Identifying infectious etiologies of chronic disease.

Available information regarding possible infectious etiologies of insulin-dependent diabetes mellitus, rheumatoid arthritis, and systemic lupus erythematosus is reviewed. The problems and limitations of classic methods in trying to prove a causal relationship between an infectious agent and a chronic disease are summarized. The authors suggest that these disease occur as a result of persistent infection triggering an immunologic response (which is destructive of host tissue) in genetically susceptible individuals. Prospective studies within families (wherein individuals most at risk for disease can be identified) before the onset or diagnosis of the chronic disease may offer the best approach to elucidating potential infectious etiologies.