The patients had survived childhood cancer, gone through chemotherapy and left in generally good health. But every winter they were showing up again in hospital beds and emergency rooms across Utah, unable to breathe.

Their doctors were confused.

What was making these kids who had overcome some of the worst illnesses — leukemia, tumors, lymphoma — so sick? Why was it affecting only their lungs when they didn’t have breathing problems before? And what was it about this particular group of survivors in this time of year?

For more than three decades, the trend continued. Most oncologists in the state knew about it, swapped stories and shared data with one another that they had observed in following up with their cancer patients. They didn’t have a bigger explanation, though, for the new symptoms and they didn’t know what to do about it, so it went largely unreported.

On Tuesday, researchers announced a first of its kind study and what they believe is the culprit behind the unusual correlation: air pollution.

“It turns out childhood cancer survivors are more susceptible to bad air quality,” said Douglas Fair, a pediatric doctor at Primary Children’s Hospital, located on campus at the University of Utah. “It just speaks to a larger picture of things.”

The research, conducted at the U. and led by the Huntsman Cancer Institute, found a strong connection between those who had survived childhood cancer and those being hospitalized for breathing problems. Most of the episodes, the study found, came within three days of a major bad air event — primarily inversions, which impact the Salt Lake Valley in the winter months.

Kids who had undergone chemotherapy and radiation to treat their cancer were typically impacted even more.

“Some don’t have full immune function after that,” said Judy Ou, the lead author on the study and an institute researcher. Their lungs, she added, are still developing in childhood and can be weakened by treatment and cancer in general.

Overall, those cancer survivors were found to be roughly two times more likely than other kids to be affected by the air quality and develop a respiratory illness, such as pneumonia or bronchitis. That’s about the same rate for those with asthma or heart conditions, who are already considered part of the “sensitive group” for exposure to pollution, and which have been studied extensively.

“Childhood cancer survivors are a bit of an overlooked population in this regard,” Ou noted, saying she believes they should be added to that list.

The study looked at 3,819 survivors of childhood and youth cancer, with records dated between 1986 and 2012. Of that group, the researchers found 185 of the individuals were hospitalized 335 times for respiratory problems — a higher rate than the average kid. That included many trips to an emergency room on days that were deemed “yellow” for particulate matter pollution by the Division of Air Quality, meaning it should be safe to breathe for most residents (even those in the “sensitive group”).

Ou called that finding “particularly striking” because it means even minimally bad air days can hurt those who have survived cancer.

Overall in Utah, there are about 15,000 survivors of childhood cancer. The rates of survival have steadily gone up in recent years, with 80 percent recovering from all forms of the disease.

Researchers worry, though, that a polluted environment will cut the gains made there.

“We don’t have all the answers yet,” said Anne Kirchhoff, a cancer researcher at the institute who led the research team and plans to look next at adult cancers and ozone pollution. “Initially, there was very little known about the effect of air pollution on cancer survivors.”

Based on the early results, Kirchhoff wants the state to rethink when it sends out public health advisories for air quality — perhaps sending them on more mild days to those more likely to be impacted. Both she and Ou plan to also speak to lawmakers and public health agencies to require that doctors give warnings about air quality to their recovering cancer patients before they are released.

Fair, the Primary Children’s Hospital physician, said he’s already started advising patients differently since the study was published late last month. At any time, Primary Children’s serves between 82% and 97% of the childhood cancer patients in the state, most 15 years old and younger.

Doctors, he believes, should tell their patients to watch the state’s air quality monitors and stay inside even on moderate days. If they experience coughing, trouble breathing and shortness of breath, they should see a health professional.

Fair follows up with his cancer patients for five or 10 years after a diagnosis. Paying attention to air quality, he said, is now part of their “survivorship care plan." His hope is that they won’t have to keep returning to hospital beds and emergency rooms once they’ve recovered.

Editor’s note • The owner and publisher of The Salt Lake Tribune is Paul Huntsman, a son of Jon Huntsman Sr., the late founder of the Huntsman Cancer Institute.