SCIENCE SLEUTHS: THE SCIENCE THAT SHAPES DIAGNOSTIC TESTS
KOCH’S POSTULATES IN THE 21ST CENTURY In our recent piece entitled “Getting the target right – Germ Theory,” the concept of ‘germs’ as causative agents of disease was discussed. During the Golden Age of Microbiology, spanning the mid1800s to the start of the Great War in 1914, progress was made in leaps and bounds in the fields of science and medicine, and Germ Theory was born. This progress gave rise to modern concepts of hygiene, reduced mortality for new mothers, practices such as pasteurization and much more. Germ Theory was the foundation for Robert Koch’s Postulates of disease. The original postulates were: 1. The microorganism must be found in diseased animals [or humans] but not in healthy animals [or humans]. 2. The microorganism can be isolated from a diseased animal [or human]. 3. The isolated microorganism will cause disease if introduced into a healthy animal [or human]. 4. The microorganism must be able to be reisolated from the inoculated, diseased animal [or human] and identical to the original specific causative microorganism. In times where we can barely even imagine how few research tools these scientists had at their disposal, the need for rigor was paramount. Medical science was emerging from an era of empirical practices which included treatments with multiple, often spurious, ingredients and archaic practices with little evidence of
MARY MALLON, BETTER KNOWN AS TYPHOID MARY, LEFT, SITS AMONG A GROUP OF INMATES QUARANTINED ON AN ISOLATED ISLAND ON THE LONG ISLAND SOUND. PHOTOGRAPH: SCIENCE HISTORY IMAGES/ALAMY STOCK PHOTO.
efficacy such as bloodletting. Scientific rigor was the New Order. Koch’s postulates represented a central tenant of that new order and an evidence-based approach to medicine. As such, it will come as no surprise that most thinking, modern minds of the time embraced them and the medical profession has held them up as Gold Standards ever since. As brilliant and insightful as Koch’s postulates were even Koch himself recognized their shortcomings. For example, the agent of cholera, Vibrio cholerae, a source in intense interest and significant disease at the time, could easily found in sick patients, but could also be detected in some normal, healthy humans as well. This obviously did
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not fulfil postulate #1. The infamous case of Mary Mallon (1869 - 1938) is another rather sad example. Poor Mallon was an asymptomatic carrier of Salmonella typhi, typically the cause of typhoid fever. Working as a cook in the Northeast, she is believed to have infected 53 people with typhoid, of whom three died. It is from her that we get the colloquialism ‘Typhoid Mary.’ If someone talks about Typhoid Mary these days it’s often a euphemism for ‘a spreader of disease.’ To prevent Mallon from infecting more people, she was forcibly confined to a quarantine hospital on North Brother Island, New York, for the last 30 years of her life. Salmonella typhi is a significant
