aureus de novo, 5 highlighting the importance of using strain typing to identify truly persistent carriage. Assuming those followed long enough to identify this group were representative, “spa-consistent” long-term carriers would comprise 17% of those enrolled. Interestingly, two-thirds of these “spa-consistent” long-term carriers never had any other strain identified despite the long follow-up and the fact that multi-strain colonisation was actively investigated. We found that the rate of new acquisitions increased linearly through the study (Fig. 3) and the proportion never observed to carry correspondingly decreased linearly (Fig. 5(b)). Our data

are thus compatible with van Belkum’s AZD8055 suggestion, based on experimental inoculation studies,19 that there are no true S. aureus non-carriers, i.e. that a fourth “never carriage” group does not exist. Whilst 90 participants returning ≥12 swabs never had S. aureus isolated from any study sample, the highly transient carriage that was observed suggests it could have been found at intermediate timepoints. Extrapolating from Fig. 3, 5–10 years follow-up would be needed to distinguish a never carriage phenotype (where the cumulative new acquisition BI 6727 solubility dmso probability would plateau) from continued acquisitions (where the cumulative new acquisition probability would reach 100%). The former scenario would imply that host, rather than bacterial, genetics determines this

phenotype. Despite this being the largest longitudinal study of S. aureus carriage to date, we failed to find strong predictors of gain, loss or persistence, possibly reflecting multifactorial causes and limited power to detect modest absolute differences of around 10%, given that the study was powered to detect 15% differences. Overall effects on loss, gain,

and persistence were broadly compatible, although these reflect subtly different aspects of the underlying dynamics. Host Adenylyl cyclase effects likely reflected potential for S. aureus exposure (household members, students), underlying host-immunity (age, previous MSSA), and complex effects of health status (long-term illness, recent outpatient appointments). Interestingly receiving anti-staphylococcal antibiotics significantly increased the likelihood of losing S. aureus in the next swab, but also increased the likelihood of later acquisition. This is consistent with antibiotics only temporarily removing S. aureus from the nares, followed by re-acquisition from other body sites/close contacts, as in one study of artificial decolonisation and re-colonisation. 19 These findings question the validity of S. aureus eradication as a concept, and suggest that reducing S. aureus load around high-risk procedures (e.g. through decontamination/prophylaxis pre-surgery) is a more biologically plausible approach to reducing S. aureus infection risk. Unexpectedly, we found large effects of spa-type on acquisition and long-term consistent carriage.