Pneumonia in children can be a bacterial infection, a viral infection, or a mixed bacterial, viral, and mycoplasma infection. There are many pathogens that cause pneumonia in children, including viruses, bacteria, mycoplasma, chlamydia, rickettsia, protozoa, and fungi, with viral and bacterial infections being the most common. It is usually possible to determine roughly whether the infection is viral or bacterial based on routine blood, C-reactive protein, serum amyloid, etc. The extent and degree of inflammation in the lungs can be known by X-ray examination. In the case of hospitalized patients, serum antibodies, bacterial cultures, nucleic acid testing of viruses, and PCR of pharyngeal swabs can be used to clarify exactly which pathogenic infection is causing the infection, and bacteria can also be tested for drug sensitivity, which can guide clinical antibiotic use.