Joyce Frieden is a freelance health and science writer in Rockville, Md.

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• NRC Reports on Similar Themes--Climate, Ecosystems, and Infectious Disease
• Health, Climate, and Infectious Disease: A Global Perspective [PDF]

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Better Data, More Biologists Studying Climate Effects Needed

Academy urges better data collection, a sharper focus on how climate affects human health, and improved interdisciplinary collaborations

Joyce Frieden

Although few would deny that climate can affect human health, past studies into climate-related effects have tended to be reactive. Thus, investigations of potential climate-related causes typically did not begin until after a disease outbreak occurred. Until recently, little in the way of proactive studies was undertaken, providing scientists with only primitive means with which to predict when a change in climate might lead to an outbreak of a particular disease.

With this in mind, the American Academy of Microbiology (AAM) convened a three-day colloquium late in 1999 to consider how better to tease out connections between climate and health, and to identify ways for encouraging researchers in climatology, biology, epidemiology, public health, and other disciplines to collaborate more effectively. The colloquium report, Health, Climate, and Infectious Disease: A Global Perspective, which was completed earlier this year, recommends several ways for meeting the challenges inherent in tying together these and other disciplines as a critical step toward improving climate-based public health predictions.

In a related development, the National Research Council of the National Academy of Sciences in Washington, D.C., recently issued a report on a similar theme, Under the Weather: Climate, Ecosystems, and Infectious Disease (see box, p. 353). Two contributors to the AAM report also contributed to the NRC report: Joan Rose, an AAM report author who is a professor in the College of Marine Sciences at the University of South Florida, St. Petersburg; and Robert Shope, a AAM colloquium participant, who is professor of pathology at the University of Texas Medical Branch's Center for Tropical Diseases in Galveston.

The Need for Better Data

While a great deal of meteorological data is now being collected, those data are not necessarily what is most needed by researchers investigating relationships between climate and health, according to the AAM report. "Say an entomologist wants to do a study on dengue fever"says colloquium participant Phil Arkin, program manager for climate dynamics and experimental prediction at the National Oceanic and Atmospheric Administration in Silver Spring, Md. "The transmission of dengue is related to how the virus grows in the mosquito, so it's related to both the mosquito population and viral behavior," which are both affected by local weather conditions.

In sizing up the situation, this prototypic entomologist well might figure that the most useful weather-related information for this analysis consists of knowing the amount of sunshine a particular area receives every afternoon because of its effects on how local mosquitoes feed. Although climatologists may have very good records of temperature and general weather conditions in such an area, information about incidental afternoon sunlight "is not something that's saved in the [meteorological] data sets" Arkin says. "There is an opportunity for people to determine what sorts of data would be the most useful, and to inspire the climatological community to regularly collect those."

The AAM report amplifies this point. "The health community should actively communicate to climatologists which data are of most value in developing models," it notes. "This should include both scale and specific parameters." Specifically, for the purpose of predicting particular disease patterns and the behavior of the pathogens that cause those diseases, the types of climatology data needed include direct measurements of specific sites, including those data that can be obtained by remote sensing methods, mid- and longer-term forecasts, and output generated by global climate models.

For example, access to mid- and longer-term climate forecasts could help local public health officials better allocate supplies of insecticide needed to forestall a potential vector-borne disease epidemic. In the United States, the establishment of firm links between climate projections, snow pack, and river runoff may allow a reasonably accurate forecasting of mosquito population size for the following summer and perhaps give officials a better means for estimating the seasonal prevalence of, say, St. Louis encephalitis.

Interdisciplinary Collaborations Are Challenging but Very Much Needed

Climatologists should improve their appreciation of what forecasts would be most useful to health researchers, the report continues. Collaborations between such specialists can be challenging, however, because scientists studying climate are unlikely to know on their own exactly what information would be most useful to public health specialists who are mandated to implement practical measures to safeguard the public. In turn, public health and other medical specialists are seldom familiar with the range of climate forecasts that may be available to them. "Improving this situation requires an iterative interaction between specialists in both fields," the AAM report notes.

