METHODS: We conducted a two-stage time-stratified case-crossover study to examine the association between temperature and under-five mortality, spanning the period from 2014 to 2018 across all six regions in Malaysia. In the first stage, we estimated region-specific temperature-mortality associations using a conditional Poisson regression and distributed lag nonlinear models. We used a multivariate meta-regression model to pool the region-specific estimates and examine the potential role of local characteristics in the association, which includes geographical information, demographics, socioeconomic status, long-term temperature metrics, and healthcare access by region.
RESULTS: Temperature in Malaysia ranged from 22 °C to 31 °C, with a mean of 27.6 °C. No clear seasonality was observed in under-five mortality. We found no strong evidence of the association between temperature and under-five mortality, with an "M-" shaped exposure-response curve. The minimum mortality temperature (MMT) was identified at 27.1 °C. Among several local characteristics, only education level and hospital bed rates reduced the residual heterogeneity in the association. However, effect modification by these variables were not significant.
CONCLUSION: This study suggests a null association between temperature and under-five mortality in Malaysia, which has a tropical climate. The "M-" shaped pattern suggests that under-fives may be vulnerable to temperature changes, even with a small temperature change in reference to the MMT. However, the weak risks with a large uncertainty at extreme temperatures remained inconclusive. Potential roles of education level and hospital bed rate were statistically inconclusive.
METHODS: In this longitudinal study, we randomly selected community members aged between 18 and 70 years who resided in Segamat district of Johor state, Malaysia. Over 21 days, we conducted three home visits to each participant. During each visit, participants completed a questionnaire consisting of Likert scale, multiple choice, and free text questions and we collected quantitative and qualitative data. These inquiries assessed the participants' perception of heat as health threat, whether or not they took heat preventive measures, and the specific protective measures they routinely employed. Descriptive data analyses were conducted and patterns of protective measures were investigated.
FINDINGS: Between March 29 and July 31, 2023, 120 participants (72 women and 48 men) completed 360 questionnaires over three home visits. Initially, 58% participants recognised heat hazards to daily activities, decreasing to 42% and 35% by visits 2 and 3. Participants took preventive measures throughout the day, which was consistently high between 1200 h and 1400 h, with 77% of participants taking preventive measures on visit 1, 82% on visit 2, and 82% on visit 3. Use of preventive measures was also high between 1400 h and 1730 h, with 77% using preventive measure on visit 1, 81% on visit 2, and 79% on visit 3. The most common protective measures were fans (used by 68-88% of participants), drinking more water (70-78% of participants), and resting (44-72% of participants). The least common were relocating to cooler places, removing clothes, and using wet towels (0-2·5%). Despite high temperatures, perceptions of heat risks decreased over time. Participants took basic protections, especially at midday, but improved literacy and affordable cooling options are needed to protect vulnerable rural populations.
INTERPRETATION: Our findings underline the need to improve heat literacy and adaptation as only half of the population assessed perceived heat as a potential health hazard and practised limited heat protective measures. Addressing climate change and health necessitates fundamental behavioural changes on the part of individuals and communities, to protect them against the adverse effects of heat.
FUNDING: Monash University Malaysia and Heidelberg Institute of Global Health, Heidelberg University.