Discussion
RESPIRATORY TRACT INFECTIONS, COMMUNITY-ACQUIRED PNEUMONIA
We observed a discrepancy in azithromycin susceptibility depending on whether using breakpoints from EUCAST or CLSI guidelines for interpretation. All 13 PNSP isolates harboring genetic determinants for macrolide resistance were correctly identified as resistant to erythromycin and azithromycin (all with MIC ≥ 4 µg/mL) regardless of which breakpoints were used (sensitivity 100%, 13/13). Using the EUCAST breakpoints appeared to overestimate azithromycin resistance, as all 13 erythromycin-susceptible PNSP without genetic determinants of macrolide resistance were interpreted as resistant to azithromycin (MIC-values from 0.5 to 2, specificity 0%, 0/13). Using CLSI breakpoints only misclassified two such isolates (MIC 2 µg/mL, specificity 85%, 11/13). Therefore, relying on current EUCAST guidelines appears to overestimate azithromycin resistance and could in the clinical perspective lead to unnecessary use of more broad-spectrum antibiotics. Our findings suggest that the EUCAST guidelines currently use a too low cutoff for MIC-values for azithromycin resistance in pneumococci.PNSP susceptibility to erythromycin, on the other hand, was similar using both EUCAST and CLSI breakpoints, and the phenotypic findings correlated well with the identified genotypic resistance markers. To avoid variations in interpretation, our findings call for AST guidelines to be harmonized. Both CLSI and EUCAST state that erythromycin susceptibility can predict susceptibility to clarithromycin, azithromycin, dirithromycin, and roxithromycin [In Tanzania, macrolides are commonly used to treat respiratory tract infections. In the treatment of community-acquired pneumonia, erythromycin and azithromycin are used as first and second line treatment, respectively [The most common phenotype was MLSPrevious studies have shown that tetracycline and macrolide resistance genes are carried on mobile genetic elements, composite conjugative transposons, Tn