Chronic disease increases the odds of hospitalization from heat exposure, study finds

By Priyanjana Pramanik, MSc.May 8 2024Reviewed by Lily Ramsey, LLM

In a recent study published in eBioMedicine, researchers investigated the impact of ambient heat exposure on hospitalizations among individuals with varying numbers and combinations of chronic diseases.

Their results indicate that as the number of chronic diseases increased, particularly among older individuals, males, and non-indigenous people, the odds of hospitalization associated with heat exposure also increased, highlighting the importance of addressing multimorbidity as a distinct and vulnerable subgroup in heat-health action plans.

Study: Multimorbidity and emergency hospitalisations during hot weather. Image Credit: Dragan Mujan/Shutterstock.com

Background

Exposure to hot weather risks human health, prompting the development of heat-health action plans (HHAPs) to mitigate these risks through early warnings and intervention strategies.

While individuals with specific chronic diseases like cardiovascular issues are recognized as vulnerable to heat, the impact of multimorbidity (having multiple chronic conditions) on heat-related health risks remains unclear.

Despite the prevalence of multimorbidity, there's limited evidence on its association with heat-health risks, hindering nuanced targeting in HHAPs.

Additionally, hospitals and health services need to be alerted about potential increases in patient volume during heat waves for adequate preparedness.

About the study

This study aimed to address these gaps by investigating the association between heat exposure and hospitalizations among individuals with varying numbers and combinations of chronic diseases, shedding light on the specific conditions most affected and highlighting the importance of considering multimorbidity in heat-health planning.

This study used data from the hospital registry in Queensland, Australia, to analyze emergency hospitalizations from March 2004 to April 2016 in eight cities/communities.

Information collected included demographics, clinical data, and daily ambient temperature at the postcode level.

The study included individuals aged 15 and above and categorized them into working-age and older groups as well as indigenous and non-indigenous categories. Socioeconomic status was determined using area-level indexes.

Chronic diseases were identified using the International Classification of Diseases codes, focusing on five groups: cardiovascular disease, diabetes, mental disorders, asthma or Chronic Obstructive Pulmonary Disease (COPD), and chronic kidney disease.

The association between ambient heat exposure and hospitalizations was assessed using a time-stratified case-crossover design, analyzing odds ratio (ORs) with a five-degree celsius increase in mean temperature. Subgroup analyses were conducted based on age, sex, indigenous status, and socioeconomic status.

Additionally, sensitivity analyses were performed to test the results' robustness, including including Parkinson's disease as a chronic disease group and adjusting for potential harvesting effects of heat exposure.

Findings

The study analyzed 2,263,427 hospitalizations from Queensland's eight cities/communities, covering individuals with varying chronic diseases.

Older individuals (≥65 years) showed higher proportions of multiple chronic diseases compared to working-age individuals, with males and indigenous people also exhibiting slightly higher proportions of various chronic diseases.

The odds of an individual being hospitalized for any cause increased with the number of chronic diseases they had. This was particularly true for non-indigenous people, males, and older individuals.

Specifically, older individuals with multiple chronic diseases had significantly higher ORs of hospitalizations associated with a 5°C mean temperature increase compared to those with no chronic diseases, ranging from 1.00 to 1.13.

Among chronic diseases, asthma/COPD and chronic kidney disease, either alone or when combined with other diseases, were linked to the largest ORs of hospitalizations.

Cardiovascular disease combined with other chronic diseases had the highest number of hospitalizations, which could be attributed to heat.

In individuals with multimorbidity, i.e., having two or more chronic diseases, the ORs of hospitalizations for various conditions, including infectious and parasitic disease, urological disease, and heat-related illness, significantly increased with a 5°C rise in mean temperature, indicating heightened vulnerability.

Sensitivity analyses confirmed the robustness of the main findings across different conditions and temperature metrics, ensuring the reliability of the study's conclusions.

Conclusions

The study highlights several important findings regarding the association between chronic diseases and hospitalizations during hot weather.

Firstly, the probability of being hospitalized increased with the number of chronic diseases, especially in older individuals, males, and non-indigenous people.

Asthma/COPD and chronic kidney disease, either alone or when experienced with other diseases, were linked with the greatest probability of being hospitalized.

Secondly, individuals with multimorbidity experienced significantly increased odds of cause-specific hospitalizations during hot weather, particularly urological disease, heat-related illness, and infectious or parasitic disease.

The study suggests implications for heat-health action plans to prioritize subgroups most at risk, such as those with multimorbidity, for targeted interventions during heat waves.

The study's strengths include the comprehensive analysis of chronic disease types and combinations, the use of statewide data to provide a representative sample, and the advanced analytical approach employed.

However, limitations include the restriction to five groups of chronic diseases, potential exposure measurement bias, inability to adjust for humidity, and the study's observational nature, which precludes establishing causality.

Further research is needed to explore the influence of the duration and severity of chronic diseases on heat health risk and to develop effective strategies for reducing heat-related health risks in individuals with multimorbidity.