A paper presented to the government advisory board found that as many as 40 per cent of hospital patients with Covid caught it after they were admitted.
And this spread between patients and hospital staff meant that the first phase of the epidemic was ‘prolonged, potentially by several weeks’, they said.
The spread of the virus on wards has been a problem for the
Although staff must wear protective equipment at all times and Covid and non-Covid patients are segregated, the virus can still spread from people who don’t have any symptoms or who get false negative test results.
The SAGE paper, published today, suggested that as many as 36,152 of around 90,000 people who were diagnosed with the virus in hospital between February and July 2020 had caught it in hospital.
This included people who became ill while an inpatient for another condition, or who developed Covid-19 shortly after being discharged and then ended up back in hospital. Some of the cases were only suspected, while others were confirmed by process of elimination.
Preventing the spread inside hospitals, the researchers said, could have had a ‘substantial’ impact on deaths because the patients were often old or frail.
It is too soon to know whether in-hospital transmission was reduced in the second wave, with 24,000 people still on wards with Covid-19 across the UK. The most recent NHS data for England suggests
The study, published by SAGE today, found that at times more than half of Covid patients in hospital appeared to have caught the virus after being admitted. The red bars represent the proportion of people who definitely caught the virus before they came in. The purple and blue represent varying levels of certainty about where people got infected, with the lightest blue representing people who were diagnosed more than two weeks after they got sent to hospital, meaning they definitely didn’t have it when they went in
The paper showed that even people who didn’t obviously catch the virus in hospital may have done so if they developed symptoms shortly after being admitted and then ended up back in hospital with Covid-19
The paper estimated that at least 8.8 per cent of Covid-19 hospital cases in England over the first wave of the pandemic may have been what are known as nosocomial, or hospital-acquired, infections.
The 8.8 per cent figure was for people who tested positive 15 or more days after being admitted, who were certain to have caught the virus in hospital.
But as the criteria were broadened, the proportion of people whose illness could be traced back to a hospital stay got significantly higher.
Including people testing positive after eight days or three days if they had been recently discharged from hospital, it doubled to 18.3 per cent; one in five. Those people were considered highly likely cases of in-hospital infection.
When the three-to-seven days group with no recent hospital stay was included it was 25.9 per cent, and when all of the above were combined with people who had recently been to hospital and tested positive on day two of their second stay, it rose to 40.5 per cent.
The latter groups were the least likely to have caught the virus in hospital but the risk was still high enough for them to be counted as possibles.
Medical workers travelling in and out of the hospital every day unavoidably raises the risk of this transmission, and the risk of it spilling out into the community, although this wasn’t studied in the paper.
The paper said that while the proportion of the total Covid-19 cases linked to hospital transmission was large, it was relatively small in terms of the entire outbreak.
Because so many of them were likely to have been vulnerable people, however – and hospital patients have a significantly higher death rate than the general population – the in-hospital spread may have killed thousands of extra people.
The undated document said: ‘A simple calculation assuming five per cent of infections are hospitalised and of these hospital cases, if 25 per cent are due to nosocomial infection, the complete prevention of nosocomial transmission would have led to approximately one per cent impact on the number of infections in the English epidemic overall.
‘However, since hospitalised patients tend to be old and/or frail, the impact in terms of morbidity and mortality would nonetheless be expected to be substantial.’
The paper also warned that the risk of in-hospital transmission was that it would spill out into the community, and that this was making the outbreak go on for longer.
It added: ‘An exploration… shows little impact of nosocomial transmission initially, but in the last quarter of the first wave the impact of nosocomial transmission may have been to prolong the epidemic, potentially by several weeks.’
The explanation for this was that people were being discharged from the hospital while still infectious, passing it on to others.
Staff would also inevitably be more likely to catch the virus if more patients were carrying it, and they would then take it home to their families.
The study said: ‘A number of the nosocomially infected patients will be discharged and lead to onward community transmission.
‘Modelling this onward transmission crudely, with a time-varying R, up to the fourth generation of transmission, gives 50,550 onward infections.
‘A proportion of these infections will progress to disease and subsequently be hospitalised.’
It added that when taking into account missed hospital-acquired infections – those whose symptoms started after they were discharged or before the time cut-off – as many as 31,000 went uncounted in England over the first wave.
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