Heat Stress Impacts on Cardiac Mortality in Nepali Migrant Workers in Qatar

Qatar is a major destination country for Nepali migrant workers (NMWs; main age range 25-35 years) in the construction trade. These 120,000+ NMWs are exposed to various occupational hazards, including excessive heat, and 3-4 workers die each week. Our study aimed to show whether heat exposure caused deaths.

The worker population and mortality data of NMWs were retrieved from government institutions in Nepal. Heat exposure was assessed by monthly estimates of daily wet bulb globe temperature (WBGT), for in-shade conditions, from data collected at the Doha weather station from 2009 to 2017. Working in the sun during the middle of the day would add 2-3°C to the in-shade WBGT values. Daily deaths and their causes were obtained from the records of the Foreign Employment Promotion Board (FEPB) in Nepal, 2009-2017. Interviews with returning NMWs about their working conditions and the impacts of these conditions added information. The association between the heat variable and mortality was tested with standard statistical methods.

The average annual death rate for NMWs in Qatar was 150 deaths/100,000. According to interviews, the majority of NMWs were found working in high WBGT (>31°C) each working day during hot months. The major cause of these deaths was recorded as cardiovascular problems (cardiovascular disease; CVD). Unfortunately, the causes of death were poorly described, and many deaths were listed as "cardiac arrest." We included these deaths in the broader category of "cardiovascular causes." There was a strong correlation between average monthly afternoon heat levels (WBGT) and CVD mortality. It is likely that a large proportion of these CVD deaths during hot months were due to serious heat stroke. Global studies show that approximately 15% of deaths in the age group 25-35 years are due to CVD causes. However, in this NMW population, the figures were 22% during the cool season and 58% during the hot season.

The increased CVD mortality during hot periods is most likely due to severe heat stress. As many as 200 of the 571 CVD deaths during 2009-2017 could have been prevented if effective heat protection had been implemented as a part of local occupational health and safety programs. There is an urgent need for protection against such heat effects among NMWs, and rising temperatures from ongoing climate change are further increasing the health risks. Cause of death records for workers dying in hot conditions should be more precise than "cardiac arrest."