Clinical characteristics of pneumonia caused by beta-lactamase negative ampicillin resistant Haemophilus influenzae (BLNAR).

We wished to assess the clinical differences between beta-lactamase-negative, ampicillin-sensitive and beta-lactamase-negative, ampicillin-resistant Haemophilus influenzae pneumonia. The medical records of 118 patients with H. influenzae pneumonia admitted between March 1998 and March 2003 to Nagasaki University Hospital and affiliated institutions were reviewed. In line with CLSI (Clinical and Laboratory Standards Institute) criteria, we classified H. influenzae according to sensitivity to ampicillin as follows: S (sensitive), minimum inhibitory concentration (MIC) =1; I (intermediate sensitivity), MIC =2; R (resistant), MIC =4. We defined the R strains as the BLNAR group and the S and I strains as the non-BLNAR group. We measured the patient's background, Pneumonia Severity Index (PSI), drug sensitivity of H. influenzae, and evaluation of antibiotic choices. There were no significant clinical differences between the beta-lactamase-negative, ampicillin-susceptible and the beta-lactamase-negative, ampicillin-resistant groups. However, BLNAR pneumonia was more prominent in the younger than the older patients. This study should provide useful information for understanding the clinical characteristics of BLNAR pneumonia.