The association between tuberculosis and diphtheria.

This research investigates the long-forgotten relationship between diphtheria and tuberculosis. Historical medical reports from the late 19th century are reviewed followed by a statistical regression analysis of the relationship between the two diseases in the early 20th century. Historical medical reports show a consistent association between diphtheria and tuberculosis that can increase the likelihood and severity of either disease in a co-infection. The statistical analysis uses historical weekly public health data on reported cases in five American cities over a period of several years, finding a modest but statistically significant relationship between the two diseases. No current medical theory explains the association between diphtheria and tuberculosis. Alternative explanations are explored with a focus on how the diseases assimilate iron. In a co-infection, the effectiveness of tuberculosis at assimilating extracellular iron may lead to increased production of diphtheria toxin, worsening that disease, which may, in turn, exacerbate tuberculosis. Iron-dependent repressor genes connect both diseases.