The Fault of Viruses
As you might’ve noticed, viruses—or at least a strain of a specific virus—are responsible for all three. Colds are usually caused by rhinovirus strains. Influenza has 3 types and multiple sub-types. Pneumonia, however, can be caused by either a virus or a bacterial infection. Viral pneumonia doesn’t last as long as the bacterial type and is also far less severe.
