Socioeconomic level and associations between heat exposure and all-cause and cause-specific hospitalization in 1,814 Brazilian cities: A nationwide case-crossover study

Background Heat exposure, which will increase with global warming, has been linked to increased risk of a range of types of cause-specific hospitalizations. However, little is known about socioeconomic disparities in vulnerability to heat. We aimed to evaluate whether there were socioeconomic disparities in vulnerability to heat-related all-cause and cause-specific hospitalization among Brazilian cities. Methods and findings We collected daily hospitalization and weather data in the hot season (city-specific 4 adjacent hottest months each year) during 2000–2015 from 1,814 Brazilian cities covering 78.4% of the Brazilian population. A time-stratified case-crossover design modeled by quasi-Poisson regression and a distributed lag model was used to estimate city-specific heat–hospitalization association. Then meta-analysis was used to synthesize city-specific estimates according to different socioeconomic quartiles or levels. We included 49 million hospitalizations (58.5% female; median [interquartile range] age: 33.3 [19.8–55.7] years). For cities of lower middle income (LMI), upper middle income (UMI), and high income (HI) according to the World Bank’s classification, every 5°C increase in daily mean temperature during the hot season was associated with a 5.1% (95% CI 4.4%–5.7%, P < 0.001), 3.7% (3.3%–4.0%, P < 0.001), and 2.6% (1.7%–3.4%, P < 0.001) increase in all-cause hospitalization, respectively. The inter-city socioeconomic disparities in the association were strongest for children and adolescents (0–19 years) (increased all-cause hospitalization risk with every 5°C increase [95% CI]: 9.9% [8.7%–11.1%], P < 0.001, in LMI cities versus 5.2% [4.1%–6.3%], P < 0.001, in HI cities). The disparities were particularly evident for hospitalization due to certain diseases, including ischemic heart disease (increase in cause-specific hospitalization risk with every 5°C increase [95% CI]: 5.6% [−0.2% to 11.8%], P = 0.060, in LMI cities versus 0.5% [−2.1% to 3.1%], P = 0.717, in HI cities), asthma (3.7% [0.3%–7.1%], P = 0.031, versus −6.4% [−12.1% to −0.3%], P = 0.041), pneumonia (8.0% [5.6%–10.4%], P < 0.001, versus 3.8% [1.1%–6.5%], P = 0.005), renal diseases (9.6% [6.2%–13.1%], P < 0.001, versus 4.9% [1.8%–8.0%], P = 0.002), mental health conditions (17.2% [8.4%–26.8%], P < 0.001, versus 5.5% [−1.4% to 13.0%], P = 0.121), and neoplasms (3.1% [0.7%–5.5%], P = 0.011, versus −0.1% [−2.1% to 2.0%], P = 0.939). The disparities were similar when stratifying the cities by other socioeconomic indicators (urbanization rate, literacy rate, and household income). The main limitations were lack of data on personal exposure to temperature, and that our city-level analysis did not assess intra-city or individual-level socioeconomic disparities and could not exclude confounding effects of some unmeasured variables. Conclusions Less developed cities displayed stronger associations between heat exposure and all-cause hospitalizations and certain types of cause-specific hospitalizations in Brazil. This may exacerbate the existing geographical health and socioeconomic inequalities under a changing climate.
In this nationwide cohort study, Rongbin Xu and colleagues investigate heat and hospitalisations in cities of different socioeconomic development.
Author summary Why was this study done? Heat exposure is associated with increases in mortality and morbidity, but vulnerability to heat is not evenly distributed. It remains uncertain whether the magnitude of heat impacts on all-cause and cause-specific hospitalizations is associated with local socioeconomic characteristics. What did the researchers do and find? We performed case-crossover analyses based on a nationwide dataset with 49 million hospitalizations in the hot season during 2000–2015 in 1,814 Brazilian cities. We found that less developed cities showed higher increased all-cause and cause-specific hospitalization than more developed cities when exposed to the same temperature rise during the hot season. These inter-city socioeconomic disparities in associations of heat with health outcomes were particularly notable for hospitalizations of children and adolescents, and for hospitalizations due to ischemic heart disease, asthma, pneumonia, renal diseases, mental health conditions, and neoplasms. What do these findings mean? Increasing heat exposure along with global warming could be a potential driver for exacerbating inter-city health inequalities. More attention should be paid to less developed cities in Brazil to tackle the morbidity burden of heat exposure, in order to promote health equity under global warming.