The indoor temperature of dwellings in Montérégie: A better understanding for better interventions

Heat waves have significant health impacts, and the relationship between outdoor temperature and mortality is well documented. The alert and mobilization thresholds for the health network and its partners are based on outside temperatures and aim to avoid excess mortality. However, the indoor temperature of housing would provide a better indication of heat exposure for individuals who spend the majority of their time there. From a prevention perspective, it would be appropriate to focus on behavioural adaptation measures as well as the measures that have been implemented in the dwelling and the warning signs of heat-related problems, in the aim of avoiding complications and the recourse to emergency medical services. Little research exists on the relationship between indoor temperature, public health consequences and the effect of such measures.

Document the relationship between measured indoor temperature and various health outcomes in a heat-vulnerable population, while accounting for the influence of adaptive behaviors adopted by individuals; housing-related adaptations; and social and material disadvantage.

• Recruitment of 300 participants aged 60 and over, residing within the territories of the CISSS de la Montérégie-Centre and the CISSS de la Montérégie-Est Integrated Health and Social Services Centres

• Data collection over the course of two summers (2017 and 2018) with three measurement times each summer: cool weather (18 to 22°C), hot weather (28 to 30°C) and very hot weather (30 to 33°C)

• Use of temperature recording thermometers for the collection of meteorological data in the home (temperature and humidity)

• Use of questionnaires to collect data on the home (variables on the built environment) and on the participant (the usual sociodemographic variables, health effects, personal coping behaviours and adaptation measures of the dwelling)

• Exploration of the link between indoor temperatures and health outcomes, while taking into account adaptive behaviours and material and social disadvantages

An area in the agglomeration of Longueuil was initially chosen for the study since individuals’ vulnerability to heat there is similar to that of all Quebecers in terms of the proportion of seniors and people living alone or below the low-income cutoff. In terms of residential building types, the data shows that the agglomeration of Longueuil and the rest of Quebec are similar. The area under study was circumscribed for reasons of feasibility (travel time for the installation of recording thermometers). An urban area was chosen because these environments are more prone to heat problems. However, recruitment difficulties were encountered, which led the project team to expand the area to the entire territories of the CISSSs in Montérégie-Centre and Montérégie-Est, whether urban or rural. A total of 277 participants were reached at each of the three measurement times for the assessment of heat-related symptoms. The average age of the participants was 73 years. The majority of the group were women (80%), people whose highest level of education was a high school diploma (59%), people living alone (81%) and people with at least one chronic disease (65%).

The analyses show that the built environment has an influence on temperatures inside the home. For example, dwellings located in buildings with 24 or more dwellings, those located under the roof and those located in a heat island were warmer. Given their vulnerability to heat, it is preferable for seniors to live in buildings with fewer units, on lower levels and away from heat islands. These elements should be taken into account in housing construction projects, particularly in the context of densification, which has been promoted in recent years and favours very high buildings.

For many of the symptoms studied, the likelihood of experiencing them increases with indoor temperatures. In very hot weather, 30°C and above, the following symptoms were reported more often compared to in cooler weather:

• Cramps (26%)

• Dry mouth (27%)

• Feeling more thirsty than usual (53%)

•  Urinating less frequent than usual (13%)

• Darker urine than usual (14%)

• Feeling more tired than usual (46%)

• Nausea (11%)

• Trouble sleeping (31%)

The risk of experiencing many of these symptoms can increase rapidly with home temperature. These results are presented in Figure 1.

According to the analyses performed, preventive behaviours (e.g. drinking water) and adaptation of the dwelling (e.g. a fan) did not modulate the impact of temperature on the reported symptoms. Note that many coping behaviours were adopted by few people, which may limit the conclusions. It is also possible that the people who adopted the behaviours did so when the symptoms were already felt.

In Quebec, the mobilization thresholds of the healthcare system and its partners are based on outside temperatures. These thresholds have several limitations. In addition, the data from a weather station applies to the entire area concerned by these thresholds, even if this data is not necessarily representative of the entire area. The temperature thresholds were established to prevent excess mortality. They are not intended to prevent morbidity, such as increased emergency room visits or hospitalizations.
 

Figure 1. likelihood of reporting heat-related symptoms by temperature. From left to right: dry mouth, thirst, sleep disturbance, less frequent urination.

The dose-response relationship identified for dry mouth, thirst, fatigue, less frequent urine, darker urine and sleep disturbances could be used to improve interventions during a heat wave. The following recommendations are proposed to improve the response to heat waves:

• Disseminate the results of this study to CISSS staff (client program managers, emergency measures managers, home care nurses, etc.)

• Disseminate the results of this study to the managers of seniors’ housing

• Using the data collected in this study, explore the possibility of determining an indoor temperature threshold from symptom curves as a function of maximum temperature and use this threshold to equip home care workers

Université McGill