The main focus in the next three chapters is on changes in death rates from major chronic diseases in the context of a greatly changed infectious disease environment. Although major epidemic diseases such as smallpox, typhus, typhoid, and cholera had ceased to cause high mortality and were largely eliminated from England by the end of the 19th century, many other acute infectious diseases of childhood and the chronic infectious disease tuberculosis remained prevalent. The main epidemic diseases of childhood and common respiratory and gastrointestinal infections continue to be prevalent today, although most are generally not life threatening in industrialized countries or case fatality is extremely low. Some of the acute infectious diseases convey immunity, and a specific immune response will occur whenever the microorganism is contracted throughout life. This might tend to be overlooked as the immune response prevents acute infection, although there can be biophysiological consequences that are potentially harmful, either in the short run or cumulatively. Many common viruses and bacteria are now known to be associated with particular forms of chronic disease, including the cardiovascular diseases considered in this chapter.

Bearing in mind the dramatic reduction in death rates from major epidemic diseases that had already occurred by the 1870s, cardiovascular diseases became increasingly predominant as death rates from acute infectious diseases, tuberculosis, and respiratory diseases declined (fig. 11.1). Together with the increase in the death rate from cancer, this constitutes much of the shift in cause of death that has occurred in the epidemiological transition. Cardiovascular disease and other chronic diseases are more likely to occur at older ages, and their growing predominance was linked with increased longevity resulting from the decline in infectious disease death rates. A study of the transition in Italy recognized that the distinction between communicable and noncommunicable disease is not clear-cut as infections are involved in the pathogenesis of many chronic diseases. Evidence of association between microorganisms and chronic diseases previously regarded as noncommunicable, with causality established in some cases, clearly has implications for any theory of epidemiological transition.