A young married couple in the United States have tugged heartstrings across the country after they died within days of each other.

Mr Dalton Prager, 25, and his 26-year-old wife Katlin Donovan, who went by Katie, met online in 2009 and exchanged messages about their shared battle with cystic fibrosis, which causes the lungs to be clogged with fluid.

They got married in 2011, but found themselves in need of lung transplants in 2014 when their conditions were worsened by a bacterial infection that Mr Prager passed to his wife. Mrs Prager also faced administrative difficulties securing a lung transplant.

After their operations, complications such as pneumonia and kidney failure arose. Mr Prager was hospitalised in Missouri where the couple lived, while Mrs Prager was sent home to Kentucky to receive hospice care in September.

The couple last saw each other on their fifth wedding anniversary in July, which they celebrated in hospital, as Mr Prager was too ill to travel.

Mr Prager died on Saturday (Sept 17) with his wife looking on over FaceTime. Mrs Prager died five days later.

She told CNN the day before her husband's death: "I'd rather have five years of being in love and just really completely happy than 20 years of not having anybody."

The couple had earned comparisons to the John Green novel and the 2014 film The Fault In Our Stars, about the romance between two young cancer patients.