Infections are caused by bacteria, viruses, fungi, or parasites. They’re spread by:
Exposure to coughs and sneezes of infected people
Contact with contaminated food, water, and surfaces
Contact with people who are infected, such as through kissing or sexual intercourse
Contact with creatures that are infected, such as pets, livestock, and insects, including fleas and ticks
Infections can lead to diseases, ranging from mild to severe, though less than 1% of bacteria actually cause disease in people.