Incorporating social environment data in infectious disease research

This article proposes several conceptual perspectives designed to advance our understanding of the material and experiential conditions contributing to persistent disparities in rates of morbidity and mortality among groups unequal in their social and economic statuses. An underlying assumption is that these disparities, which are in clear evidence at mid- and late life, may be anchored to earlier circumstances of the life course. Of particular interest are those circumstances resulting in people with the least privileged statuses having the greatest chances of exposure to health-related stressors. Among the stressors closely linked to status and status attainment are those that continue or are repeated across the life course, such as enduring economic strain and discriminatory experiences. Also taking a long-range toll on health are circumstances of stress proliferation, a process that places people exposed to a serious adversity at risk for later exposure to additional adversities. We suggest that this process can be observed in instances of trauma, in early out-of-sequence transitions, and in the case of undesired changes that disrupt behaviors and relationships in established roles. Effective effort to close the systemic health gaps must recognize their structural underpinnings.

It is not known whether psychological stress suppresses host resistance to infection. To investigate this issue, we prospectively studied the relation between psychological stress and the frequency of documented clinical colds among subjects intentionally exposed to respiratory viruses. After completing questionnaires assessing degrees of psychological stress, 394 healthy subjects were given nasal drops containing one of five respiratory viruses (rhinovirus type 2, 9, or 14, respiratory syncytial virus, or coronavirus type 229E), and an additional 26 were given saline nasal drops. The subjects were then quarantined and monitored for the development of evidence of infection and symptoms. Clinical colds were defined as clinical symptoms in the presence of an infection verified by the isolation of virus or by an increase in the virus-specific antibody titer. The rates of both respiratory infection (P less than 0.005) and clinical colds (P less than 0.02) increased in a dose-response manner with increases in the degree of psychological stress. Infection rates ranged from approximately 74 percent to approximately 90 percent, according to levels of psychological stress, and the incidence of clinical colds ranged from approximately 27 percent to 47 percent. These effects were not altered when we controlled for age, sex, education, allergic status, weight, the season, the number of subjects housed together, the infectious status of subjects sharing the same housing, and virus-specific antibody status at base line (before challenge). Moreover, the associations observed were similar for all five challenge viruses. Several potential stress-illness mediators, including smoking, alcohol consumption, exercise, diet, quality of sleep, white-cell counts, and total immunoglobulin levels, did not explain the association between stress and illness. Similarly, controls for personality variables (self-esteem, personal control, and introversion-extraversion) failed to alter our findings. Psychological stress was associated in a dose-response manner with an increased risk of acute infectious respiratory illness, and this risk was attributable to increased rates of infection rather than to an increased frequency of symptoms after infection.

Summary Background Although loneliness and social isolation have been linked to an increased risk of non-communicable diseases such as cardiovascular disease and dementia, their association with the risk of severe infection is uncertain. We aimed to examine the associations between loneliness and social isolation and the risk of hospital-treated infections using data from two independent cohort studies. Methods We assessed the association between loneliness and social isolation and incident hospital-treated infections using data for participants from the UK Biobank study aged 38–73 years at baseline and participants from the nationwide population-based Finnish Health and Social Support (HeSSup) study aged 20–54 years at baseline. For inclusion in the study, participants had to be linked to national health registries, have no history of hospital-treated infections at or before baseline, and have complete data on loneliness or social isolation. Participants with missing data on hospital-treated infections, loneliness, and social isolation were excluded from both cohorts. The outcome was defined as a hospital admission with a primary diagnosis of infection, ascertained via linkage to electronic health records. Findings After exclusion of 8·6 million participants for not responding or not providing appropriate consent, the UK Biobank cohort consisted of 456 905 participants (249 586 women and 207 319 men). 26 860 (6·2%) of 436 001 participants with available data were reported as being lonely and 40 428 (9·0%) of 448 114 participants with available data were socially isolated. During a median 8·9 years (IQR 8·0–9·6) of follow-up, 51 361 participants were admitted to hospital due to an infectious disease. After adjustment for age, sex, demographic and lifestyle factors, and morbidities, loneliness was associated with an increased risk of a hospital-treated infection (hazard ratio [HR] 1·12 [95% CI 1·07–1·16]), whereas social isolation was not (HR 1·01 [95% CI 0·97–1·04]). Of 64 797 individuals in the HeSSup cohort, 18 468 (11 367 women and 7101 men) were eligible for inclusion. 4466 (24·4%) of 18 296 were lonely and 1776 (9·7%) of 18 376 socially isolated. During a median follow-up of 10·0 years (IQR 10·0–10·1), 814 (4·4%) participants were admitted to hospital for an infectious disease. The HRs for the HeSSup study replicated those in the UK Biobank (multivariable-adjusted HR for loneliness 1·32 [95% CI 1·06–1·64]; 1·08 [0·87–1·35] for social isolation). Interpretation Loneliness might increase susceptibility to severe infections, although the magnitude of this effect appears modest and residual confounding cannot be excluded. Interventional studies are required before policy recommendations can advance. Funding Academy of Finland, the UK Medical Research Council, and Wellcome Trust UK.