Inflammatory Bowel Disease: Heat Waves Linked to Flares

Joanna Broder

August 13, 2013

During a heat wave, there is more to worry about than just heat stroke: Flares of inflammatory bowel disease (IBD) and bouts of infectious gastroenteritis (IG) are things to consider as well, according to a study from Zurich, Switzerland, published online August 13 in the American Journal of Gastroenterology.

"There is evidence for an increase of IBD hospital admissions by 4-6 percent for each additional day within a heat wave period," Christine N. Manser, MD, from the Division of Gastroenterology and Hepatology, Department of Internal Medicine, University Hospital, Zurich, and colleagues said in a new release. "Presence of a heat wave was estimated to increase the risk of [IG] by 4-7 percent for every additional day within a heat [wave] period. In the control group there was no evidence for a heat wave effect."

To conduct this retrospective, controlled observational study, researchers used data from 738 patients with IBD and 786 patients with IG who had been admitted to a Swiss hospital during the 5-year period from 2001 to 2005. They then compared this data, using other noninfectious chronic intestinal inflammations as the control. The Swiss Federal Office for Meteorology and Climatology provided climate data for 17 heat waves during the same period.

Results from the study showed that for every additional day within a heat wave, the risk for IBD flare ups increased by 4.6% (95% confidence interval [CI], 1.6% - 7.4%; P = .0035), and the risk for IG flares increased by 4.7% (95% CI, 1.8% - 7.4%; P = .0020). Members of the control group, in contrast, showed no significant effect (95% CI, −6.2% - 2.9%; P = .53). The analyses were adjusted for day of the week, long-term time trends, and seasonal pattern.

Results also suggest that the risk for IG increased per day and was strongest "when lagged by 7 days" (risk increase per day, 7.2%; 95% CI, 4.6% - 9.7%; P < .0001). The risk for IBD did not require such a transformation: The model fit was not improved by using formulations that had additional adjustments for daily average temperature, the authors note.

"[W]e found a substantial increase in hospital admissions because of flares of IBD and IG during heat wave periods," they write. "Whereas the effect on IG is strongest with a delay of 7 days, the effect on IBD flares is immediate, suggesting different mechanisms."

One of the reasons heat waves might affect IBD flare-ups and IG is because they can cause physical stress, Dr. Manser said in the press release. "Physical as well as mental stress has been shown to cause flares of IBD and may explain the increase in IBD hospital admissions during heat."

The growth of bacteria may be another factor affecting how heat waves affect digestive symptoms, the authors write. "During a heat wave, changes in bacterial composition of food, skin, soil, and water may occur. This has never been investigated in much detail. However, recent research suggests that temperature plays a crucial role for the expansion of enterohemorrhagic Escherichia coli and other pathogenic bacteria," they write.

"This study ties heat stress to digestive symptoms supporting the observed seasonal variation in the clinical course of [IBD] and suggests that microbial infections of the gut might be additionally influenced by climate changes," Dr. Manser said in the news release.

In conclusion, the authors warn that the public should be aware of an increased risk for flare-ups from IBD and IG during a heat wave. "[M]itigation and adaptation strategies are needed to reduce current vulnerability to climate change and to address the health risks projected to occur over the coming decades," they write.

This study was supported by the Swiss National Science Foundation. The authors have disclosed no relevant financial relationships.

Am J Gastroenterol. Published online August 13, 2013. Abstract

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