Antimicrobial Resistance Among Haemophilus influenzae Isolates

We read with interest the article by Jorgensen on antimicrobial resistance among isolates of Haemophilus influenzae. Over a 6-month period (July through December 1992), we observed four acutely ill trauma patients in our intensive care unit whose isolates of H. influenzae were initially susceptible to ampicillin but were subsequently resistant to this antibiotic. This resistance occurred over 2-10 days and became clinically significant. Each of these patients was treated with ampicillin for either bronchitis or pneumonia caused by a beta -lactamase negative isolate of H. influenzae. Although the conditions of each of our four patients initially improved over the first 48-72 hours, their respiratory status clinically deteriorated because of increased fever, hypoxemia, and worsening pulmonary infiltrates. Repeated tests for beta -lactamase production were positive, indicating the Haemophilus isolates were now ampicillin resistant.