Multiple distinct outbreaks of Panton-Valentine leucocidin-positive community-associated meticillin-resistant Staphylococcus aureus in Ireland investigated by whole-genome sequencing

Background: Panton-Valentine leucocidin (PVL)-positive community-associated meticillin-resistant Staphylococcus aureus (CA-MRSA) is increasingly associated with infection outbreaks. Aim: To investigate multiple suspected PVL-positive CA-MRSA outbreaks using wholegenome sequencing (WGS). Methods: Forty-six suspected outbreak-associated isolates from 36 individuals at three separate Irish hospitals (H1 -H3) and from separate incidents involving separate families associated with H2 were investigated by whole-genome multi-locus sequence typing (wgMLST). Findings: Two clusters (CH1 and CH2) consisting of 8/10 and 6/6 PVL-positive t008 ST8MRSA-IVa isolates from H1 and H2, respectively, were identified. Within each cluster, neighbouring isolates were separated by <5 allelic differences; however, >73 allelic differences were identified between the clusters, indicating two independent outbreaks. Isolates from the H3 maternity unit formed two clusters (CH3-SCI and CH3-SCII) composed of four PVL-negative t4667 ST5-MRSA-V and 14 PVL-positive t002 ST5-MRSA-IVc isolates, respectively. Within clusters, neighbouring isolates were separated by <24 allelic differences, whereas both clusters were separated by 1822 allelic differences, indicating two distinct H3 outbreaks. Eight PVL-positive t127 ST1-MRSA-V+fus and three PVLnegative t267 ST97-MRSA-V+fus isolates from two distinct H2-associated families FC1 (N = 4) and FC2 (N = 7) formed three separate clusters (FC1 (t127), FC2 (t127) and FC2 (t267)). Neighbouring isolates within clusters were closely related and exhibited <7 allelic differences. Intrafamilial transmission was apparent, but the detection of >48 allelic differences between clusters indicated no interfamilial transmission. Conclusion: The frequent importation of PVL-positive CA-MRSA into healthcare settings, transmission and association with outbreaks is a serious ongoing concern. WGS is a highly discriminatory, informative method for deciphering such outbreaks conclusively. 2020 The Author(s). Published by Elsevier Ltd on behalf of The Healthcare Infection Society. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

This study investigated multiple suspected PVL-positive CA-MRSA outbreaks using whole-genome sequencing, identifying independent outbreaks and intrafamilial transmission. Whole-genome sequencing is a highly discriminatory method for deciphering outbreaks.