The public is being misled by scare stories about sepsis, say experts, warning that hype and misunderstandings about the so-called “hidden killer” have generated “an unhealthy climate of fear and retribution” in the UK and the US.

The health secretary, Matt Hancock, has contributed to the mythology, they say in a letter to a leading medical journal. In March, Hancock tweeted: “Sepsis kills over 52,000 every year – each death a preventable tragedy.” The figure was an estimate from a charity campaigning for awareness on sepsis.

This is wrong, says Prof Mervyn Singer and colleagues from the Bloomsbury Institute of Intensive Care Medicine at University College London – adding that the numbers are not that high and sepsis is not always preventable. “Many other non-contextualised or fictitious claims regularly fill media pages and airwaves,” they say in their letter to the Lancet, calling for a rethink of the approach to sepsis risk.

The truth, they say, is that sepsis kills a very small proportion of patients – and those who die are overwhelmingly very elderly or frail. Their deaths are not always preventable because their chances of surviving their illness were not high to begin with. And the drive to ensure all patients suspected of sepsis get antibiotics within an hour is unhelpful and leading to unjust criticism of doctors and litigation against hospitals, they say.

The responses to Hancock’s tweet from doctors were swift and robust, calling on the health secretary to correct his statement. “It gives the message that 52,000 are needlessly dying because of medical neglect and the truth is far from that,” said Dr Manu Shankar-Hari, an immunobiologist and another author of the letter.

Sepsis is an extreme reaction of the body to infection. The immune system goes into overdrive in an attempt to fight off the bacterial infection and shuts down the body’s organs.

Most patients with substantial organ dysfunction are admitted to intensive care, the letter says. Those who die outside of intensive care, and many who die inside it, are older and frail and have other illnesses. More than three-quarters of those who die of or with sepsis are older than 75. In many ways, they suggest, sepsis may have taken over from pneumonia as “the old man’s friend” – a short illness leading to a not-unexpected death.

Sepsis cases are not accurately counted and the numbers have risen in response to NHS financial incentives introduced in April 2017 for hospitals to record diagnoses of sepsis. But up to 40% of patients diagnosed are later found not to have it at all. A study of 521 patients diagnosed with sepsis in Welsh hospitals, 136 of whom died, found that only 40 of the deaths were directly or possibly linked to sepsis and three-quarters of those were very frail.

“We are not defending malpractice,” said Singer. “There are some barn-door cases where things should have been done.” But they are concerned that doctors are under pressure to give antibiotics they do not think are appropriate, potentially fuelling the antibiotic resistance problem. Some doctors have been reported when they have taken a considered decision not to prescribe them.

“We are being encouraged to throw antibiotics at the problem,” said Shankar-Hari. “But the data is not strong.”

Sepsis is particularly emotive when children die, they say, which happens to about 150 a year – not 4,000 a year, as previously reported.

“It is crucial to expose the fictions surrounding sepsis, to provide a proper perspective for better understanding of the condition and to create realistic expectations about outcomes,” they write.

“The rare cases of severe infection (eg, in patients with shock) should be promptly recognised and treated, as with any emergency condition, and unnecessary delay should be avoided in less sick patients. Patients with sepsis might die despite the best care, yet the large majority who are salvageable do survive.”

A Department of Health and Social Care spokesperson said: “Sepsis can be life-threatening and it is absolutely right the NHS has focused on improving awareness, diagnosis and treatment of this syndrome. While the number of people identified as at risk of sepsis has increased, mortality rates are falling.”