system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does a doctor differentiate walking pneumonia from bronchitis, the flu, or MONO?
gpt
Bacterial pneumonia (both typical and walking) is diagnosed through a sputum culture. The patient coughs up fluid from the airways, and the sample is incubated. If there's bacteria in the sample, they will grow and form cultures. The bacterium can be identified using microscopy or special biochemical tests.

Viral pneumonia (including influenza) is diagnosed through PCR, a type of genetic test. It detects viral DNA.

Bronchitis is diagnosed through a spirometry, a type of breathing test. It tests how much air the patient can exhale in 1 second. This number is reduced in bronchitis, COPD and asthma.