A baby with a serious heart condition has died after she received an infection from mould in a Seattle hospital's operating room, her mother says.

Elizabeth Hutt was born with a heart condition that she battled for the entirety of her six-month-long life. The young child underwent three open heart surgeries, and after the third one is when it's believed she contracted an Aspergillus mould infection in the hospital's operating room.

Her mother, Katha Hutt, revealed in a Facebook post her daughter died early Wednesday morning at Seattle Children's Hospital.

"Elizabeth Vera Hutt gained her wings on her 175th day of life at 4:40 am. Late last night, Beth told us she was ready," Mrs. Hutt wrote.

"I cannot begin to express the gratitude we have for the team that worked through the night to make sure Beth's transition was as painless and smooth as possible. We will post when we've had the chance to make plans for celebrating our brave, courageous, beautiful warrior."

World's smallest baby leaves hospital at five months Show all 5 1 /5 World's smallest baby leaves hospital at five months World's smallest baby leaves hospital at five months The world's smallest baby has left hospital five months after her birth AFP/Getty World's smallest baby leaves hospital at five months Baby Saybie weighed just 245g, when she was born AFP/Getty World's smallest baby leaves hospital at five months Saybie was born after just 23 weeks of gestation AFP/Getty World's smallest baby leaves hospital at five months Doctors told her father that he would have just one hour with his child before she died, the hour became two, then a day, a week, now months AFP/Getty World's smallest baby leaves hospital at five months Saybie was born in December 2018 at the Sharp Mary Birch Hospital for Women & Newborns in San Diego, California AFP/Getty

The mould in the hospital's operating rooms was first detected in November, around the same time as the child's third surgery.

Ms Hutt created a Facebook page titled Beth's HLHS Journey to keep people updated on her daughter's condition throughout her surgeries. She revealed in January her daughter was battling an infection that stumped her doctors.

It was later determined the infection was contracted from the mould discovered in three of the 14 operating rooms at the hospital in November. The mould came from the hospital's air-handling units in the operating rooms, and 14 patients have developed infections from the mould since 2001, the hospital revealed. Seven of those 14 children have since died from their infections.

"I'm always going to wonder if there were different interventions that could've taken place, had the Aspergillus not been there," Ms Hutt said.

Aspergillus is a common mould typically present in the air that people breathe. It normally does not cause one to get sick, but it can be harmful to people who lack strong immune systems or those who are surgical patients.

Ms Hutt and her husband, Micah Hutt, told WBTV they knew about the hospital's Aspergillus problems in 2018, but they still picked the location for their daughter due to the quality of doctors and medical staff at the facility.

At the time, the parents thought the mould problem was solved.

They joined a class action suit against Seattle Children's Hospital in January, which alleges facility managers knew about the mould since 2005 and failed to fix the problem.

The hospital currently has 11 of its 14 operating rooms shut down, as new HEPA filtration units are installed. The other three operating rooms received the new air units and are open for use.