Association of daily temperature at residence with mortality in Eastern Massachusetts

Studies reported increased mortality during heat waves worldwide. While these studies used daily central site temperature as the exposure variable, temperature is spatially variable, and housing and landscape characteristics affect exposure. To investigate acute and chronic effects of temperature on mortality we developed a spatio-temporal model for temperature in Eastern Massachusetts for 2000 to 2004 and applied it to a case-crossover study. We obtained daily temperature measurements from four different data sources. Land use, elevation and census data were obtained. The prediction model for daily temperature at an address included daily intercepts and smooth functions of space, season-specific smooth functions of space, distance to coastline, elevation and land use. Mortality data were obtained from Massachusetts Department of Public Health. Residences of the 125,409 out-of-hospital-deaths were geocoded. A case-crossover analysis was conducted with estimated temperatures at place of residence as exposure variable. Piecewise linear splines of maximum temperature with knots at 4 and 27°C allowed for non-linearity. We compared our results using temperature at Logan Airport as the exposure variable. Each 1°C increase at temperatures between 4 and 27°C was associated with an increased mortality risk of 0.3% (95% CI 0.1–0.4%) for temperature at residence as well as at Boston Logan Airport. An increase in daily maximum temperature at place of residence when above 27°C increased the risk of mortality by 1.6% (95% CI 1.0–2.1%) per 1°C. Compared to this the association of mortality with maximum temperature at Logan Airport was somewhat smaller. These effects were higher for subjects living at residences with high location-specific average temperature level. The results suggest that the observed associations between hot temperatures and mortality may be underestimated when using central site monitoring data. Furthermore living in an area with hot average temperature may increase the risk of mortality associated with hot temperatures.