Chapter 129: Lower Respiratory Tract Infections

Update Summary

May 25, 2023

The following section was updated:

• Minor edits were made to self-assessment questions to improve clarity.

KEY CONCEPTS

• Respiratory infections remain a major cause of morbidity from acute illness in the United States and represent the most common reasons why patients seek medical attention.

• The majority of pulmonary infections follow colonization of the upper respiratory tract with potential pathogens, whereas microbes less commonly gain access to the lungs via the bloodstream from an extrapulmonary source or by inhalation of infected aerosol particles. The competency of a patient’s immune status is an important factor influencing the susceptibility to infection, etiologic cause, and disease severity.

• An appropriate treatment regimen for a patient with uncomplicated lower respiratory tract infection can be established by evaluating the patient history, physical examination, chest radiograph, and properly collected sputum for culture interpreted in light of current knowledge of the most common lung pathogens and their antibiotic susceptibility patterns within the community.

• Acute bronchitis is most commonly caused by respiratory viruses and is almost always self-limiting. Therapy targets associated symptoms such as lethargy, malaise, or fever and may include fluids for rehydration. Routine use of antibiotics should be avoided and medication to suppress cough is rarely indicated.

• Chronic bronchitis is caused by several interacting factors, including inhalation of noxious agents (most prominent are cigarette smoke and exposure to occupational dusts, fumes, and environmental pollution) and host factors including genetic factors and bacterial (and possibly viral) infections. The hallmark of this disease is a chronic cough, accompanied by excessive production, and expectoration of sputum with a persistent presence of microorganisms in the patient’s sputum.

• Treatment of acute exacerbations of chronic bronchitis includes attempts to mobilize and enhance sputum expectoration (chest physiotherapy, humidification of inspired air), oxygen if needed, aerosolized bronchodilators in select patients with demonstrated benefit, and possibly antibiotics.

• Respiratory syncytial virus is the most common cause of acute bronchiolitis, an infection that mostly affects infants during their first year of life. In the well infant, bronchiolitis usually is a self-limiting viral illness.

• The most prominent pathogen causing community-acquired bacterial pneumonia in otherwise healthy adults is Streptococcus pneumoniae, whereas the most common pathogens causing hospital-acquired pneumonia are Staphylococcus aureus and gram-negative aerobic bacilli.

• Empiric antimicrobial therapy for pneumonia should consist of antibiotic regimens targeting presumed causative pathogens based on clinical presentation and patient-specific characteristics, local epidemiology, and resistance patterns.

• Microbiologic tests for pneumonia etiology should be performed when clinically indicated and used along with patient clinical response to tailor antibiotic therapy using evidence-based pathogen-directed therapy when possible.

BEYOND THE BOOK

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