Co-morbid diseases should be investigated for possible common infectious causes or combinations of infectious causes.  A history of acute infections in the patient, family, household animals, and community is necessary, as the triggering acute infectious event may have occurred years or decades before the onset of chronic disease. Co-morbid diseases may be an observation of different stages and/or processes in the evolution of acute disease into chronic disease; and often may be explained by starting with the known effects of specific infectious pathogens, and reasoning how over time the known effects could cause a chronic disease and the co-morbid conditions.

Co-morbid diseases may be described in each specialty and/or disease literature as having the same “association” with infectious causes; yet, the limited crossover in care and knowledge of infectious causes between specialties, and the limited communication between specialties, limits recognition of potential common origins. The cause of chronic diseases will seldom be found in one specialty alone. Finding the causes of chronic disease will require collaboration between specialties and a longer and broader view of chronic disease.