Default model parameters of the basic model.

*Average transmission and discharge rate in the US (see methods section); for age-class dependent rates see Figure 1.
**Average number of antibiotic prescriptions in the US (data from the data from the National Ambulatory Medical Care Survey (NAMCS) and the National Hospital Ambulatory Medical Care Survey (NHAMCS)); see Table S1.
***Polk et al [20] measured antibiotic use in 130 US hospitals. They found that 60% of all discharged patients received at least one dose of an antibacterial drug. With an average length of stay of 4 days (see *) a daily treatment rate of 0.2 leads to 0.55% of patients receiving treatment during their stay.
#fX,Y was calculated as the fraction of drugs used in setting X that are effective against the strain Y (see methods section).
##The basic reproductive ratio of CA-MRSA in community was determined under the assumption that this strain pays no cost of resistance; i.e. it has the same transmission rate as methicillin-sensitive S aureus. The latter colonizes about 30% of individuals in the community and with an R0 of 1.4 the expected prevalence is 1-1/1.4 = 0.29.
###The single-admission basic reproductive number of HA-MRSA in the hospital corresponds to the number of secondary infections caused by a single colonized individual admitted to a hospital containing only susceptible individuals and is given by the dominant eigenvalue of the next-generation matrix B V−1. The matrix B is given by Bij = βHA,Hij Si, [with Si the frequency of susceptibles of age-class i in the disease-free equilibrium in the hospital. In the absence of age structure Si = a/d for all i. In the presence of age structure Si = ai/di *(the proportion of the total population in age group i) (see Figure 2)]. The matrix V is given by Vij = dj+cBL+τH cT fH,HA for i = j and Vij = 0 for i≠j.