News FocusInfectious Disease

19th Century Rules of Causation Outdated?

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Science  09 Oct 1998:
Vol. 282, Issue 5387, pp. 220
DOI: 10.1126/science.282.5387.220

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German microbiologist Robert Koch argued in 1890 that to prove an organism causes a disease, microbiologists must show that the organism occurs in every case of the disease; that it is never found as a harmless parasite associated with another disease; and that once the organism is isolated from the body and grown in laboratory culture, it can be introduced into a new host and produce the disease again. But Koch's criteria are now being swept aside by molecular techniques that pull segments of microbe DNA or RNA directly out of infected tissues.