By Kelly A. Reynolds, MSPH, PhD
Symptoms of irritable bowel syndrome (IBS) include cramping, abdominal pain, bloating, gas, diarrhea and constipation. The disorder tends to be chronic with recurrent episodes over time. IBS impacts up to 20 percent of the US adult population. The overall cause of IBS appears to be related to abnormalities in the intestinal lining or the gastrointestinal nervous system. Reportedly, specific foods exacerbate IBS symptoms. Stress and hormonal changes, particularly seen in women, may also worsen symptoms. Additional risk factors include exposures to microbial contaminants leading to gastroenteritis or diarrhea. Given that enteric pathogens can be spread by the waterborne route, IBS is, therefore, an indirect result of contaminated drinking water.
Risk factors for IBS include both genetic and environmental variables. Being under the age of 45, having a family history of IBS or other stress, such as abuse, anxiety or depression, are all recognized risk factors. Long-term effects of IBS are generally related to reduced quality of life, rather than a more severe adverse health outcome. Treatment is limited and involves experimenting with avoidance of food triggers, increased fluid intake, exercise and relaxation therapies.(1)
Although the causes of IBS have not been comprehensively identified, a link to microbial infections has been definitively established. Between five and 30 percent of people experience chronic gastrointestinal symptoms following a previous bacterial infection, even after infection has cleared.2 Chronic effects may be due to lingering inflammation, damage to the permeability of the gut wall and changes in neuromuscular function of the gut. Knowledge is lacking, however, as to the long-term prognosis of individuals who chronically suffer from post-infection IBS (PI-IBS).
In 2000, an outbreak occurred in Walkerton, Ontario, a small rural community served by a municipal water supply. Walkerton had a population of ~5,000 people at the time. Spring rains were credited with increasing the fecal runoff from local animal farm operations in shallow well-water sources.3 Coupled with inadequate chlorination, an outbreak was born. Nearly half of all residents experienced adverse symptoms from exposure to E. coli O157:H7 and Campylobacter, both enteric pathogens causing mild to severe diarrhea and gastroenteritis. In total, 2,300 cases of acute gastroenteritis, 750 emergency room visits, 65 hospital admissions, 27 cases of severe haemolytic uraemic syndrome (HUS) (a deadly disease often leading to hospitalization due to red blood cell destruction, bloody diarrhea and acute kidney failure) and seven deaths were attributed to the outbreak.(4 )The Walkerton Health Study was initiated to evaluate long-term health outcomes and track PI-IBS in a population involved in this wellknown waterborne disease outbreak.
Two years after the massive Walkerton waterborne outbreak, The Walkerton Health Study began looking at the long-term health effects of the event.5 More than 4,500 subjects living in Walkerton at the time of the outbreak volunteered in 2002 or 2003 for annual health assessments at a local clinic. All participants were 16 years or older and were tracked for the next six years. Assessment goals were to evaluate the prevalence of PI-IBS in the community. None of the participants selected for the study reported any prior history of chronic gastrointestinal disease but they were divided into three groups based on whether they 1) had no illness during the 2000 outbreak; 2) did report experiencing illness during the 2000 outbreak without medical documentation or 3) did report experiencing illness during the 2000 outbreak that was also validated by medical records with a category of clinically suspected gastroenteritis. Categories two and three provide evidence of the severity of the acute illness as best can be determined objectively.
Next, researchers identified which of the subjects in each exposure group was diagnosed with IBS after four, six and eight years post-infection. Of those who suffered symptoms in the 2000 outbreak, 28.3 percent (210/742) were also determined to have IBS two to three years later. After four years, the IBS prevalence rate decreased to 21.4 percent (159/742) and further after six years to 14.3 percent (106/742). At the end of the longitudinal study (eight years post-infection), 15.4 percent (114/742) of the Walkerton population exposed in the outbreak were still suffering from chronic IBS.6 Residents at the time of the Walkerton outbreak who were not sickened experienced IBS at a rate of 5.4 percent (114/742) eight years later.5 In the sickened group, PI-IBS symptoms waned over time; however, one in seven patients (14 percent) were still suffering from IBS eight years post-outbreak.
