A 68-year-old woman comes to the emergency department due to cough and shortness of breath. She has a history of chronic obstructive pulmonary disease and often coughs up clear sputum in the morning. Over the past 4 days, the cough has worsened significantly, and the patient now is producing thick, greenish sputum. She also feels winded when walking short distances or doing light housework. She is a former smoker with a 40-pack-year history. Temperature is 37.2 C (99 F), blood pressure is 130/70 mm Hg, pulse is 90/min, and respirations are 22/min. The patient is breathing with pursed lips. The expiration phase is prolonged. Vesicular breath sounds with diffuse wheezes are heard on lung auscultation. Chest x-ray shows hyperinflated lungs with a flattened diaphragm. There are no alveolar opacities or pleural effusions. Respiratory viral panel results are negative. Infection with which of the following pathogens most likely triggered this patient's worsening symptoms?
Acute exacerbation of chronic obstructive pulmonary disease | |
Precipitants |
|
Pathophysiology & presentation |
|
Management |
|
*For example, spontaneous sterile inflammation (underlying disease), pulmonary embolism, inhaled irritants. **In some cases, acute exacerbation of chronic obstructive pulmonary disease is precipitated by community-acquired pneumonia (alveolar opacities, fever, or leukocytosis). RSV = respiratory syncytial virus; V/Q = ventilation/perfusion. | |
This patient with a history of chronic obstructive pulmonary disease (COPD) has increasing dyspnea and purulent sputum production consistent with an acute exacerbation (AECOPD). Precipitants of AECOPD can be divided into infectious and noninfectious causes. Infectious etiologies account for roughly two-thirds of all cases of AECOPD:
The 3 bacteria most commonly isolated during AECOPD are nontypeable Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae.
The 3 most common viral triggers of AECOPD are human rhinovirus, influenza, and respiratory syncytial virus.
Infection results in direct damage to respiratory ciliated epithelium, cytokine-mediated airway inflammation, and mucus hypersecretion, all of which worsen the baseline symptoms of COPD. The presence of purulent (eg, greenish, malodorous) sputum merely denotes the influx of activated neutrophils (myeloperoxidase produces the green hue) and does not reliably distinguish between viral or bacterial infection.
(Choice A) Bordetella pertussis causes whooping cough, which is characterized by extremely severe, paroxysmal, nonproductive cough. Although vaccinated adults can have an attenuated form of pertussis, it preferentially affects the trachea (rather than the lower bronchi) and is therefore a rare cause of AECOPD.
(Choices C and D) Klebsiella pneumoniae and Legionella pneumophila are important causes of nosocomial (health care–associated) pneumonia but can also cause community-acquired pneumonia in susceptible individuals (eg, alcohol use disorder, immunosuppression). In both cases, alveolar opacification would be expected on chest x-ray. Klebsiella pneumonia is characterized by hemorrhagic lung necrosis (currant-jelly sputum) and early abscess formation. Legionella pneumonia is characterized by pulmonary symptoms and a febrile gastroenteritis.
(Choice E) Staphylococcus aureus is a common cause of postviral (eg, postinfluenza) pneumonia but a very uncommon cause of AECOPD. It presents with alveolar opacification on x-ray accompanied by a severe systemic inflammatory response (fever, leukocytosis, hypotension). Overgrowth of S aureus within the airways of patients with cystic fibrosis can induce acute exacerbations of bronchiectasis.
(Choice F) Streptococcus pyogenes is a common cause of acute bacterial pharyngitis (strep throat) but does not usually affect the airways to cause a COPD exacerbation.
Educational objective:
Viral and bacterial respiratory infections are the leading cause of acute exacerbations of chronic obstructive pulmonary disease. The most common bacterial pathogens include nontypeable Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis.