'It could never happen here…' These are five words that sent a chill up chief medical officer Sir Liam Donaldson's spine.

About five years ago he delivered a presentation at a conference and used, very powerfully, a number of tragic stories of patients harmed or killed as a consequence of our healthcare system getting it wrong. He said he had delivered a similar presentation in a hospital and the chief executive, walking him back to his car, offered those five "reassuring" words, "it could never happen here".

But not only can it happen in any hospital, it is happening with alarming regularity. Until chief executives and other leaders recognise this, they will not be moved to do enough about changing and improving it.

Those five words were brought home starkly to me very recently. At Luton and Dunstable Hospital foundation trust we have gained a national reputation for our work to improve patient safety. This led me to take on the part time role of director of the national Patient Safety First Campaign earlier this year. While on holiday in October I received a text from my deputy at Luton telling me an E coli outbreak in our neonatal intensive care unit had made national headlines. I broke into a cold sweat and recalled those five words "it could never happen here".

Sadly, two babies had died from their extreme prematurity. Tracing the source of the infection is notoriously difficult but the fact that several babies became infected means we probably contributed to their harm. We sincerely regret this and have learned many lessons from the outbreak and how it was handled.

Reducing risk

The understanding of "human factors" in patient safety teaches us everyone is fallible. Organisations that focus on systems try to mitigate failures by building defences that reduce the risk. James Reason's "Swiss cheese" model of human error shows how there will always be a risk of holes in these defences. In each defence layer - or slice of cheese - the holes will open and close in different circumstances. On its own, a hole in one layer does not usually lead to failure. The catastrophic event occurs when the holes line up and, in Reason's words, "defences, barriers, and safeguards may be penetrated by an accident trajectory".

Reason explains: "Perhaps the most important distinguishing feature of high reliability organisations is their collective preoccupation with the possibility of failure. They expect to make errors and train their workforce to recognise and recover them. They continually rehearse familiar scenarios of failure and strive hard to imagine novel ones. Instead of isolating failures, they generalise them. Instead of making local repairs, they look for system reforms."

The outbreak at our trust is an opportunity to learn from mistakes and to model leadership behaviours that do not look for scapegoats but analyse systems and identify improvements to make. We need now to continue with our mission to make patient safety our highest priority. No NHS leader should work under the misapprehension that "it could never happen here".