A public inquiry heard health watchdogs failed to report concerns to inspectors about unexplained and unexpected deaths in the neonatal unit at the Countess of Chester Hospital.

A team from the Care Quality Commission (CQC) carried out a routine inspection of the hospital on a four-day visit in February 2016, followed by unannounced visits in the weeks that followed.

During the initial investigation, pediatric serial killer nurse Lucy Letby attempted to kill the girl named Child K by removing her breathing tube in the early morning hours of February 17.

Earlier that month, an external “thematic” review into 10 deaths at the unit in 2015 and January 2016 noted that “some of the infants had deteriorated suddenly and unexpectedly and there was no clear cause for deterioration/death identified”.

It was also found that six babies were arrested between midnight and 4am, but there was no common theme across all the cases examined, the Thirlwall Inquiry into the events surrounding Letby’s crimes heard.

On Thursday CQC inspector Helen Cain said she was unaware of the inspection at the time of the visit.

Asked what her response would have been if she had received the report, Ms Cain said: “Specific questions would have been asked about what action was taken following the identification of a perceived or increased rate of neonatal deaths.”

Inquiry consultant Craig Carr said: “You’re not focusing on issues around neonatal deaths, you’re not asking direct questions in relation to those areas because you were unaware of the concerns that we now know were there?”

Ms Cain said: “No.”

Mr Carr said: “Were the incidents of unexplained and unexpected deaths never discussed?

“No,” said Mrs. Cain.

Mr Carr said: “The CQC inspection did not identify concerns that we knew existed in the neonatal unit. What is your explanation for why some of these concerns were not identified?”

Ms Cain said: “I think part of it is the data. There is always a lag in history and data sources, so I think this should be taken into account. “And I think with on-site investigation you can ask a lot of open questions, a lot of general questions, but you rely too much on people’s answers.”

He said none of those interviewed, including counselors and nursing managers, expressed concerns about rising neonatal deaths or unexplained and unexpected deaths.

Letby, 34, from Hereford, is serving 15 life sentences after being found guilty at Manchester Crown Court of murdering seven babies and attempting to murder seven more between June 2015 and June 2016, as well as making two attempts on one of his victims.

The investigation at Liverpool City Hall is expected to continue until early 2025, with findings published in the late autumn of that year.