Persistent <i>S. pneumoniae</i> strains causing ≥3 episodes of acute exacerbations in patients with chronic respiratory diseases.

a<p>S, susceptible (CPX MICs ≤2 mg/L); LL-R, low- level of resistance (MICs 4–8 mg/L); HL-R, high level of resistance (MICs ≥16 mg/L).</p>b<p><i>hol1</i> + indicates PCR detection for <i>hol1</i> gene; MitC + indicates cell lysis of the culture in the presence of MitC.</p>