A 71-year-old woman is admitted to the hospital for pneumonia. The patient presented to the hospital 2 days ago for cough and fever. She reported temperatures to 38.9 C (102 F) and a cough productive of green, copious sputum. She also reported pleuritic chest pain with deep inspiration. The initial examination revealed diminished breath sounds in the left lower lobe with dullness to percussion, and a chest radiograph revealed a dense left lower lobe infiltrate. Which of the following organisms is most likely responsible for her pneumonia?
A. Bordetella pertussis
B. Klebsiella pneumoniae
C. Mycoplasma pneumoniae
E. Staphylococcus aureus
The correct answer is
D. The etiology of pneumonia is related to both the age of the patient and the particular risk factors that he or she may exhibit. For patients with no specific risk factors, pneumonia is referred to as community-acquired pneumonia (CAP). CAP has a variable etiology depending on the age of the patient. In patients aged 29-55, the pneumococcus (Streptococcus pneumoniae), a gram-positive organism, is the most frequent agent causing so-called typical or bacterial pneumonia.
Bordetella pertussis(choice A) causes whooping cough in children. Most adults in the U. S. have been vaccinated against this organism. However, 20 years after the last booster, immunity begins to fade, and it is reasonably common to see patients aged 55 and older presenting with upper and lower respiratory tract infections caused by this organism.
Klebsiella pneumoniae(choice B) is a reasonably frequent source of pneumonia in both hospitalized patients and those with chronic aspiration problems, such as post-stroke patients.
Mycoplasma pneumoniae(choice C) is the primary agent responsible for so-called atypical pneumonia in the same age bracket.
Staphylococcus aureus(choice E) is a gram-positive organism that causes severe cavitating pneumonia. It is most often responsible for pneumonia in diabetic patients.