that's a really fascinating question identification of African Sleeping Sickness is described but doesn't seem to have a formal case definition. But that's a much simpler disease - find type of germ: you have it. Similarly, bacterial meningitis describes looking for microbes but doesn't seem to have a formal case definition. Interestingly, they link to a WHO manual for techniques. Post-treatment Lyme Disease also links to external resources, these not from any type of government body. I also cannot find case definitions for diabetes (though that section is quite large so I could have missed in, and this would be taught in medical school so not too much need to go look it up), or Bovine Spongiform Encephalopathy (Mad Cow Disease, which would be less familiar even though likely covered in med school, so there would be a genuine need for HCP education). So yes, it doesn't seem to be necessary to have a case definition. It's just that CDC hosted the Fukuda (and maybe organized the International update) and supposedly operationalized it with Reeves 2005, and feels proud of their achievements.