Landmark Tuks study on heatwave-linked mortality in SA

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South Africans 65 or older living in Cape Town, Durban and Johannesburg faced a “significant increase in mortality” from increased daily ambient apparent temperature – a combination of humidity and temperature. This is among the findings of a landmark five-year epidemiological study from the University of Pretoria (UP), which used death data from Statistics SA and information from the SA Weather Service, to investigate the association between daily ambient temperature and daily all cause non-accidental mortality in the three major cities. It’s the first study of its kind in Africa.

“Due to climate change, an increase of 3°C to 4°C in ambient temperature is projected along the South African coast and 6°C to 7°C inland during the next 80 years,” writes the paper’s author, Janine Wichmann, associate professor of environmental health at the school of health systems and public health.

“It’s this likelihood of higher temperatures under climate change in South Africa that highlights the need to elucidate how the population responds to ambient temperature.”

The results suggest that the general population has an increased risk of mortality with increasing daily ambient apparent temperature above city specific thresholds. For the study, the city specific daily ambient apparent temperature thresholds were set at 18.6 degrees for Cape Town, 24.8 degrees for Durban and 18.7 degrees for Joburg. Cape Town has a Mediterranean climate; Durban has a humid subtropical climate, which borders on a tropical wet and dry climate; while Joburg has a subtropical highland climate.

Wichmann found an overall significant increase of 0.9% in mortality per one degree increase in daily ambient apparent temperature observed for all age groups combined in the three cities.

The elderly were more at risk. “For the plus-65 year age group, a significant increase of 2.1% in mortality was observed. Physiological responses to variable ambient temperatures decline with ageing, such as reduced ability to maintain core temperature, reduced sweat gland output, reduced skin blood flow, smaller increase in cardiac output.

“The elderly are also more likely to take medication that may interfere with an already weak thermo-regulation Additionally mental disorders, such as dementia, also alter risk perception and protective behaviours. Social factors, such as living alone, living in nursing homes or being confined to bed also add to the increased risk.”

The study found the risk for all age groups combined and the elderly are similar to those reported in studies from developed and developing countries. Increased blood viscosity from dehydration, elevated cholesterol levels and a higher sweating threshold in the elderly may trigger heat-related mortality in susceptible individuals.

Few studies of this nature have been conducted in developing countries and “even fewer in Africa,” Wichmann points out. “Detailed exposure assessments need to be conducted in cities in urban and rural areas for man years. Mortality data also needs to include the neighbourhood where the person lived, so one can assume the temperature observed in the neighbourhood is what the person was exposed to mostly prior to death, unless it’s clearly stated the person died in another town, city or province.”

Abstract
Due to climate change, an increase of 3–4 °C in ambient temperature is projected along the South African coast and 6–7 °C inland during the next 80 years. The objective of this study was to investigate the association between daily ambient apparent temperature (Tapp) and daily all-cause non-accidental mortality (hereafter mortality) in Cape Town, Durban and Johannesburg during a 5-year study period (2006–2010). Susceptibility by sex and age groups (< 15 years, 15–64 years and ≥ 65 years) was also investigated. The associations were investigated with the time-stratified case-crossover epidemiological design. Models were controlled for PM10, public holidays and influenza epidemics. City-specific Tapp thresholds were determined using quasi-Poisson generalised additive models. The pooled estimates by sex and age groups were determined in meta-analyses. The city-specific Tapp thresholds were 18.6 °C, 24.8 °C and 18.7 °C, respectively for Cape Town, Durban and Johannesburg. A 3.3%, 2.6% and 2.8% increase in mortality per IQR increase in Tapp (lag0–1) was observed in Cape Town, Durban and Johannesburg, respectively above the city-specific thresholds. The elderly were more at risk in Cape Town and Johannesburg. No difference in risk was observed for males and females in the three cities. In the meta-analysis an overall significant increase of 0.9% in mortality per 1 °C increase in Tapp (lag0–1) was observed for all age groups combined in the three cities. For the ≥ 65 year group a significant increase of 2.1% in mortality was observed. In conclusion, the risks for all age groups combined and the elderly are similar to those reported in studies from developed and developing countries. The results can be used in present-day early warning systems and in risk assessments to estimate the impact of increased Tapp in the country due to climate change. Future research should investigate the association between Tapp and cause-specific mortality and also morbidity.

Authors

Wichmann, Janine

 

According to further research, around the world, numerous cases have revealed the considerable dangers of extreme heatwaves. Over 70,000 people perished to the extreme heat of the 2003 European heatwave, >10,000 people to the 2010 Russian heatwave, over 2,000 to the 2015 India heatwave, and altogether, over 800 cases of deadly heatwaves have been documented worldwide since 1980. At times, the impacts of deadly heat are not measured in human lives, but in the numbers of people imprisoned indoors.

