By LEE BOWMAN
Scripps Howard News Service
January 21, 2010
The science is fairly well established on links between extreme cold and heat and increased risks for heart disease, frostbite, heatstroke and infectious diseases like flu.
And the more direct effects of weather on injury are clear enough -- the hurricane-blown tree that falls on a car or drowning in a flash flood.
Deaths and injury less directly tied to a storm can be harder to categorize: the chain-saw accident that claims fingers weeks after a tornado, or carbon-monoxide poisoning from an improperly positioned generator.
Medical researchers are finding that weather conditions also have a more subtle, indirect impact on other illnesses, from asthma to ear infections to appendicitis.
For instance, researchers in Detroit reported last fall that changes in humidity and temperature can drive more children with asthma to the emergency room for up to five days after the weather shifts.
The study, led by Dr. Nana Mireku at Children's Hospital of Michigan, matched more than 25,000 visits by children for asthma flare-up over a two-year period with data on weather, pollution and allergen levels.
After taking into account pollutants and airborne allergens, "We found a strong correlation between temperature and humidity fluctuations with asthma fluctuations, but not barometric pressure, '' she said, adding that it is one of the few studies to consider that weather a few days before an asthma flare-up is as important as the weather on the day of admission to the emergency room.
Right now, National Institutes of Health guidelines merely list a "change in weather" as a possible precipitating factor for asthma, but offer no detailed guidance.
Mireku, now an allergist in Dallas, said knowing that increases in humidity and temperature both drive up emergency admissions can help doctors and patients develop better treatment plans to prevent the sudden worsening of airway inflammation.
Another study, reported last spring by researchers in Boston, found a connection between higher temperatures and lower barometric pressure on people coming into an emergency department for a headache, but did not find a link to pollution levels.
However, weather conditions that worsen pollution, such as very hot days with stalled air masses over cities, still may matter for certain conditions, particularly the lungs, but so do overall efforts to reduce pollutants.
A team of ear specialists reported last fall that they found a link between reduced pollution levels over a decade in many cities and a decline in the percentage of children suffering from three or more middle-ear infections within a year.
Then there's appendicitis. One report from Canadian researchers last fall found that most admissions for severe inflammation of the appendage come between April and September, the warmest months of the year in Canada, and a time when more people are likely to be outside.
Zeroing in on air pollutants in Calgary, Alberta, the researchers found that high levels of ozone and nitrogen dioxide accompanied higher incidence of appendicitis, particularly among men. The scientists suspect that some pollutants trigger an inflammatory response not just in the lungs, but also in other organs including the gut.
Another study, published just this week by researchers at the University of Texas Southwestern Medical Center, documented some seasonal trends, with a slight uptick during the summer.
The senior author, Dr. Edward Livingston, said the seasonal variation of appendix flare-ups, and clustering of the cases in certain years, suggests that appendicitis may be driven by some periodic surge in viral infections.
Appendicitis, which has only been diagnosed for about 120 years, appears to be more prevalent in countries that become more developed and industrialized, and some scientists think a decline in this country over the past 25 years has been at least in part due to pollution controls.
Livingston's team noted that several spikes in appendicitis cases during the 1990s suggest other things drive the condition, which traditionally results in emergency surgery to remove the infected organ before it bursts. The Southwest team says its research into trends between 1970 and 2006 also suggests that emergency surgical removal may not always be needed or produce the best outcome.
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