resistance. Macrolide resistance within BAPS17 increased after treatment (CSS-1 n = 0/6, CSS-2/3 n = 5/5, p 0.002) and was carried on a mobile transposable element that also conferred resistance to tetracycline. DiscussionLimited changes in pneumococcal population structure were observed after the third round of MDA, suggesting treatment had little effect on the circulating lineages. An increase in macrolide resistance within one BAPS highlights the need for antimicrobial resistance surveillance in treated villages.
Highlights
Trachoma, caused by ocular infection with Chlamydia trachomatis, remains the leading infectious cause of blindness worldwide
mass drug administration (MDA) with azithromycin for trachoma elimination in The Gambia was associated with a short-term decrease in S. pneumoniae carriage [11]
Our results show little change in population structure following a round of MDA in communities where the number of circulating lineages was high and the prevalence of macrolide resistance low
Summary
Trachoma, caused by ocular infection with Chlamydia trachomatis, remains the leading infectious cause of blindness worldwide. R.A. Gladstone et al / Clinical Microbiology and Infection 27 (2021) 864e870 rate of children residing in treated villages was lower than that in untreated villages [3]. Gladstone et al / Clinical Microbiology and Infection 27 (2021) 864e870 rate of children residing in treated villages was lower than that in untreated villages [3] Another trial conducted in Niger, Tanzania and Malawi found biannual MDA with azithromycin significantly reduced all-cause under-5 mortality compared with placebo [5]. Other studies on azithromycin MDA for trachoma control have found an increased risk of azithromycin-resistant pneumococcal carriage [12,13] This has led to cautionary notes about the spread of antimicrobial resistance and requirements for adequate surveillance following MDA [14,15]
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