A 67-year-old man is brought to the emergency department by his wife due to 1 day of worsening fever, chills, productive cough, shortness of breath, and confusion. Five days ago, the patient was diagnosed with influenza. He initially improved but "took a turn for the worse" yesterday. His medical history includes hypertension and osteoarthritis. He smokes half a pack of cigarettes daily and drinks alcohol several times a week. Temperature is 40.5 C (105 F), blood pressure is 95/60 mm Hg, pulse is 106/min, and respirations are 24/min. Pulse oximetry is 90% on room air. Cardiac examination is normal, with the exception of tachycardia. Lung auscultation shows right-sided crackles and bronchial breath sounds. Chest x-ray is shown below. Which of the following is the infectious agent most likely responsible for this patient's condition?

Question

A 67-year-old man is brought to the emergency department by his wife due to 1 day of worsening fever, chills, productive cough, shortness of breath, and confusion.  Five days ago, the patient was diagnosed with influenza.  He initially improved but "took a turn for the worse" yesterday.  His medical history includes hypertension and osteoarthritis.  He smokes half a pack of cigarettes daily and drinks alcohol several times a week.  Temperature is 40.5 C (105 F), blood pressure is 95/60 mm Hg, pulse is 106/min, and respirations are 24/min.  Pulse oximetry is 90% on room air.  Cardiac examination is normal, with the exception of tachycardia.  Lung auscultation shows right-sided crackles and bronchial breath sounds.  Chest x-ray is shown below.  Which of the following is the infectious agent most likely responsible for this patient's condition?

Quizplus · Accepted Answer

11ec25c8_d445_4925_bc81_fb6c686dd188_MD0003_00 Secondary bacterial pneumonia is the most common complication of influenza and should be suspected in any patient who develops worsening fever and pulmonary symptoms (eg, dyspnea, productive cough) after initial symptomatic improvement. Patients >65 and with certain comorbid conditions (eg, immunosuppression, lung disease) are at greatest risk. Streptococcus pneumoniae and Staphylococcus aureus are the 2 most common etiologic organisms. S aureus pneumonia tends to be severe, necrotizing, and rapidly progressive. Patients often have high fever, hypotension, dyspnea, hemoptysis, and confusion. Chest x-ray may reveal lobar or multilobar infiltrates with or without cavitation. Blood and sputum cultures are usually obtained but have low sensitivity (likely due to poor sputum sampling and intermittent bacteremia). Patients usually require treatment in the intensive care unit and are often started on multiple broad-spectrum, empiric antibiotics (eg, vancomycin, piperacillin-tazobactam, and levofloxacin). Mortality is as high as 55%. (Choices A and C) Klebsiella pneumoniae and mixed anaerobes often cause pulmonary infections in those at risk for aspiration (eg, alcoholism). Symptoms of putrid sputum and infiltrates in the dependent pulmonary lobes (right lower, right middle) are common. Although this patient uses alcohol several times a week, pulmonary infection 5 days after influenza is much more likely to be caused by S pneumoniae or S aureus. (Choice B) Legionella typically causes high fever and prominent gastrointestinal symptoms (vomiting, diarrhea), with symptoms of community-acquired pneumonia evolving slowly. This patient has acute pulmonary symptoms and no gastrointestinal symptoms, making Legionella less likely. (Choice D) Mycoplasma pneumoniae usually causes indolent (not acute) symptoms of headache, malaise, nonproductive cough, and low-grade fever. (Choice E) Pseudomonas aeruginosa typically causes nosocomial pneumonia. S pneumoniae and S aureus would be far more likely after influenza in the community setting. Educational objective: Secondary bacterial pneumonia is the most common complication of influenza and should be suspected in any patient who develops worsening fever or pulmonary symptoms after initial improvement. Streptococcus pneumoniae and Staphylococcus aureus are the most common etiologic organisms. S aureus pneumonia tends to cause rapid-onset, severe, necrotizing pneumonia with high risk of death.

A 67-Year-Old Man Is Brought to the Emergency Department by His