INTRODUCTION: Pasteurella multocida is a gram-negative coccobacillus that often exists as a commensal in animals. It can cause a variety of infections in humans, usually associated with an animal bite or scratch. In this report, we describe a patient with lung cancer who developed empyema due to pasteurella, in the absence of an obvious animal exposure.
CASE PRESENTATION: A 67 year old white male, with a history of extensive stage small cell lung cancer, presented with a three day history of fever, dyspnea, dry cough and left sided pleuritic chest pain. He had received his second cycle of chemotherapy (carboplatin and etoposide) five days prior to presentation. His co-morbidities included coronary artery disease, abdominal aortic aneurysm and hypertension. He had a 40 pack year smoking history; he lived with his wife and had no pets at home. Subsequent history revealed that two weeks prior to presentation, he had visited a friend who owned a dog and he remembered briefly petting the animal. Examination was remarkable for decreased breath sounds, dullness to percussion and decreased tactile vocal fremitus in the left lung base. Labs showed leukopenia and anemia and chest X-ray revealed a new left sided pleural effusion and a stable left perihilar mass. The patient underwent a diagnostic thoracentesis which revealed an exudative effusion. Pleural fluid culture subsequently grew pasteurella multocida. The patient had a chest tube placed and was placed on appropriate antibiotics. His empyema resolved, the chest tube was removed and he was discharged home in good condition.
DISCUSSIONS: Pasteurella multocida is a small gram-negative bacterium that is part of the normal oral flora of many animals, including cats and dogs. It can cause a variety of infections in humans; generally, infections can be divided into three categories: 1) Soft tissue infections - the most common type and associated with animal bites/scratches 2) Oral and respiratory infections - acquired via inhalation of animal secretions 3) Serious invasive infections - e.g. meningitis, endocarditis, ocular infections that can be unrelated to animal bites. Infections of the respiratory tract with pasteurella are uncommon. Both the upper and lower respiratory tract can be involved. The most common pleuropulmonary infection is pneumonia, but pasteurella can cause pharyngitis, sinusitis, epiglottitis, tracheobronchitis, lung abscess and empyema. The majority of patients with pulmonary pasteurella multocida infections have an underlying condition, with chronic obstructive lung disease being the predominant illness. Other underlying conditions include malignancies, liver cirrhosis, and AIDS. Of note, in some of the reported cases of pulmonary infection with pasteurella, no known animal exposure was noted. In our patient, the brief contact with a dog was revealed only upon subsequent history. Diagnosis is via isolation of the organism on culture (e.g. sputum, blood, cerebrospinal fluid, pleural fluid, joint fluid). It is often missed due to a failure of keeping the organism in the differential diagnosis and due to misidentification on gram stained smear or inadequate laboratory identification techniques. Treatment is with antibiotics, and, depending on the site of infection, can entail debridement, drainage or irrigation.
CONCLUSION: Respiratory infections with pasteurella multocida are uncommon. They usually occur in the setting of preexisting lung disease or immunosuppression. Patients can acquire this infection with minimal animal exposure. A detailed exposure history is essential.
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