Associations between temperature, excessive heat events, and infectious gastroenteritis in US elderly

Elderly are susceptible to the adverse health effects induced by excessive heat events (EHE), however, the association between EHE and gastroenteric illnesses is unclear. Hospitalization records in 1991–2004 involved gastrointestinal infections (GI: ICD 001–009 except Clostridium difficile) and symptoms (GS: ICD 558.9 and 787) in patients of age ≥65 were obtained from the Centers of Medicare and Medicaid Services and merged with daily maximal temperature from the National Climate Data Center in 16 metropolitan cities. Times to peak of the hospitalizations and temperature were determined using annual harmonic regression and contrasted. An EHE is defined as daily maximal temperature exceeding 90th–98th percentiles based on the 14-year long distribution. The resultant binary indicators were transformed into continuous exposure variables in order to carry over the “heat effects” across different incubation periods ranging from 1–40 days. In the 16 cities, annual rates of GI and GS were 11.9±1.31 and 140.4±8.9 cases per 10,000 elderly. They peaked around February and March, 15 days apart (GI: 45th±4 days; GS: 60th±4 days; r=0.66, p<0.01), while temperature peaked in August (205th±2 days). Despite such antiphase, on average, an EHE was significantly associated with an increase in GI-related hospitalizations by a factor of 1.24–5.95 in the following 11–38 days (p<0.05). For GS, all 16 cities demonstrated a positive association: hospitalizations increased by a factor of 1.10–1.42 over the 15–40 days after an EHE (p<0.01).