Respiratory Bacterial Infections

Respiratory bacterial infections are infections of the airways and lung parenchyma caused by bacteria, spanning the upper tract (such as bacterial pharyngitis and sinusitis) and, with greater clinical weight, the lower tract, where bacterial pneumonia and bronchitis arise. Community-acquired pneumonia is the prototypical and most consequential syndrome in this group.

Definition

A respiratory bacterial infection is an infection of the upper or lower respiratory tract in which bacteria invade and multiply in the airway mucosa or lung parenchyma, producing inflammation and the clinical syndrome of pneumonia, bronchitis, or upper-airway infection.

Scope

The entry covers the bacterial infections of the respiratory tract as a clinical entity, with emphasis on the lower-tract syndromes (pneumonia and acute bronchitis) that carry the greatest burden, the common bacterial causes, and the host and epidemiological factors that shape presentation. It is a reference overview and does not provide antibiotic regimens or individualized care.

Core questions

• Is the infection in the upper or lower respiratory tract, and what syndrome does it produce?
• Which bacteria are the typical causes, and how does the setting (community versus hospital) change the likely pathogens?
• How do host factors such as age, comorbidity, and immune status affect severity?
• How is the severity of pneumonia assessed for prognosis?

Key concepts

• Upper versus lower respiratory tract infection
• Community-acquired pneumonia
• Hospital-acquired and ventilator-associated pneumonia
• Acute bronchitis
• Typical versus atypical bacterial pathogens
• Streptococcus pneumoniae as a leading cause
• Severity assessment and prognosis

Mechanisms

Lower respiratory bacterial infection typically follows aspiration of colonizing oropharyngeal flora or inhalation of aerosolized organisms that reach the distal airways and alveoli, where they overwhelm local defenses and provoke an inflammatory exudate that fills the alveolar spaces. The resulting consolidation impairs gas exchange and produces the cough, fever, and dyspnea of pneumonia. The likely organism depends on where the infection was acquired: Streptococcus pneumoniae and other typical and atypical bacteria dominate in the community, while hospital- and ventilator-associated pneumonia involves a different and often more resistant spectrum (Prina, 2015).

Clinical relevance

Respiratory bacterial infections, and pneumonia in particular, are among the most common reasons for infection-related illness and hospitalization, and severity assessment helps determine prognosis and level of care. This entry describes how these syndromes are categorized and reasoned about as a reference; it is not a basis for prescribing or for individual management decisions.

Epidemiology

Community-acquired pneumonia is a leading infectious cause of morbidity and hospitalization worldwide, with incidence highest at the extremes of age and in people with chronic lung, heart, or immune conditions (Prina, 2015). Lower respiratory infections are also a major contributor to deaths attributable to bacterial antimicrobial resistance, reflecting the prominence of pathogens such as Streptococcus pneumoniae and Klebsiella pneumoniae (Murray, 2022).

History

The bacterial causation of pneumonia was established in the late nineteenth century with the identification of the pneumococcus, and the disease was a leading cause of death before antibiotics. Pneumococcal and Haemophilus influenzae type b conjugate vaccines later reduced the burden of several respiratory bacterial infections, while resistance among respiratory pathogens has become a continuing concern (Murray, 2022).

Seminal works

• prina-2015
• bradley-2011

Frequently asked questions

What is the most common bacterial cause of community-acquired pneumonia?

Streptococcus pneumoniae (the pneumococcus) is the most frequently identified bacterial cause of community-acquired pneumonia, although atypical bacteria and other organisms also contribute and many cases have no identified pathogen.

How do community-acquired and hospital-acquired pneumonia differ?

They differ mainly in the spectrum of likely organisms and resistance: community-acquired pneumonia is dominated by pathogens such as the pneumococcus, whereas hospital-acquired and ventilator-associated pneumonia more often involve resistant Gram-negative bacteria and Staphylococcus aureus.