It is difficult to discover the cause of a chronic disease that evolves over decades, and over the evolution of the disease the symptom progression has been given many different names. Research is limited in discovery of the causes of chronic diseases, because it is limited to one guess, one hypothesis, one consistent finding, one point in time, and one publication. Research has been limited by the one cause per disease theory, which limited a broader understanding about infectious causes and co-infectious causes of chronic disease. Research funding into infectious causes has been a small fraction of research funding into alternative hypotheses, symptomatic treatment, and novel therapies.
Discovery of the cause of chronic diseases that evolve over a long period of time requires a systematic review of retrospective studies (as was done in cardiac disease, and some other fields); prospective studies on the causes suggested by retrospective studies; a deep dive into the medical history and prior medical treatment of the patient; and clinical trials that include an extensive medical history, and the diagnosis and treatment of pathogens found. If a drug is known to treat specific pathogens, the patient is shown to harbor the pathogens, the patient takes the drug and the chronic disease improves, it is a beginning of understanding the origin of chronic disease.