Also known as healthcare-associated infections (HAI), are infections that occurs in healthcare settings. Sick patients can bring harmful pathogens into hospitals, and some of these pathogens can be transmitted easily via improperly sterilized medical equipment, door handles, or by clinicians who do not wash their hands between patients. Hospital patients often have weakened immune systems, making them more susceptible to infections. Infections are classified as HAI when the patient was admitted for another reason (primary disease) than the infection, and then, often, contracts the secondary infection after having compromised immunity (such as due to surgery).