This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Infection, Subject name: Medicine
[{'content': 'A 73-year-old man from a nursing home develops headache, fever, cough, sore throat, malaise, and severe myalgia during a community outbreak affecting numerous other residents at the home. The symptoms gradually resolve after 3 days, and he starts feeling better but then there is a reappearance of his fever, with cough and yellow sputum production. On examination, his temperature is 38.5degC, pulse 100/min, respiration 24/min, oxygen saturation 88% and crackles in the right lower lung base, bronchial breath sounds and dullness on percussion. CXR reveals a new infiltrate in the right lower lobe. Which of the following is the most likely causative organism? \nSelect and explain. \nA. primary viral pneumonia, B. an autoimmune reaction, C. Mycoplasma pneumoniae, D. Streptococcus pneumoniae', 'role': 'user'}, {'content': 'Answer: D \nExplanation: This man has a complication of viral influenza; a secondary bacterial pneumonia has developed. This usually occurs 2-3 days after the initial viral symptoms resolve. Primary viral pneumonia with influenza is not common. Spneumoniae, Staphylococcus, and H influenzae are the most common bacterial invaders in pulmonary complications of influenza. Pneumonia is the leading cause of death and may also be due to Spneumoniae and H influenzae. Mixed viral and bacterial pneumonia is common; pure viral pneumonia in influenza is uncommon (but can be very severe).', 'role': 'assistant'}]