Weathering Diarrheal Illness.

Effects of El Nino in the South Pacific

In recent years, researchers have been investigating links between climate variation and diarrheal diseases. In two recent studies reported this month, Reena B. K. Singh of the Wellington School of Medicine in New Zealand and colleagues at the International Global Change Institute and the World Meteorological Organisation find a positive relationship between rising average annual temperatures associated with the El Nino climate phenomenon and diarrheal disease reports in 18 Pacific Island countries between 1986 and 1994 [EHP 109:155-159].

Sources of fresh water in the Pacific Islands are few. The "high islands," such as the Hawaiians, can depend on more regular rainfall because their mountain peaks cool passing clouds, wringing moisture from them. The "low island" atolls, usually arranged on doughnut-shaped coral reefs that once ringed volcanic mountains that have since eroded away, also depend on rainfall for water. But without mountains to encourage rainfall, less land mass than the high islands, and closer proximity to the ocean, they have minimal freshwater collection and storage capability and a higher likelihood of saltwater contamination during storms.

In either case, drinking water supplies in the Pacific Islands are both precious and precarious under the best of circumstances, and are growing more so all the time. Because many Pacific Islands depend on stored rainwater for drinking and hygiene, variations in rainfall and temperature affect their supplies in ways that increase the likelihood of contamination with fecal matter or bacteria or the need to resort to contaminated supplies--and contaminated water is a frequent cause of diarrheal disease. In addition, rising global sea levels and flooding from rain and high waves may also compromise supplies with both sewage from sanitation systems and saltwater, which can itself cause diarrhea.

In the first study, Singh and colleagues obtained data on Pacific Island diarrhea cases, population, land area, and precipitation rates from various sources. They then compared data on the average annual diarrhea caseload, gross national product, temperature, and water availability for the period 1986-1994. The second study used monthly reports of Fijian infant diarrhea for the years 1978-1998 along with temperature and rainfall data to generate predictions of diarrhea reports for the years 1993-1998.

The researchers found that three low-lying atoll nations--Tokelau, Tuvalu, and Kiribati--had the highest average annual temperatures, the lowest potential water availability, and the highest average rates of diarrhea during the study period. In contrast, the nation of Nauru also suffered high temperatures, yet enjoyed the lowest diarrhea rate, probably due to a more robust economy capable of paying for water purification. Analysis showed that higher gross national product was associated with lower diarrheal disease rates among all the nations studied, regardless of rainfall.

A more detailed analysis showed that low rainfall was associated with increased diarrheal disease reports in the same and following month, while high rainfall was associated only with increased diarrheal disease in the same month. The researchers suggest that low rainfall and high temperatures may contribute to simultaneous food spoilage and reduced hygiene, while high rainfall would be more likely to lead to short-term contamination from flooding followed by a period of improved water quality.

The authors conclude that improved water storage facilities, better sewerage and sanitation, and increased provision of primary health care will all be necessary to help the Pacific Islands adapt to climate changes that result in higher temperatures and changes in rainfall patterns.