Some progress is being made in this area, according to another colloquium participant, Jonathan Patz, who is director of the Program on the Health Effects of Global Environmental Change at Johns Hopkins University's Bloomberg School of Public Health in Baltimore, Md. "In the last decade or so, there's been a major surge in this type of research," he says. "A number of studies have given us a great new understanding of the relationship between weather and disease."

One phenomenon that helped researchers develop a better understanding of that relationship was the rise of El Niño, which gave many regions of the world very unseasonable weather, Patz says. As an example, he cites research done by his group to delineate a relationship between temperature and childhood diarrheal disease in Lima, Peru.

"So many things are seasonal, but you can't assume they're related to the weather," Patz explains. "The surge in diarrheal disease might [have more to do with] when the kids are in or out of school." But because El Niño brought with it an average temperature increase of 5° C in Lima during 1997 and 1998, the researchers could show a direct relationship between the temperature increase and a doubling of admissions for diarrheal disease at the city's largest pediatric hospital. "For every 1° C increase, we saw 8% more hospital admissions," he said. "It's hard to decipher long-term trends in disease, but we're beginning to understand that there's a strong relationship between climate factors and disease."

In fact, the El Niño phenomenon—also known as the El Niño Southern Oscillation, or ENSO-provided such a good opportunity for studying the effects of climate on health that the National Oceanic and Atmospheric Administration (NOAA) decided to spearhead El Niño-related climate research projects by microbiologists and epidemiologists. One large-scale result was the ENSO experiment, which enabled scientists to analyze connections between El Niño and malaria, dengue fever, encephalitis, cholera, and other diseases.

One difficulty in getting scientists from different fields to understand each other's needs is that they speak different scientific "languages," says Erin K. Lipp, a coauthor of the AAM report and a postdoctoral fellow at the Center of Marine Biotechnology at the University of Maryland Biotechnology Institute in Baltimore. "When climatologists talk about a ‘vector,’ they're talking about a mathematical concept—the relationship between rate, direction, and distance," she says. "But when biologists talk about a vector, we're talking about an animal or some type of host for infectious disease. Things like that come up a lot."

Climatologists and biologists also think differently when it comes to time and space, says Rose. "When we [biologists] talk about a disease or ecosystem, we're talking about the spatial scale of the niche of the mosquito; and when it comes to time, we speak in scales of weeks or months in terms of growth or the impact of climate change. Climate change, on the other hand, is in scales of months, and rain data is in scales of miles rather than a smaller geographical area."

To bridge such gaps, the report recommends fostering the growth of an emerging scientific field known as "bioclimatology." " There is a need to support such interdisciplinary training in bioclimatology, and this should be encouraged at all levels—including development of undergraduate courses, graduate programs that begin to merge the fields, and postdoctoral training grants," the report notes. There is also a need for meetings and journals in this burgeoning field—tasks that might best be accomplished by scientific societies, according to the report.

Near-Term Steps To Deepen Understanding of Climate-Disease Relationships

Nurturing the growth of bioclimatology will take time, but there are also steps that scientists can take immediately that would help to further define relationships between climate and disease. One such step would be to increase the amount of disease surveillance, which has been declining in recent years as the threat of some once-prevalent diseases has decreased. "It's the idea of institutional forgetfulness," Lipp says. "You put some type of surveillance system in place, looking for a particular pathogen, but after 10-20 years, everyone has forgotten why you started collecting the data to begin with."

Sometimes, officials might stop collecting data about a specific disease but then be caught unprepared when another outbreak occurs, she continues. "Once there's a problem again, people will say, ‘Why aren't we collecting these data?’" Disease surveillance also suffers from a constant funding shortage, according to Patz. "If we do a good job and prevent disease, soon the surveillance budgets shrink," he says. "Take the West Nile virus, for example. We simply have abandoned surveillance for encephalitis and tracking mosquitoes in many parts of the country, and now here we have this new outbreak. Of course, now the money is coming in. We're always in the reactionary mode rather than maintaining proactive surveillance."

