Editing Infection (section)

====Infectious or not====
One manner of proving that a given disease is infectious, is to satisfy [[Koch's postulates]] (first proposed by [[Robert Koch]]), which require that first, the [[infectious agent]] be identifiable only in patients who have the disease, and not in healthy controls, and second, that patients who contract the infectious agent also develop the disease. These postulates were first used in the discovery that [[Mycobacteria]] species cause [[tuberculosis]].<ref name="pmid28515626">{{cite journal |vauthors=Barberis I, Bragazzi NL, Galluzzo L, Martini M |title=The history of tuberculosis: from the first historical records to the isolation of Koch's bacillus |journal=Journal of Preventive Medicine and Hygiene |volume=58 |issue=1 |pages=E9–E12 |date=March 2017 |pmid=28515626 |pmc=5432783 |doi= |url=}}</ref>

However, Koch's postulates cannot usually be tested in modern practice for ethical reasons. Proving them would require experimental infection of a healthy individual with a [[pathogen]] produced as a pure culture. Conversely, even clearly infectious diseases do not always meet the infectious criteria; for example, ''[[Treponema pallidum]]'', the causative [[spirochete]] of [[syphilis]], cannot be [[microbiological culture|cultured]] ''in vitro'' – however the organism can be cultured in rabbit [[testes]]. It is less clear that a pure culture comes from an animal source serving as host than it is when derived from microbes derived from plate culture.<ref name="pmid31440916">{{cite journal |vauthors=Hosainzadegan H, Khalilov R, Gholizadeh P |title=The necessity to revise Koch's postulates and its application to infectious and non-infectious diseases: a mini-review |journal=European Journal of Clinical Microbiology & Infectious Diseases|volume=39 |issue=2 |pages=215–218 |date=February 2020 |pmid=31440916 |doi=10.1007/s10096-019-03681-1 |s2cid=201283277 |url=}}</ref>

[[Epidemiology]], or the study and analysis of who, why and where disease occurs, and what determines whether various populations have a disease, is another important tool used to understand infectious disease. Epidemiologists may determine differences among groups within a population, such as whether certain age groups have a greater or lesser rate of infection; whether groups living in different neighborhoods are more likely to be infected; and by other factors, such as gender and race. Researchers also may assess whether a disease [[outbreak]] is sporadic, or just an occasional occurrence; [[endemic (epidemiology)|endemic]], with a steady level of regular cases occurring in a region; [[epidemic]], with a fast arising, and unusually high number of cases in a region; or [[pandemic]], which is a global epidemic. If the cause of the infectious disease is unknown, epidemiology can be used to assist with tracking down the sources of infection.<ref name="pmid31325286">{{cite journal |vauthors=Riley LW |title=Differentiating Epidemic from Endemic or Sporadic Infectious Disease Occurrence |doi-access=free |s2cid-access=free |journal=Microbiology Spectrum |volume=7 |issue=4 |pages= |date=July 2019 |pmid=31325286 |doi=10.1128/microbiolspec.AME-0007-2019 |s2cid=198135563 |url=|pmc=10957193 }}</ref>