Are lung infections commonly contagious?

Yes: But they are not highly contagious. The infections are transmitted by droplets containing bacteria. However the host usually needs to have some type of increased susceptibility in order to get the infection.

Yes and No: Some lung infections or pneumonias such as viral, influenza and bacterial, tuberculosis are contageous from person to person. Other pneumonias such as aspiration pneumonia or ventilator associated pneumonias are not contageous.

No: Most viruses are contagious, but very few bacterial lung infections are actually transmitted from person to person. The one major exception to this is tuberculosis. Bacterial infections usually happen with bacteria which already colonize our body.