Background:

Bacillus cereus (B. cereus) rarely causes lower respiratory tract infections, although most reported cases of B. cereus pneumonia are fatal despite intensive antibiotic therapy. We present a case of B. cereus pneumonia in an immunocompetent patient.
Case presentation:
An 81-year-old woman was transferred from a district general hospital to our hospital for treatment of congestive heart failure. The patient presented with a nonproductive cough, dyspnea, edema in both lower extremities, orthopnea, fever, and occult blood in the stool. A chest radiograph indicated bilateral pleural effusion and pulmonary congestion. After diuretic therapy and chest drainage, bilateral pleural effusion and pulmonary congestion improved. On day 2, she experienced severe respiratory distress. B. cereus was isolated from two blood sample cultures. On day 4, her condition had progressed to severe respiratory distress (PaO2/FiO2 ratio = 108). A chest radiograph and computed tomography indicated extensive bilateral infiltrates. She was transferred to the intensive care unit and was intubated. B. cereus was also isolated from five blood sample cultures at that time. After isolating B. cereus, we switched antibiotics to a combination of imipenem and levofloxacin, which were effective. She had no history of immunodeficiency, surgery, ill close contacts, risk factors for HIV or tuberculosis, recent central venous catheter insertion, or anthrax vaccination. She improved and was discharged from the intensive care unit after several days.
Conclusion:
This is a rare case of B. cereus pneumonia in an immunocompetent patient, who subsequently recovered. Bacillus should be considered as a potential pathogen when immunocompetent patients develop severe pneumonia.