Individual factors underlie temperature variation in sickness and in health: influence of age, BMI and genetic factors in a multi-cohort study

Abstract

AbstractIntroductionAgeing affects immune function resulting in aberrant fever response to infection. We assess the effects of biological variables on basal temperature and temperature in COVID-19 infection, proposing an updated temperature threshold for older adults.MethodsParticipants:Unaffected twin volunteers: 1089 adult TwinsUK participants.London hospitalised COVID-19+: 520 adults with emergency admission.Birmingham hospitalised COVID-19+: 757 adults with emergency admission.Community-based COVID-19+: 3972 adults self-reporting a positive test using the COVID Symptom Study mobile application.AnalysisHeritability assessed using saturated and univariate ACE models; Linear mixed-effect and multivariable linear regression analysing associations between temperature, age, sex and BMI; multivariable logistic regression analysing associations between fever (≥37.8°C) and age; receiver operating characteristic (ROC) analysis to identify temperature threshold for adults ≥ 65 years.ResultsAmong unaffected volunteers, lower BMI (p=0.001), and older age (p<0.001) associated with lower basal temperature. Basal temperature showed a heritability of 47% (95% Confidence Interval 18-57%).In COVID-19+ participants, increasing age associated with lower temperatures in cohorts (c) and (d) (p<0.001). For each additional year of age, participants were 1% less likely to demonstrate a fever (OR 0.99; p<0.001).Combining healthy and COVID-19+ participants, a temperature of 37.4°C in adults ≥65 years had similar sensitivity and specificity to 37.8°C in adults <65 years for discriminating fever in COVID-19.ConclusionsAgeing affects temperature in health and acute infection. Significant heritability indicates biological factors contribute to temperature regulation.Our observations indicate a lower threshold (37.4°C) should be considered for assessing fever in older adults.Key PointsOlder adults, particularly those with lower BMI, have a lower basal temperature and a lower temperature in response to infectionBasal temperature is heritable, suggesting biological factors underlying temperature regulationOur findings support a lower temperature threshold of 37.4°C for identifying possible COVID-19 infection in older adultsThis has implications for case detection, surveillance and isolation and could be incorporated into observation assessment