The<unk>  or primary<unk>  is the initial patient in the population of an epidemiological investigation,
or more generally, the first<unk>  of a condition or syndrome (not necessarily contagious) to be described in the medical literature, whether or not the patient is thought to be the first person affected.[citation needed]
An<unk>  will sometimes achieve the status of a "classic"<unk>  in the literature, as did Phineas Gage.
The<unk>  may indicate the source of the disease, the possible spread, and which reservoir holds the disease in between outbreaks.  The<unk>  is the first patient that indicates the existence of an outbreak.  Earlier<unk> s may be found and are labeled primary, secondary, tertiary, etc. "Patient Zero" was used to refer to the<unk>  in the spread of HIV in North America.
In genetics, the<unk>  is the<unk>  of the original patient (propositus or proband) that stimulates investigation of other members of the family to discover a possible genetic factor.
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Bedwetting epidemiology and demographics
Risk factor template
Biased sample
Clinical trials terminology
Cumulative incidence
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Clinical ecology