Pneumonia can be caused by various infectious agents, including bacteria, viruses,
and fungi. The causative organisms can vary by age group and underlying health
conditions. Here's a list of some common pneumonia-causing organisms by age
group:
Infants and Newborns:





Respiratory Syncytial Virus (RSV)
Group B Streptococcus (GBS)
Chlamydia trachomatis
Streptococcus pneumoniae
Haemophilus influenzae
Children and Adolescents:





Streptococcus pneumoniae
Haemophilus influenzae
Mycoplasma pneumoniae
Chlamydophila pneumoniae
Respiratory viruses (e.g., influenza, adenovirus)
Young Adults (18-40):





Mycoplasma pneumoniae
Chlamydia pneumoniae
Streptococcus pneumoniae
Haemophilus influenzae
Respiratory viruses (especially in the winter)
Middle-Aged Adults (40-65):





Streptococcus pneumoniae
Haemophilus influenzae
Moraxella catarrhalis
Mycoplasma pneumoniae
Legionella pneumophila
Elderly Adults (65+):




Streptococcus pneumoniae
Haemophilus influenzae
Staphylococcus aureus
Klebsiella pneumoniae



Enterobacter spp.
Pseudomonas aeruginosa
Influenza and other respiratory viruses
Immunocompromised Individuals:

A wide range of organisms, including opportunistic pathogens, may cause
pneumonia in immunocompromised individuals. These can include bacteria
such as Staphylococcus aureus, Pseudomonas aeruginosa, and
Mycobacterium tuberculosis, as well as various fungal and viral pathogens.
It's important to note that the above list is not exhaustive, and the specific causative
organism can vary based on individual circumstances, geographic location, and
vaccination status. Additionally, the introduction of vaccines like the pneumococcal
vaccine has had a significant impact on reducing pneumonia cases caused by
Streptococcus pneumoniae in both children and adults. Proper diagnosis and
treatment are essential in managing pneumonia, and healthcare professionals will
consider a patient's age, health status, and other factors when determining the likely
causative agent.