Individuals affected by a breakout of E. coli O157:H7, such as the infamous Walkerton incident more than a decade ago, display no evidence of any increase in cardiovascular disease, which had originally been the thought, according to Western-led study.
Shiga toxin is produced by E. coli O157:H7, which can damage the small vessels of the kidneys and lead to high blood pressure. That same toxin can directly damage the larger systemic blood vessels throughout body. The infection also triggers an inflammatory response, which may not entirely resolve in some people, leading to chronic inflammation and the formation of atherosclerosis, or plaques in the blood vessels, putting people at higher risk of events like heart attacks and strokes.
Entitled Cardiovascular disease after Escherichia coli O157:H7 gastroenteritis, which recently appeared in the Canadian Medical Association Journal, the study is part of a larger series of studies examining the long-term health outcomes in Walkerton, said Patricia Hizo-Abes, a third-year Schulich School of Medicine & Dentistry student in the Windsor program. She took part in the study through the Summer Research Training Program (SRTP) at Schulich.
“We wanted to know whether the degree of illness at the time of the outbreak was related to the development of cardiovascular disease 10 years later,” said Hizo-Abes, who is pursuing Family Medicine. “Our approach was quite different from previous studies.”
Looking to determine more accurately the 10-year risk of death and cardiovascular events like heart attacks and stroke, the Western-led study compared 898 adults in Walkerton to a group of more than 11,000 residents living in the surrounding communities who weren’t affected by the outbreak. Health-care databases that track these events (like the Ontario Health Insurance Plan and the Canadian Institute for Health Information) were used rather than relying on participants’ recalled reports.
Hizo-Abes said the team hypothesized individuals most severely affected by the outbreak would have an increased risk of cardiovascular disease and death after 10 years. This was based on previous findings of increased kidney dysfunction, hypertension and self-reported cardiovascular disease in the people that became ill.
The study showed no deviation between the affected community and the general population. Simply stated: E. coli did not cause any increase in cardiovascular disease.
“We expected to find a correlation, but when we did not, we were not surprised. By virtue of participating in the Walkerton study, participants received extra health care, screening and treatment for hypertension and kidney disease,” said the 25-year-old Mississauga native. “These risk factors for cardiovascular disease often go untreated in the absence of active surveillance, so diagnosis and treatment of these conditions may have been greater for Walkerton participants compared with people in the surrounding communities.”
While the study’s findings may not be a definitive conclusion, it does offer some reassurance.
“In our particular study, the Walkerton participants were followed closely by health-care professionals for years and were treated for hypertension and kidney disease, likely preventing cardiovascular disease,” she said. “Had they not had the same surveillance and treatment, it is difficult to say whether the results would have been different. Further research in this area is needed to draw any definitive conclusions.”
While uncommon for undergraduate students to play a role in a major research paper, Hizo-Abes credits her two-year involvement with SRTP for the opportunity. The program enables first- and second-year medical students to work under faculty supervision on a research project during the summer months, for two years. She worked with Western Epidemiology & Biostatistics professor Amit Garg.
“I was ecstatic and so fortunate to be part of a study of this calibre at this stage of my training. I think it’s pivotal that medical students are given the opportunities to be part of cutting-edge research at the beginning of our careers,” she said. “We can contribute a fresh perspective on a problem while we are still developing an understanding of novel concepts; our thinking has not yet become so conventional.
“It is actually the experience of designing, writing and collaborating on a study like this that gives me an advantage, much more so than having my name on a paper in a prestigious journal.”