Temporal dynamics of clade IC1 in Iceland. (A) Bayesian skyline plot of the product of effective population size and generation time over the course of the outbreak. The median estimate of this parameter is displayed as the black line, while the 95% credibility interval is indicated by the blue filled area. The solid red line indicates the recorded numbers of penicillin non-susceptible pneumococci of serotype 6B collected from cases of disease in Iceland between 1989 and 1995. The dashed red line indicates the available figures for the number of clinical isolates meeting these criteria collected from the Capital and Southwestern areas from 1995 onwards, which account for more than 90% of the penicillin non-susceptible pneumococci identified in Iceland . (B) Proportion of clade IC1 isolates resistant to tetracycline, erythromycin and chloramphenicol over time. The total number of sequenced isolates from clade IC1 is represented by the black line, relative to the right side vertical axis. The proportions of these isolates resistant to selected antibiotics in each year, excluding those for which no phenotype was available or that were defined as having an ‘intermediate’ resistance phenotype [see Additional file 1: Table S1], are represented by the coloured lines relative to the left side vertical axis. (C) Use of antibiotics in Iceland. Annual defined daily doses (DDD) in Iceland for classes of antibiotics against which IC1 isolates were found to have resistance are displayed. The data in panels (B) and (C) are plotted using the midpoint of each year such that they are displayed on approximately the same timescale as the changes in the effective population size of IC1 in panel (A).