The report paints a rather dire picture in terms of global disease surveillance efforts. "Throughout the developed world, systematic disease surveillance is being abandoned," it notes. "Therefore, while adequate historical databases are often difficult to obtain, there will soon be a lack of new consistent health statistics. . . . To advance our understanding of the relationships between climate variability and infectious diseases, the following data are needed. Long-term, historical disease and pathogen surveillance data must be located, salvaged, and electronically archived. Continuing emphasis should be placed on prospective long-term surveillance that includes medical, ecological, and climatological parameters at periods greater than five years."

Surveillance is an area where a multidisciplinary approach is needed, according to Shope, a colloquium participant and professor of pathology at the University of Texas Medical Branch's Center for Tropical Diseases in Galveston. "Surveillance studies should be done by health care workers in collaboration with people who understand climate and climate change, and people who are able to model what's happening in the climate and link that to people who are able to model what's happening in infectious diseases," he says. "The long-term aim ought to be to understand enough about those links to predict what's going to happen. We can't do it now because we don't have the information."

Predictive abilities like that would certainly have been useful during the last El Niño event, says Arkin. "In 1997-98, there was an epidemic of Rift Valley fever in Africa, which was clearly related to changes in rainfall that occurred during El Niño. Had people known what the rainfall changes were going to be, they would have had a much better chance of predicting the epidemic. And better forecasts have the potential to permit better preparation and all sorts of public health measures that would be useful."

Health Sector Assessment

Rain projections would also help predict disease outbreaks even in the United States, which is thought to be more protected because of its infrastructure and wealth, Patz says. "There are about 950 communities in the U.S. which still have combined sewer systems, where they combine their storm water with their sewer water," he says. "If it rains too heavily there, you're going to have a spillover of sewage into the surface water. We still do not have perfect water systems; they are at risk, especially when you have flooding events." (Patz's research into the area of groundwater contamination and its relationship to health is part of an assessment on the health impacts of climate change in the U.S. The assessment, which was mandated by Congress and sponsored by the U.S. Environmental Protection Agency, can be viewed online.)

Better Guidance Needed To Direct Surveillance Efforts

Of course, even having consistent disease surveillance data does no good if researchers are not looking for the right things, says Lipp. For example, while studying the Charlotte Harbor estuary in Florida during El Niño, she and a colleague noticed that, with increased wet weather from the event, 75% of the water stations they looked at contained enteric viruses— and most of those places had never contained such viruses before. "Currently, people use fecal coliform levels to indicate whether or not the water body is safe," she says. "If we had used that test, we would have found the water safe, and yet we were finding viruses in it." Those viruses were found in areas where the major method of wastewater disposal was septic tanks, she points out.

Problems like this will affect more than drinking water, according to the AAM report on climate change and disease. "Food products, including seafood, may also be contaminated with enteric pathogens during handling, while fruits and vegetables may become contaminated with poorly treated irrigation waters," it notes. "For enteric pathogens, fecal indicator species are often used to determine the level of contamination but are ineffective as a proxy for naturally occurring pathogens, which may be more susceptible to climate variability." The report calls for the creation of a global climate model for analyzing its effects on specific pathogens, as well as the development of methods to identify emerging and specific pathogens to determine their persistence, survival, and distribution in the environment.

There is another reason for continued disease surveillance, according to the report: the threat of bioterrorism. "Agencies must be able to differentiate between ‘natural events’ that happen under appropriate and understandable conditions and those not likely to occur in the context of changing or variable climate patterns," according to the report. "In either situation, introduced pathogenic or vector organisms may potentially become endemic in novel areas under the appropriate set of environmental and climatic factors. It is critical at this time of increasing world travel and threats of bioterrorism that active surveillance programs for pathogens, diseases, and climate variables are implemented and continue."

Patz hopes that the emergence of bioclimatology will make members of the public and policymakers understand the complex relationship among health, global warming, which may be partly caused by human activity, and climate in a broader sense. "By figuring out linkages between climate, ecology, and health, hopefully we'll begin realizing environmental policy is the same thing as public health policy, and continue to move upstream," he says.