NIH Module 7 – Laboratory Testing, Diagnostic Imaging, and Screening Practice Test

External-source infections are called exogenous infections. The defining idea is that the pathogen comes from outside the body and enters through routes like inhalation of environmental organisms, ingestion of contaminated food or water, direct contact with an infected person, or through a contaminated medical device, and then establishes infection. This contrasts with endogenous infections, which arise from microorganisms that normally reside in or on the body and cause disease only after they gain access to sterile sites or after disruption of the usual barriers. A carrier is someone who harbors the pathogen without symptoms but can spread it, and a subclinical case is an infection that remains asymptomatic despite the presence of the pathogen. An example of an exogenous infection is acquiring a pathogen from a contaminated instrument or environment in a healthcare setting.