Research Article: Temporal changes in the effects of ambient temperatures on hospital admissions in Spain

Date Published: June 13, 2019

Publisher: Public Library of Science

Author(s): Èrica Martínez-Solanas, Xavier Basagaña, Jeffrey Shaman.


The exposure to extreme ambient temperatures has been reported to increase mortality, although less is known about its impact on morbidity. The analysis of temporal changes in temperature-health associations has also focused on mortality with no studies on hospitalizations worldwide. Studies on temporal variations can provide insights on changes in susceptibility or on effectiveness of public health interventions. We aimed to analyse the effects of temperature on cause-specific hospital admissions in Spain and assess temporal changes using two periods, the second one characterized by the introduction of a heat health prevention plan.

Daily counts of non-scheduled hospital admissions for cardiovascular, cerebrovascular and respiratory diseases and daily maximum temperature were obtained for each Spanish province for the period 1997–2013. The relationship between temperature and hospitalizations was estimated using distributed lag non-linear models. We compared the risk of hospitalization due to temperatures (cold, heat and extreme heat) in two periods (1997–2002 and 2004–2013).

Cold temperatures were associated with increased risk of cardiovascular, cerebrovascular and respiratory hospital admissions. Hot temperatures were only associated with higher hospital admissions for respiratory causes while hospitalizations for cardiovascular and cerebrovascular diseases did not increase with heat. There was a small reduction in heat-related respiratory admissions in period 2. Whereas cold-related hospitalizations for cardiovascular and cerebrovascular diseases increased in period 2, a significant reduction for respiratory hospitalizations was reported.

Our results suggested that heat had an adverse impact on hospital admissions for respiratory diseases, while cold increased the risk of the three studied cause-specific hospitalizations. Public health interventions should also focus on morbidity effects of temperature.

Partial Text

Exposure to extreme ambient temperatures is an important public health hazard. The most reported health impacts of extreme temperatures have been increases in mortality, especially among the most vulnerable individuals such as the elderly and those with prior medical conditions [1,2]. A large study conducted in 13 countries estimated that around 8% of deaths can be attributable to temperatures [3]. In Spain this number was 6.5% and the highest mortality was associated with cold temperatures.

Overall, 37,278,921 hospital admissions were registered in Spain during the study period. Restricting to the three selected causes, the number of hospitalizations was 10,550,849. Cardiovascular and respiratory diseases were the major causes of hospitalization (around 12% and 13%, respectively), while admissions for cerebrovascular diseases accounted for 3.5% of hospitalizations (Table 1). Cardiovascular and cerebrovascular hospitalizations were sex-balanced, while men suffered more hospitalizations due to respiratory diseases (Table 1). In terms of age, the three causes analysed had a similar distribution. Barcelona and Madrid were the provinces that registered the highest percentage of hospitalizations (S2 Table). An important climatic variability was observed among the Spanish provinces, with a daily mean temperature ranging from 16.9° in Leon to 25.7° in Sevilla (S2 Table). The distribution of all-cause hospital admissions and daily maximum temperature by month and day of the week is reported in Supporting Information (S3 Table).

We performed a country-wide study on the relationship between ambient temperature and hospital admissions in Spain. Our results showed an increase in the risk of hospital admissions for respiratory causes with heat. Heat did not increase the risk of hospitalizations by cardiovascular or cerebrovascular diseases. Cold temperatures increased the risk of cardiovascular, cerebrovascular and respiratory diseases. The study period (1997–2013) was divided in two, the second one characterized by the introduction of a HHPP. There was a slight reduction of heat-related hospitalizations for respiratory diseases in period 2, and slight increases in cold-related hospitalizations for cardiovascular and cerebrovascular diseases in period 2 compared to period 1. However cold-related hospitalizations for respiratory diseases showed an important drop in period 2 compared to period 1.