Canadians with cystic fibrosis have a median lifespan a decade longer than their U.S. counterparts and researchers on both sides of the border are trying to figure out why there's such a dramatic survival gap between the two countries.
A study found the median age of survival for Canadians with the inherited disease is almost 51 years, compared with about 40 years for their American counterparts.
After taking into account factors like patient age and disease severity, researchers found the risk of death among people with CF was 34 per cent lower in Canada than in the United States.
Cystic fibrosis, which is caused by a genetic mutation, causes thick mucus to build up in the respiratory system, leading to frequent infections that scar the lungs and reduce the ability to breathe. Mucus can also block tubes from the pancreas to the small intestine, requiring patients to take multiple digestive enzymes in order to absorb nutrients.
The study, published Monday in the Annals of Internal Medicine, was funded by the U.S. Cystic Fibrosis Foundation using data from 45,456 patients in its registry and 5,941 patients in the Canadian registry from 1990 to 2013. The 10-year difference in lifespan was based on data from the last five years.
"Survival has increased in both countries, but Canada began to see greater improvements than the United States starting in 1995, with an even more dramatic increase in the survival rate in Canada noted in 2005," said principal investigator Dr. Anne Stephenson, a respirologist at St. Michael's Hospital in Toronto.
"We don't know what the cause is, but we hypothesized that there are certain factors that may be contributing to the differences between the two countries."
One of them was Canada's adoption in the 1970s of a high-fat, high-calorie diet that resulted in patients being better nourished, said Stephenson, director of the Canadian Cystic Fibrosis Registry.
"If patients were born in that time period – the 1970s and '80s in Canada – they were exposed to good nutrition right from diagnosis or from birth," she said. "And they perhaps are benefiting from that early and long exposure to good nutrition. We know nutrition is definitely related to survival."
That diet, developed and tested at Toronto's Hospital for Sick Children, became the standard of care for CF patients in much of the world.
However, it wasn't adopted in the U.S. until about a decade after a Sick Kids' study showed that Toronto patients with CF had a better survival rate than those being treated at a comparable clinic in Boston.
"So we're thinking the effect of that may be a bit delayed in the U.S. because of the different approaches to nutrition in those early days," Stephenson said.
Erick Bauer of Toronto, who was diagnosed with CF at age five, believes he likely benefited from the bulked-up diet.
"As far back as I can remember, I've been on a high-fat diet and encouraged to eat as many calories a day as I can to maintain a stable weight," he said Monday.
Now 31, Bauer said his parents had been told at the time of his diagnosis that his health would likely deteriorate and he might not survive past age 16.
"I've been very lucky," he said, noting that as a child and teen, he had a relatively normal life, going to school and playing sports. It wasn't until he got into his 20s that he began having increased admissions to hospital to deal with infections that had severely reduced his lung function.
Bauer must take 50 to 60 pills a day – among them enzymes to aid digestion, anti-inflammatory drugs, antibiotics and vitamins – as well as continuing physical therapies that help control mucus build-up.
But he has not had to have a lung transplant, a rescue therapy for severely ill CF patients that Stephenson said may also play a role in the life expectancy gap between Canada and the U.S.
That may be because in 2005, the U.S. implemented an allocation score for prioritizing which patients would receive a lung transplant. It was at that time that the gap in the survival rate began widening even further.
That scoring system might have disadvantaged CF patients in favour of people with other advanced pulmonary diseases, she said. Canada uses a different allocation criteria, based more on doctors' subjective assessment of an individual patient's critical need for a transplant.
Lung transplantation is one of the few treatments that can improve survival almost immediately, and a higher proportion of CF patients received a transplant in Canada than in the U.S. during the study period, at a rate of 10 per cent to 6.5 per cent. Donor lungs do not carry the mutated CF gene, so the organs are not subject to the effects of the disease.
"Of the people who died, there were fewer people in Canada that died without a transplant compared to the U.S. data," said Stephenson.
Differences in health-care systems between the two countries might also affect the median age of survival, especially among U.S. patients without medical insurance, the researchers suggest.
"Canadians were 77 per cent less likely to die than people who are uninsured in the U.S.," she said. "(U.S.) Medicaid and Medicare together had a similar effect to Canadians, but not as dramatic. The people who indicated they had private insurance seemed to do as well as Canadians in terms of the risk of death."
In an accompanying editorial, Dr. Patrick Flume of the Medical University of South Carolina and Donald VanDevanter of Case Western Reserve University applauded the study, saying researchers now must find and implement solutions to bridge the survival gap, "which seems to be based on fundamental differences in the two nations' health-care systems."