What is the primary pathogen responsible for community-acquired pneumonia?

Streptococcus pneumoniae is the primary pathogen responsible for community-acquired pneumonia (CAP). This bacterium is a common inhabitant of the nasopharynx and can cause a range of illnesses, especially in individuals with underlying health conditions or weakened immune systems.

Streptococcus pneumoniae is well-recognized for causing both acute and chronic infections. In the context of pneumonia, it leads to significant inflammation and fluid accumulation in the alveoli, which is characteristic of pneumonia. This pathogen is particularly prevalent in the elderly and in young children, populations that are at higher risk for pneumonia-related complications.

While other pathogens listed can cause community-acquired pneumonia, they occur less frequently or are associated with different patient demographics or more atypical presentations. For example, Staphylococcus aureus is more often linked to healthcare-associated pneumonia or specific circumstances like post-influenza pneumonia. Haemophilus influenzae can cause respiratory issues, primarily in those with chronic lung diseases or in children, while Mycoplasma pneumoniae typically causes a milder, atypical form of pneumonia more common in young adults and adolescents, rather than the predominant type seen in broader community settings. Thus, Streptococcus pneumoniae remains the leading cause of CAP due to