Thoracic Empyema Due to Haemophilus parainfluenzae

Haemophilus parainfluenzae is thought to have lower pathogenicity than Haemophilus influenzae and is not a frequent cause of disease. To our knowledge, there is only 1 prior case of thoracic empyema caused by H. parainfluenzae. We report a second such case of a woman who developed a thoracic empyema due to H. parainfluenzae, although on methotrexate. It is probably safe to assume that immunosuppression is a risk factor for H. parainfluenzae infections. When isolated from the respiratory tract in symptomatic immunosuppressed patients, H. parainfluenzae should be considered a pathogenic organism. Increasing rates of ampicillin resistance, likely because of beta-lactamase production, suggest that quinolones should be the preferred first-line therapy.