Which of the following infections is primarily caused by a virus?

Hepatitis refers to a viral infection that causes inflammation of the liver. It can be caused by several different viruses, including hepatitis A, hepatitis B, and hepatitis C. Each of these virus types has its own unique transmission methods, symptoms, and potential long-term effects.

Understanding the nature of hepatitis as a viral infection distinguishes it from the other options. For example, Escherichia coli is a type of bacteria that can cause gastrointestinal issues, Legionnaires' disease is caused by the Legionella bacteria and leads to a severe form of pneumonia, and Shigellosis is an infection primarily caused by bacteria of the Shigella genus, resulting in diarrhea. Each of these alternatives highlights bacterial rather than viral origins, making hepatitis the clear choice as the infection primarily caused by a virus.