A prospective cohort study to investigate the transmission and burden of Staphylococcus aureus in Sri Lanka

Methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) is a common cause of infection in both community and healthcare settings, and the household may be a central component linking these two environments. Strategies to prevent <i>S. aureus</i> transmission and thereby reduce the risk of infection must be informed by a detailed understanding of local epidemiology. These data are typically lacking in many low- and middle-income countries. Therefore, we aimed to investigate the circulation of infecting <i>S. aureus</i> strains in Sri Lanka, with a focus on the community and healthcare interface. A prospective longitudinal cohort study was performed between July and December 2021. Index patients with <i>S. aureus</i> infection and up to four of their household contacts were enrolled in the study. Colonization was assessed by sampling participants' nose and axilla at two time points over 3 months of follow-up. Whole-genome sequencing (WGS) was used to characterize isolates and assess strain similarity to identify transmission episodes and environmental clusters. A total of 153 participants were recruited, including 42 <i>S</i>. <i>aureus</i>-positive index patients and 111 household contacts. The baseline prevalence of <i>S. aureus</i> colonization amongst household contacts was 11.7% (13/111), of which 30.8% (4/13) were methicillin-resistant. A total of 88 <i>S</i>. <i>aureus</i> isolates underwent WGS and three multilocus sequence types predominated: ST672, ST5 and ST6. Each type had unique virulence characteristics but was identified in both community and healthcare environments. Colonization of household members with the index's infecting strain was not detected. <i>S. aureus</i> is a major cause of morbidity and mortality in low-resource settings such as Sri Lanka, yet little is known about risk factors and transmission networks. In this descriptive study, we have identified a small number of strains that appear to be well established and capable of causing both severe infection and asymptomatic colonization. Transmission of <i>S. aureus</i> did not appear to be occurring frequently in the household, and, therefore, preventative strategies that target high-risk groups may be more successful than universal community-based measures.