A young US married couple who bonded through their shared struggles with cystic fibrosis have died within days of each other.

Katie Prager, 26, died in Kentucky on Thursday, five days after the death of her husband, Dalton Prager, 25.

Katie died in bed on Thursday morning, her mother wrote on Facebook.

“I know Dalton was waiting with open arms, as well as both her grandmothers and a host of family and friends that have gone before her,” she wrote.

The couple married in 2011 after falling in love on Facebook.

Doctors had advised against meeting in person, due to the likelihood that Dalton would pass a highly-infectious disease to Katie.

The couple had been forced to live in separate states in recent years and were last together for their fifth anniversary in July. Katie had lived in Kentucky, while Dalton was living in Missouri.

Cystic fibrosis clogs the lungs with mucus making it difficult for patients to breath. The median survival age is 40-years-old.

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They had each received lung transplants, which failed.

Dalton had tried desperately but was unable to travel to Kentucky to see Katie one last time before his death.

“He has tried so many times and he has tried so hard. Unfortunately his body is not agreeing with what he wants to do,” his mother Renee Prager told the St Louis Post-Dispatch.

The couple raised money for their treatment, and wrote extensively about their difficult experiences.

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Lamenting how he and his wife were treated by health insurance companies,Dalton wrote: “They are turning my wife into a number, a statistic, a dollar sign. I cannot lose her! This can’t be the end of our love story!

“We are both ready to continue fighting but at this point we are running out of options and need your help. Please help me save my wife Katie!

“We knew her time was short and she was able to do a few things that she wanted,” Katie’s mother Debbie wrote.

“The days to follow will not be easy but I find comfort in knowing that my girl lived, she really lived.”

The couple were compared to the one in the book and film The Fault In Our Stars, that focuses on a young couple battling cancer.