Waterborne disease in the US is usually self-limiting but may still have long-term deleterious effects. Recognized bouts of acute waterborne disease do not fully represent the havoc that such microbial exposures wreak long term. Acute symptoms of waterborne outbreaks can be severe, resulting in hospitalization with long-term complications or even death. For those who do not experience such severe outcomes initially, recognition of lingering health complications is lacking. The Walkerton tragedy provides a means for evaluating long-term consequences from acute microbial exposures, increasing the concern over the quality and protection of drinking water supplies. Approximately 10 percent of IBS patients can trace their onset of symptoms to a previous episode of infectious diarrhea.7 Globally, the World Health Organization estimates between two and four million cases each year resulting in a significant burden for both the developed and developing world. In addition to the strong evidence of long-term effects associated with PI-IBS, Walkerton residents also had a 33-percent relative increase in risk of hypertension if they experienced severe gastroenteritis during the outbreak, accompanied by reduced kidney function and increased risk of self-reported cardiovascular disease and arthritic symptoms four years post-infection.(4), (6)
Self-limiting diarrhea is generally of mild concern following exposure to waterborne microbial contaminants and mortality rates tend to be low in the US. Diarrhea, however, is not the only concern. Long-term human health effects post-infection are being increasingly realized. Preventing exposure remains the best defense for human health. Given the vulnerability of municipal water supply contamination and treatment inadequacies, POU filtration devices rated for microbial removal continue to provide effective treatment at the tap against both acute and chronic waterborne diseases.
- Mayo Clinic Staff, Irritable Bowel Syndrome, Mayo Foundation for Medical Education and Research, 2014. [Online]. www.mayoclinic.org/diseases-conditions/irritable-bowel-syndrome/basics/definition/CON-20024578
- Marshall, J.K.; Thabane, M.; Garg, A.X. et al. “Intestinal permeability in patients with irritable bowel syndrome after a waterborne outbreak of acute gastroenteritis in Walkerton, Ontario,” Alimentary Pharmacology Therapeutics, vol. 20, no. 11-12, pp. 1317-1322, 2004.
- Anon., The investigative report of the Walkerton outbreak of waterborne gastroenteritis, Bruce-Grey-Owen Sound Health Unit, 2000.
- Clark, W.F.; Macnab, J.J. and Sontrop, J.M. on behalf of the WEL Investigators of the Walkerton Health Study, The Walkerton Health Study 2002-2008 Final Report, London Health Sciences Centre, London, Ontario, 2008.
- Marshall, J.K.; Thabane, M.; Garg, A.X. et al. “Eight year prognosis of post-infectious irritable bowel syndrome following waterborne bacterial dysentery,” Gut, vol. 59, pp. 605-611, 2010.
- Beatty, J.K.; Bhargave, A. and Buret, A.G. “Post-infectious irritable bowel syndrome: mechanistic insights into chronic disturbances following enteric infection,” World Journal of Gastroenterology, vol. 20, no. 14, pp. 3976-85, 2014.
- Clark, W.F.; Sontrop, J.M.; Macnab, J.J. et al., “Long term risk for hypertension, renal impairment, and cardiovascular disease after gastroenteritis from drinking water contaminated with Escherichia coli O157:H7: a prospective cohort study,” The British Medical Journal, vol. 341, no. c6020, 2010.
About the author
Dr. Kelly A. Reynolds is an Associate Professor at the University of Arizona College of Public Health. She holds a Master of Science Degree in public health (MSPH) from the University of South Florida and a doctorate in microbiology from the University of Arizona. Reynolds is WC&P’s Public Health Editor and a former member of the Technical Review Committee. She can be reached via email at email@example.com