Get 9 hours of sleep each night, eat a balanced diet with 5 or 3 meals per day, and wash hands and shower daily to maintain good hygiene. Infectious illnesses are caused by bacteria or viruses, with bacteria being unicellular microorganisms that can be beneficial like in yogurt or harmful and cause sickness, and viruses needing host cells to survive and not being considered living themselves. Vaccines can prevent some illnesses while antibiotics treat bacterial infections.