Many types of pathogens can cause pneumonia, such as:
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Bacteria: Streptococcus pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae, Legionella pneumophila, and methicillin-resistant Staphylococcus aureus (MRSA)
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Viruses: Human rhinovirus, influenza A or B, coronavirus, and respiratory syncytial virus (RSV)
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Fungi: Pneumocystis jirovecii, Aspergillus spp., and Mucorales
The most prevalent causative microbes vary geographically. Viruses account for the majority of cases in children (<5 years)[1], whereas bacteria and viruses account for most cases of pneumonia in adults. Fungal pneumonia is quite rare and usually occurs in people who are immunocompromised (e.g., cancer patients).[2]
Pneumonia can also be caused by foods, liquids, or gastric contents inadvertently entering the lungs, a condition known as aspiration pneumonia.