Prosthetic joint infection (PJI) represents one of the most common reasons for failure among hip and knee arthroplasty, with an incidence of around 1-2%. Infection can occur early (within days of surgery) or late (over a year after surgery), and no specific early markers for infection onset exist. Given the significant costs to the NHS for corrective revision surgery, the added suffering and risks to patients from surgery, and the risk of enhancing antimicrobial resistance through the use of broad-spectrum antibiotics, a more specific predictive test for early onset of infection is required.