Bacteria and viruses are too tiny to be seen by the naked eye, can cause similar symptoms and are often spread in the same way, but that's where the similarities end.
A bacterium is a single, but complex, cell. It can survive on its own, inside or outside the body. Most bacteria aren't harmful. In fact, we have many bacteria on and inside our body, especially in the gut to help digest food.
Viruses are smaller and are not cells. Unlike bacteria, they need a host such as a human or animal to multiply. Viruses cause infections by entering and multiplying inside the host's healthy cells.
Read more at: https://www.healthdirect.gov.au/bacterial-vs-viral-infection