A
subclinical infection (sometimes called a
preinfection) is an
infection that, being , is nearly or completely asymptomatic (no
signs or
symptoms). A subclinically infected person is thus an
asymptomatic carrier of a
microbe,
intestinal parasite, or
virus that usually is a
pathogen causing
illness, at least in some individuals. Many pathogens spread by being silently carried in this way by some of their
host population. Such infections occur both in humans and nonhuman animals. An example of an asymptomatic infection is a mild
common cold that is not noticed by the infected individual. Since subclinical infections often occur without eventual overt sign, their existence is only identified by
microbiological culture or DNA techniques such as
polymerase chain reaction.