Complex sentence: The primary infection is most commonly by bacteria, but can also be by fungi, viruses, or parasites, and can be located in any part of the body, but most commonly in the lungs, brain, urinary tract, skin, or abdominal organs.
Split into simpler sentences: The primary infection is most commonly by bacteria, but also may be by fungi, viruses, or parasites. It may be located in any part of the body, but most commonly in the lungs, brain, urinary tract, skin, or abdominal organs.