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Table 1 Zone diameter interpretive standards and equivalent MIC breakpoints for H. influenzae and H. parainfluenzae

From: No development of ciprofloxacin resistance in the Haemophilus species associated with pneumonia over a 10-year study

  CLSI 2004–2011 EUCAST 2012–2014
MIC breakpoints (μg/mL) Disk content (μg) Zone diameter breakpoint (mm) MIC breakpoints (mg/dL) Disk content (μg) Zone diameter breakpoint (mm)
Antibiotic Sensitive ≤ Resistant ≥ Sensitive ≤ Resistant >
Sensitive ≥ Resistant ≤   Sensitive ≥
Ampicillin 1 4 10 22 18 1 1 2 18
Piperacillin 1 4 10 22 18 1 1 2 18
Ampicillin + Sulbactam 2 2 10 + 10 20 19 1 1 10 + 10 Not available
Piperacillin + Sulbactam 1 2 10 + 10 20 19 2 2 10 + 10 Not available
Piperacillin + Tazobactam 1 2 100 + 10 21 2 2 Susceptibility inferred from ampicillin susceptibility
Cefuroxime 4 16 30 20 16 1 2 5 17
Cefotaxime 2 30 26 0.125 0.125 5 25
Ciprofloxacin 1 5 21 0.5 0.5 1 28
Levofloxacin 2 5 17 1 1 1 26
Erythromycin 0.5 16 5 50