Although biomedical research has guided the discovery of cures and treatments for many infectious illnesses, the emergence/reemergence of infectious diseases continues today. Newly emerging infectious diseases as well as those that persist often affect populations that are deprived of social resources. The role of social inequalities has been noted in the emergence of infections such as HIV/AIDS, malaria, and other infections. Despite calls for a social determinants approach to the study and prevention of infectious diseases at the population level, much of the infectious disease literature continues to focus on proximate elements associated with infections rather than distal determinants of existing and new pathogenic threats to health. This proximate focus is beginning to shift and there is growing body of research examining social determinants of a wide array of infectious disease topics.
EPID880
The Epidemiological Links between Infection and Chronic Disease
Fall
term(s)
3 Credit Hour(s)
Instructor(s):
Aiello, Allison
Last offered Fall 2007
Prerequisites: EPID 658 and EPID 605, 607, 609
Exploring the Link between Infection and Chronic Disease: Research Challenges and Pathways
As early as the mid 19th century researchers were exploring the idea that chronic conditions, such as cancer, were caused by infectious organisms. During the epidemiological transition when the book on infectious diseases was thought to be closed and the concomitant increase in research on "life-style" factors began to flourish, a line was formed distinguishing chronic and infectious disease research agendas. This distinction has been dissolving as an increasing number of infections are being implicated in the mutlifactorial risk profiles of chronic health outcomes. Examples include the link between Helicobater pylori infection and peptic ulcer disease, human papilloma virus and cervical cancer cases, and the growing body of research examining the link between infection and cardiovascular disease.
The use of observational studies for assessing the relationship between infection and chronic health outcomes have been called into question since randomized clinical trials examining the effect of anti-infective treatments on incidence of chronic disease have shown equivocal results. The dynamic nature of the pathways by which infection may influence chronic disease has implications on the use of the randomized clinical trial as the "gold-standard" for assessing these links. It is evident that there are numerous methodological, sociological, and biological factors that must be considered when evaluating the epidemiological literature supporting a link between infection and chronic disease. Some examples of these issues include the need to:
" Explore the role of co-factors and the influence of socioeconomic and other demographic determinants on the pathways between infection and chronic disease outcomes
" Assess the type of damage that may be caused by a particular organism. For example, some organisms may act in a hit-and-run manner that triggers chronic disease processes well after the widow of detection of the invading organism has passed
" Measure and characterize latent and recurrent infections as well as immune response, since latent and recurrent infections may cause repeated damage over the lifecourse
" Gather data on the interaction between co-infections or overall burden of infection with multiple pathogens
" Detect new infectious organisms and devise methods for isolating organisms from tissue or serum
Examples abound that demonstrate the complicated epidemiology concerning the link between infection and chronic conditions. Understanding the influences of demographic shifts, timing of infection and social processes can help elucidate these linkages. The association between H. pylori infection and stomach cancer illustrate these issues well:
" Demographic shifts: There are strong disparities in the prevalence of stomach cancer between the US and lesser developed countries. In the US, the incidence in stomach cancer has dropped steadily since the 1900's but the incidence in lesser developed countries is still high.
" Timing of infection: The disparity in cancer prevalence could be explained by age at infection, since H.pylori infection is likely to occur at younger ages among individuals living in lesser developed areas compared to the US. Therefore, individuals in lesser developed countries may be infected with H. pylori for a longer period of time, leading to higher levels of damage to the stomach.
" Social processes: Studies have reported a stronger association between low socioeconomic position in childhood compared to adult socioeconomic position and incidence of stomach cancer in adulthood. It appears that socioeconomic determinants in childhood shape adult risk of stomach cancer, independent of adult socioeconomic status. Therefore, lifecourse socioeconomic processes influence the link between H. pylori infection and later life chronic disease outcomes.
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