A two-year-old girl died as a result of neglect after the gross failure of doctors to diagnose sepsis, a coroner has ruled.

Marcie Tadman was treated for pneumonia at the Royal United hospital (RUH) in Bath and was seen by seven doctors. She died after a cardiac arrest.

During the inquest Marcie’s father, James Tadman, said: “They had been telling me all day she was going to be fine. They couldn’t explain why there had been so little concern and why we had received so much reassurance and then she had died.”

The senior coroner for the Avon area, Maria Voisin, listed a range of failings by the hospital and recorded a conclusion that Marcie died from natural causes contributed to by neglect.

She said: “I consider that putting these basic failures together led to the gross failure to provide or perform any effective medical treatment [and] the gross failures to follow proper or routine procedures and protocols including standard monitoring.

“There was a serious deterioration in Marcie’s condition, and staff caring for her should have realised the need for action in all the circumstances. I find that the gross failure has caused or significantly contributed to Marcie’s death.”

James Tadman said in a statement that the hospital “let my little girl down with such tragic consequences” and he hoped lessons had been learned. His wife died of cancer months before Marcie’s death.

An expert witness, Dr Nelly Ninis, told the inquest that systemic failures on the children’s ward led to Marcie’s death. She said Marcie would not have died had staff followed their own guidelines and those of the National Institute for Health and Care Excellence (Nice) and transferred her to a paediatric intensive care unit.

“There was such a systemic failure here to manage a child with a serious illness. It was so remarkable – the lack of attention to detail – one does have to wonder if this is a common feature in this unit,” Ninis said.

She said the sepsis should have been recognised by doctors in the emergency department. “She should have been sent to Bristol within a few hours and had much more prompt antibiotics and resuscitation. I think if this process had been in place she would have had a stormy time in the intensive care unit, but I think she would have survived.”

Tadman took his daughter to A&E at the RUH early on 4 December 2017 because she had a cough, high temperature and had been vomiting. Doctors suspected pneumonia and admitted her to the children’s ward.

Tadman told the inquest at Avon coroner’s court: “A nurse told me she was suffering from a simple chest infection, possible pneumonia, and antibiotics would be given and she would be right as rain.”

That night he fell asleep next to his daughter’s bed, and woke at 2am on 5 December to find she had been sick again. “She looked worse and very unwell,” he said. “No one else seemed concerned.”

He told Marcie that everything would be all right. “She looked at me and said ‘OK Daddy,’” said Tadman. But as he held her hand she went limp. “I looked at the nurse and she had a look of horror on her face and shouted ‘crash’. I couldn’t believe this was happening.”

Marcie died shortly before 6am. A postmortem examination found she died from a group-A streptococcus infection with secondary pneumonia.

Dr Fran Hofmann, a registrar, told the inquest she had thought about sepsis but did not share her concerns with others. She left the hospital at 5pm on 4 December believing Marcie would be reviewed immediately by the evening team. But that did not happen. “I have had a lot of difficulty understanding what fell down from the 5pm handover,” she said.

Hoffman said practices had been changed but the current way of dealing with suspected cases of sepsis was not “ingrained” at the time.

Dr Ron Daniels, the chief executive of the UK Sepsis Trust, said: “Marcie’s tragic case shows that if healthcare professionals do not ‘think sepsis’ when a patient presents with signs of severe infection, the consequences can be devastating. Not every death from sepsis is preventable but if healthcare professionals listen to families’ instincts about their loved ones and perform a structured set of clinical observations, those deaths which are preventable can be avoided.

“This is why we fully support the new hospital guidelines announced [on Monday] by NHS England to ensure that doctors are following protocol. We know that it saves thousands of lives every year.”

Tadman’s statement said: “We have lost a very beautiful, caring little girl whose smile would light up any room and melt any heart. We put our trust in the Royal United hospital, assuming that our little girl would be getting the very best care, but tragically that was not the case.

“Sepsis is not a new illness and accounts for 46,000 deaths every year. Despite that the hospital did not recognise any of Marcie’s symptoms or listen to any of our concerns until it was too late. We can only hope that lessons have been learned and that every child that receives treatment at the RUH in the future will be better protected.”

Dr Bernie Marden, the medical director at Royal United Hospitals Bath NHS foundation trust, apologised to Marcie’s family. “I want to say sorry,” he said. “As an organisation we recognise the responsibilities we hold and we feel we let Marcie down and we let you down as a family.”

He added: “This should never have happened. We owe it to Marcie’s family to demonstrate that we have learned from their devastating loss and that we are doing everything we can to make sure a tragedy like this does not happen again.

“We have carried out a comprehensive investigation into the circumstances in the lead-up to Marcie’s death. The findings and the improvements we have made and will continue to make have been shared with her family and the coroner.”