The evidence of involvement of microorganisms in the major chronic diseases and in the underlying biophysiological disorders suggests that the infectious disease environment is still a considerable influence on health and mortality risk. The classification of only 3% of deaths in England and Wales as due to infections, including urinary tract infections, is therefore somewhat misleading. External causes (accidents, suicide, and violence) account for 4% of deaths, while other categories include many common chronic diseases that have suspected or confirmed links with infection. About 6% of deaths in 2010 were due to cancers with confirmed infectious etiology, and microbial involvement is suspected in many other forms of cancer that caused a further 22% of deaths. Most of the respiratory diseases that caused 14% of deaths involve infections at some stage, and most forms of cardiovascular disease that caused 32% of deaths have some association with microorganisms, and a causal role is strongly suspected in some disorders. In total, these three major categories of disease—cardiovascular disease, cancer, and respiratory disease—accounted for about 74% of deaths (appendix E). For some of the 15% of deaths attributed to digestive, endocrine, musculoskeletal, nervous, genitourinary, and other diseases, and mental disorders (4%), there is also evidence indicating possible microbial involvement. Some of the associations are referred to at the end of this chapter, while the main focus here is on four of the subcategories of common chronic disease that account for 4% of deaths, as there is strong evidence of microbial involvement or confirmed infectious etiology.

Specific microorganisms and infections are suspected of having some role in the processes underlying cirrhosis of the liver, diabetes mellitus, and nephritis/ nephrosis. Peptic ulcer will be considered first as the causal role of a specific microorganism, Helicobacter pylori, has already been established. As indicated in chapter 2, criteria for establishing causality are often difficult to apply when a specific pathogen is found to be associated with chronic disease morbidity or mortality. This applies to the other diseases briefly reviewed in the last section of this chapter. The general theme being developed here is that the infectious disease environment continues to be of major significance for morbidity and mortality, despite the decline in mortality attributed directly to acute infectious diseases and tuberculosis and the overwhelming predominance of other chronic diseases.