It’s difficult to identify an area of public health that will not be affected by climate change, Dr Jeremy Hess from the University of Washington told the ATS meeting.
“The direct effects of climate change include increased heat stress, floods and drought, and more intense storms,” he said.
“Indirect effects include worsening of air pollution, wider spread of disease vectors including mosquitoes, food insecurity and under-nutrition, displacement of populations, and effects on mental health.”
Seasonal patterns of common respiratory diseases such as influenza provide a clear example of the links between climate and health.
“Many other diseases are sensitive to temperature, rain, humidity and sunlight exposure,” Dr Hess said.
“However, ‘climate’ is a defined by patterns over 30 years or more, so assessing the interactions between climate and health is complex. It’s more pragmatic to say that a disease is ‘climate sensitive’.”
While influenza is more common in winter in temperate climates, flu epidemics tend to be more persistent in tropical regions and more common in humid or rainy seasons. “Some of these local dynamics may become more favourable with climate change, rather than worse, but there is no question that the patterns will change,” Dr Hess said.
Climate-sensitive viral infections also include respiratory syncytial virus and hantaviruses. The seasonality of hantavirus is probably mediated through the effect of seasons on the activity of rodents which who carry the disease.
Bacterial infections are generally less climate sensitive, but those with some seasonal variation include tuberculosis (occurring mainly in winter), Legionella and pneumonic plague (also affected by the numbers of rats as vectors).
Pneumonia caused by S. pneumoniae and other bacterial pathogens often has a seasonal pattern, but this might be driven more by the patterns of viral infections which can predispose to them. “Bacterial pneumonia tends to be more seasonal in developing rather than developed countries,” Dr Hess said.
Fungal infections are increased by higher moisture and temperature. Coccidiomycosis is the prototypic climate-sensitive fungal respiratory pathogen, and the cause of valley fever. In the United States it is generally restricted to the south-west, including California, but its range is spreading.
“We have just had the first case reported in Washington state,” Dr Hess said. “There is also a distinct ‘grow and blow’ pattern, in which the fungus prospers during wet seasons but is then dispersed widely by wind in times of drought.”
Public health experts are central to understanding interactions between respiratory disease and climate change.
“The first step is to analyse changes in climate and disease in the past,” Dr Hess said.
“The second step is to continue careful surveillance of current changes in the pattern of disease. The third is to develop predictive scenarios about possible changes in the future, and how best to respond.”