Socioeconomic and Race/Ethnic Patterns in Persistent Infection Burden Among U.S. Adults

HEALTH of U.S. adults is strongly associated with their socioeconomic position (1). Adults with more education and income have a lower burden of disease, fewer physical limitations, less disability, and longer life expectancy (2–4). The pathophysiological mechanisms linking lower socioeconomic position (SEP) to worse health, however, are poorly understood. Exposure to infections and inflammation has been proposed as a potentially important determinant of chronic disease and mortality risk (5), but current knowledge of the socioeconomic patterning of infection burden in the U.S. population is limited. Increasing evidence points to links between chronic disease and persistent infections including herpesviruses, Helicobacter pylori, periodontal pathogens, and hepatitis viruses. For example, the herpesviruses cytomegalovirus (CMV) and herpes simplex virus type 1 (HSV-1) have been linked to cardiovascular disease, frailty, cognitive outcomes, and Alzheimer's disease (6–9). Infection with CMV and HSV-1 is common in childhood (10), with the viruses remaining latent in the host throughout the life course. The bacterium H. pylori can also lie dormant in the body for decades until the bacteria-host equilibrium is disturbed. Besides its role in peptic ulcer disease, H. pylori has been implicated in the development of stroke and ischemic heart disease through inflammatory pathways, lipid alterations, and homocysteine-induced endothelial dysfunction (11). Hepatitis B virus (HBV), known for its role in chronic liver disease, has been hypothesized to contribute to atherogenic diseases via systemic effects on immune response and colonization of vascular tissues (12,13). Common periodontal pathogens such as Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis have also been implicated in coronary heart disease and stroke and have been found in atherosclerotic plaques (14,15). Persistent infection has also been implicated as a factor in the development of functional limitations (1,5). For example, seropositivity to CMV was associated with frailty in one study, and in another study, higher CMV IgG antibody levels were associated with functional impairment (9,16). The presence of multiple persistent infections may contribute to morbidity beyond the impact of individual infections (17–20). Presence of one infection might raise the risk of other infections or increase the deleterious effects of other pathogens, or both. For example, work by Vilkuna-Rautiainen and colleagues suggests that combined infection with HSV and periodontal bacteria may increase the risk for cardiovascular disease through decreasing levels of high-density lipoprotein cholesterol more than each pathogen alone (21). From a population perspective, burden of infection and inflammation has been hypothesized as an explanation for cohort changes in life expectancy as well as black or white differences in artherosclerosis in the early 20th century (5,22,23). Recent research has begun addressing socioeconomic and race/ethnic differences in individual infection status in the United States. Adults with less education and income, as well as minorities, have been shown to have a higher prevalence of hepatitis viruses, Toxoplasma gondii, H. pylori, HSV-2, and CMV (10,24–26). Data from the Whitehall study in the UK found that employment grade was related to burden of infection as measured by the summed infection serostatus for three pathogens (CMV, HSV-1, and Chlamydia pneumonia) (27). However, there is little research on the relationship between social factors and coinfection with multiple persistent infections in the United States. Therefore, the purpose of this study was to investigate whether education, income, and race/ethnicity are related to infection burden in a representative sample of U.S. adults. In addition, we attempt to improve upon earlier approaches to studying burden of infection by constructing a novel latent variable representing multiple persistent infections within individuals.