In the last two years, for instance, millions of Americans have been told to stay indoors in cool places to avoid dangerous heat outdoors. Unfortunately, according to recent studies these deadly heatwaves are projected to worsen even with aggressive mitigation of greenhouse gases. Yet, the significance of this deadly heat will depend on the sensitivity of the human body to heat, and a new synthesis paper shows that we are more sensitive to heat than you may think.

“We know of many case examples when people have died as a result of heatwaves,” says Camilo Mora at the University of Hawaii at Manoa and lead author of the study. “However, why people died is a question whose answer is scattered.”

In this paper, the researchers carried out a systematic review of medical literature into the known ways in which heat kills people. They identified five physiological mechanisms with impacts on seven vital organs. Then, they carried out secondary searches using as keywords all possible combinations of mechanisms and vital organs to ensure a systematic search of the literature. Out of 35 possible interactions (five mechanisms times seven vital organs), the authors found medical evidence for 27 of such interactions. Basically, there are at least 27 ways in which things can go wrong during a heatwave.

Briefly, when the body is exposed to extreme heat, the hypothalamus generates a reaction in which it redirects blood flow to the skin, with the purpose of cooling down. This compensatory shunting of blood to the skin results in inadequate blood flow to other organs (a mechanism called ischaemia), where it creates anoxic conditions and damaging chemical compounds. In turn, if body temperature surpasses the optimal body temperature (because it is too hot), this will damage cells directly in a mechanism referred as heat cytotoxity. Both ischemia and heat cytotoxity are deadly conditions that can impact the functioning of the brain, heart, kidneys, liver, and perhaps more critically your guts.

While ischaemia and heat cytotoxity can be lethal by themselves, the set of physiological responses to those two attacks pose an even greater risk of death. For instance, breaking of the intestine lining due to the chemical assault from ischaemia and the thermal attack from heat cytotoxity, leads to the release of the gut content into the blood stream, which causes a third mechanism referred as “Systemic inflammatory response.” In this, the body triggers an inflammation that facilitates access of white blood cells to fight the infection. However, the same inflammation that allows for white blood cells can also facilitate further leakage of the guts and other organs whose membranes have been broken.

During all the internal mess created by ischemia, heat cytotoxity and the systemic inflammatory response, proteins that control blood clogging become overactive causing clots that can cut off blood supply to the brain, kidneys, liver and lungs; a mechanism called Disseminated Intravascular Coagulation. In turn, depletion of clotting proteins can lead to potentially fatal hemorrhaging even without injury. The final mechanism occurs when ischaemia and heat cytotoxity, compounded by extraneous activity (going on a hike, exercising, working outdoors, farming, etc), cause the breaking of skeletal muscle cells resulting in the leakage of myoglobin, which is toxic to the kidneys, liver and lungs.

“Dying during a heatwave is like a terror movie with 27 bad endings to choose from,” says Mora. “It is remarkable that humanity overall is taking such a complacency on the threats that ongoing climate change is posing.”

The paper further suggests that all heat damaging mechanisms can be triggered any time heat conditions are experienced, suggesting that anyone is at risk, with much greater risk for people with physical deficiencies or who cannot afford lifesaving tools, like AC.

In the paper, the authors comment that in the last decade, there has been >2300% increase in the loss of human life from heatwaves as a result of less than ?1°C warming. With 27 ways to die from extreme heat, the death toll that occurred with <1°C of warming emphasizes the heightened risk to human life even under the optimistic target of allowing the planet to warm up by another 1°C.

“Clearly, reducing the dangers of a warming world will require us to outperform even our most optimistic projections of climate change mitigation yet,” the authors conclude.

Abstract
Heat waves, sporadic events of extreme heat, pose a threat to human life. Deaths in excess of 70 000 people during the 2003 European heat wave, 10 000 people during the 2010 Russian heat wave, and high death tolls from numerous other heat waves1 are staggering demonstrations that extreme climatic conditions are already exceeding human thermoregulatory capacity. The area of the planet experiencing heat wave conditions similar to those that have killed people is expanding and is currently inhabited by ≈30% of the world’s human population.1 Because the planet will warm another 1°C by 2100 if we curtail greenhouse gases or 3.7°C if we do not, our choices for deadly heat are now between more of it or a lot more of it.1 Here we carried out a systematic synthesis of deadly heat physiological pathways to make the point that the human body is sensitive to heat and that heat waves can harm anyone (even the young and healthy2,3) in ways that extend beyond cardiovascular diseases. We suggest that only the rapid reduction of greenhouse gases paired with large economic investment in adaptation will help us escape the health risks of heat waves.

Authors
Camilo Mora, Chelsie W.W. Counsell, Coral R. Bielecki, Leo V Louis

IoL report
Science Total Environment abstract
University of Hawaii at Manoa material
www.hawaii.edu/news/2017/11/09/mora-heatwave-study/
Circulation: Cardiovascular Quality and Outcomes abstract


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