February 1997
NEW YORK —The weather affects every physician's practice. But how much attention do most physicians give to the larger issue of climate change and its relationship to health?
A Johns Hopkins researcher questioned whether the full significance of climatic factors upon the incidence of asthma, allergies and infectious diseases has been adequately appreciated. "I would argue it has not been considered enough," said Jonathan Patz, MD, MPH, director, Program on Health Effects of Global Environmental Change, department of environmental health sciences, the John Hopkins School of Public Health, a new program at Hopkins.
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At a recent conference here, scientists from the Environmental and Occupational Health Sciences Institute at Rutgers University called for the establishment of a National Institute for the Environment (NIE), which would consider the environmental influence on diseases.
David E. Blockstein, Bernard D. Goldstein and Mark G. Robson of Rutgers presented this recommendation because of possible links between the increasing incidence of infectious disease and environmental change. The proposed institute would not have a regulatory role. Congress is considering legislation to create the NIE.
Patz does not want to exaggerate nor underestimate the significance of climate on asthma, allergy and infectious diseases. "Climate is only one issue among many, but it is an important one. We are not necessarily speaking of how climate directly affects diseases, for the impact of climate manifests in a number of ways."
For example, it affects the migration habits of animals and insects, the growth patterns of vegetation, malnutrition due to climate stress on agriculture, urban migration, urbanization and increased ultraviolet radiation. "The bottom line is that some diseases may change geographic distribution," and physicians may not consider them in their differential diagnosis. For example, malaria spread into New York and New Jersey in 1991 and 1992 during unseasonably hot summers, noted Patz, who spoke here at the 124th Annual Meeting of the American Public Health Association.
"Physicians need to be aware of some diseases showing up where they don't usually appear," he pointed out, citing the appearance of dengue in the South and malaria in the North. Dengue's appearance in Texas in 1995 occurred during an unusually warm year, he said.
If areas of the country where malaria had previously been rare were to become suitable for the spread of the disease, it might be prudent to take preventative measures; for example, mosquito vector control and draining water close to houses. It also might make sense to avoid open water systems, which are breeding grounds for mosquitoes.
"Global warming may lead to an increased incidence of allergies and "asthma related to photochemical urban smog," Patz said, while strongly cautioning that "asthma is tough to model and actually figure out. Increased incidence of asthma in the United States has been noted but not yet adequately explained.
"It is possible that the indoor environment plays more of a role than climate changes, but no one knows," he said.
Urban smog should continue to be studied for its effects on asthma. Referring to global warming, he noted that the ozone is "a significant pulmonary irritant." However, ozone's actual effects upon asthma is unknown.
Ozone is not the only way climate may affect asthma. Pollen is often implicated in allergies and asthma. Several climate models indicate an increase in precipitation in the eastern United States, which will probably increase vegetation. Subsequent increases in pollen levels may affect the incidence of allergies and asthma.
Climate impacts asthma in other ways. "We have no idea what the effects of climate change would be," Patz said. Global warming might, he speculated, have positive consequences for asthma induced by cold weather.
It is possible that even while ozone and pollen are adversely affecting some asthma patients, cold-induced asthma might be helped by a warmer climate, he said, mentioning work by Laurence Kalkstein, PhD, of the University of Delaware who has been studying this relationship. "All this needs to be examined," he said. "Each of these parts is only one small part of the story.
"While current pediatric health crises remain a priority, we must not lose sight of potential long-term hazards, such as climate change. These may be insidious and are likely irreversible," Patz said.
Better understanding the role of climate in the transmission of infectious diseases will require interdisciplinary cooperation, he suggested, saying that epidemiologic analysis must be augmented by integrated mathematical modeling. In addition, geographical data systems and satellite remote imaging may provide important analytical tools, he said.
"The character of the public health infrastructure helps to determine where the disease is seen," Patz said. "This is one of several issues where environmental policy actually becomes public health policy. If climate has been shown to be influenced by human activity, as an intergovernmental panel has concluded, then we need to integrate environmental and public health policy."
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