Aggregatibacter aphrophilus in a patient with recurrent empyema: a case report

INTRODUCTION: Aggregatibacter aphrophilus (formerly Haemophilus aphrophilus and H. paraphrophilus) is classically associated with infective endocarditis. Other infections reported in the literature include brain abscess, bone and joint infections and endophthalmitis. There are only two cases of empyema ever reported due to this organism. We report the isolation of A. aphrophilus from pleural fluid on three separate hospital admissions in a patient with recurrent empyema. CASE PRESENTATION: A 65-year-old female patient of Caucasian origin presented with a three-week history of fever, shortness of breath and dry cough. She was found to have a pleural empyema so a chest drain was inserted and a sample of pus was sent to the microbiology laboratory. After overnight incubation, a chocolate blood agar plate incubated in 5% carbon dioxide showed a profuse growth of small, round, glistening colonies which were identified as Gram-negative coccobacilli. They were oxidase- and catalase-negative. Biochemical testing using RapID NH confirmed the identity of the organism as A. aphrophilus. It was susceptible to amoxicillin, levofloxacin and doxycycline. Our patient was treated with intravenous amoxicillin with clavulanic acid and clarithromycin followed by oral doxycycline, but was re-admitted twice over the next three months with recurrent empyema and the same organism was isolated. Each episode was managed with chest drainage and a six-week course of antibiotic--doxycycline for the second episode and amoxicillin for the third episode, after which she has remained well. CONCLUSION: This is the first case report of recurrent empyema due to A. aphrophilus. Our patient had no underlying condition to explain the recurrence. Although our isolate was doxycycline susceptible, our patient had recurrent infection after treatment with this antibiotic, suggesting that this antibiotic is ineffective in treatment of deep-seated A. aphrophilus infection. This organism can be difficult to identify in the laboratory because, unlike closely related Haemophilus spp., it is oxidase-negative, catalase-negative and X and V independent.