Which pathogen is most commonly associated with community-acquired pneumonia (CAP)?

Streptococcus pneumoniae is the most frequently identified pathogen in cases of community-acquired pneumonia (CAP). This bacterium is known for its significant role in both community and hospital settings, primarily affecting children and older adults.

The reason S. pneumoniae is associated with CAP lies in its prevalence in the general population. It is often found in the upper respiratory tract of healthy individuals, which means it can easily spread to the lower respiratory tract and cause pneumonia, particularly in those with predisposing factors such as age, chronic illnesses, or compromised immunity.

While other pathogens like Haemophilus influenzae, Mycoplasma pneumoniae, and Legionella pneumophila can also cause pneumonia, they are less commonly seen as primary pathogens in uncomplicated cases of CAP. H. influenzae is more frequently associated with exacerbations of chronic pulmonary conditions. Mycoplasma pneumoniae is often implicated in atypical pneumonia, particularly among younger populations, and tends to present with milder symptoms. Legionella pneumophila, while associated with pneumonia, is more likely to be found in outbreaks and is associated with specific environmental exposures, making it less common in the general community setting.

Thus, the dominance of Streptococcus pneumoniae as a causative