Community-acquired pneumonia is the presence of signs and symptoms of lower respiratory tract infection acquired outside of the hospital.
The most common bacterial cause of childhood pneumonia is Streptococcus pneumoniae. It usually causes about 1/3 of radiographically-confirmed pneumonia in children <2 years of age.
Viruses commonly affect children <1 year of age than those aged >2 years, respiratory syncytial viruses (RSV) being the most frequently detected virus.
Mixed infection may occur in 8-40% of community-acquired pneumonia cases.