Heat waves and infectious gastroenteritis in US elderly, 1991-2004

The elderly population is more susceptible to gastrointestinal infections (GI) and may experienced more severe impact of hot weather then younger individuals. Several approaches has been developed to quantify the heat effects on human health, however the relations of hot weather on GI in elderly are not fully explored. We examined capability to predict seasonal fluctuations of GI-related hospitalizations using two measures of heat wave effects (HWE). The first measure is based on detection of exceedance of daily maximum temperature above 1.6 standard deviation compared to the 365-day moving average. The second measure records the exceedance of daily maximum temperature above 90ºF for three consecutive days. We compiled daily time series of HWE measures and rates of GI-related hospitalizations (ICD 9-CM 001–009, excluding Clostridium difficile: data were obtained from the Centers of Medicare and Medicaid Services) for 122 US cities during 14-year period, 1991-2004. Using time series analysis we determined the calendar day of peak timing for GI rates and HWE and demonstrated that the peaks of both heat wave indexes preceded the peak of GI hospitalizations. For example, in Chicago, Illinois we identified 54 and 35 events of heat waves (using both methods) and determined that their first incidence occurred on 180^th and 191^st calendar days, respectively, which are substantially earlier than the seasonal peak of GI rate (209^th ± 7.2). These preliminary results support the nation-wide effort to establish warning system of upcoming extreme weather effects to protect elderly population against heat exposure and preventable illness.