Does severe flooding increase the incidence of gastrointestinal illness? An analysis of three data collection methods during a severe flood of the Mississippi River in 2001

Recent studies have demonstrated an association between severe precipitation and outbreaks of waterborne disease. Because the most frequently observed manifestation of waterborne disease, gastrointestinal (GI) illness, is common, moderate increases may be difficult to identify. Few studies have examined the impact of severe weather on endemic GI illness.; Flooding occurred in the Midwestern United States in 2001. Since November 2000, GI symptoms have been collected on 1,296 subjects in the Water Evaluation Trial (WET). The WET cohort is located near Davenport Iowa, which was severely impacted by flooding. GI illness has also been monitored using a random digit dial (RDD) telephone survey, and diagnoses of GI illness at health care facilities.; Objectives of this investigation were to: (1) determine whether rates of GI illness were elevated during the flood; and (2)determine whether contact with flood water was associated with an increased risk of GI illness. Secondary objectives were to contrast the results from three surveillance methods and describe the incidence of GI illness. GI illness in the WET cohort and the RDD survey peaked in winter and was lowest in summer and early fall. Diagnoses of GI illness were low in winter and peaked in early spring. Yearly rates of GI illness were 2.33 (95% CI 2.21--2.44) from the WET cohort and 1.47 (95% CI 1.30--1.66) from the RDD survey.; An increase in the incidence of GI illness during the flood was observed in the WET cohort (IRR = 1.24, 95% CI 1.04--1.47), and this effect was pronounced in those susceptible to GI illness. GI illness rates from the RDD survey did not increase, and physician diagnoses were lower during the flood. The results suggest that an increase in the incidence of GI illness that did not result in a visit to a health care provider occurred during the flood. This conclusion is based on the consistency of the WET data, which were the most rigorously collected.; Both the WET cohort and the RDD survey supported an association between GI illness and contact with flood water. This risk was elevated in children 12 years and under. Children with flood contact had rates of GI illness 1.9 times (95% CI 0.93--3.85) those without flood contact, resulting in 651 estimated excess cases of GI illness in the community.; Future research on infectious disease transmission following natural disasters should focus on susceptible individuals. Other research should address the validity of surveillance methods and definitions of GI illness. Standardized surveillance for GI illness and other common syndromes can help quantify health impacts of natural disasters.