This study will determine the frequency of Staphylococcus aureus carriage in household contacts of individuals with clinical infection due to this pathogen. It will also assess the frequency of transmission events over the following three months. Finally it will aim to identify predisposing characteristics both on a demographic/social level as well virulence characteristics of the identified strains.

This is a prospective cohort study based at Anuradhapura Teaching Hospital (Sri Lanka). Potential index study participants will have clinical infection caused by Staphylococcus aureus and will be identified from hospital microbiology laboratory records within 48 hours of admission. With consent, the investigators will approach up to 4 household members for participation in the carriage study. With their consent, household members will have swabs collected on 2 occasions 3 months apart. All hospitalised patients will receive standard-of-care treatment in accordance with local practice and national guidance. Clinical, demographic and social/lifestyle data will be collected from index patients and households by scheduled interview performed by local investigators. Bacterial isolates from the initial index patient infection, and those identified through household member screening will be assessed for antimicrobial susceptibility, virulence factor repertoire and analysed by whole genome sequencing. While infection with the cc5 MRSA clone has been described in several hospital and hospital-associated settings in South Asia a major unresolved issue is whether transmission and circulation of this clone is occurring in community settings. In this study the investigators will investigate and characterise the household circulation of Staphylococcus aureus strains, exploring differences in bacterial virulence characteristics and host susceptibility factors associated with increased risk of carriage. Understanding these factors and estimating the burden of disease which may be occurring in the community setting will allow more accurate assessment of the risk posed by cc5 PVL-MRSA to similar Low and Middle Income Countries (LMIC) settings and signal potential routes to mitigation through treatment optimisation and disease prevention including infection control or vaccination.

Inclusion Criteria (index patient):

• Confirmed clinical infection caused by Staphylococcus aureus infection, including skin and soft tissue infection (SSTI) or infection of a normally sterile site.
• Participant is willing and able to give informed consent for participation in the study.
• Male or Female greater or equal to 18 years old.
• Household is within one day's travel of the Hospital.

Inclusion Criteria (household contact):

• Resident in the same household as index participant.
• Participant is willing and able to give informed consent for participation in the study if greater or equal to 18 years old or the parent/legal guardian if participant is less than 18 years old.
• Likely continued household residence for at least 3 months from initial sample collection.
• Able to comply with study requirements.

Exclusion Criteria (index patient):

- Deemed unsuitable by the responsible clinical team/clinician (e.g. terminal illness).

Exclusion Criteria (household contact):

• Not a resident of the household at the time of the index patient hospital admission.
• Deemed unsuitable by the responsible clinical team/clinician (e.g. terminal illness)
• At least 4 household contacts already enrolled to this study.

The index patients will have clinical infection due to Staphylococcus aureus identified during admission to Anuradhapura General Hospital.

The household contacts will be resident in the same household as the index patient so will be part of the local community served by Anuradhapura General Hospital.