Covid Scotland: Nearly 2000 patients who contracted virus in hospital have died

This represented an mortality rate of 28.2 per cent based on the 7,048 patients likely to have caught the virus in hospital.

The report by Public Health Scotland notes that the mortality rate for Covid infections caught in hospital has declined over the course of the pandemic, as a result of vaccine protection and improved medical treatments, from around 33% during wave one to 20% by wave three when Delta and latterly Omicron became the dominant variants.

Patients who test positive for Covid based on swabs taken between day eight and 14 after admission are considered "probable" hospital infections, based on the incubation period for the virus.

Positive swabs taken after day 14 are "definite" hospital infections.

Probable and definite hospital acquired Covid cases during Omicron have halved since the beginning of January

However, it is unclear how many hospital-acquired Covid cases resulted directly in patients' deaths.

Patients with probable or definite hospital-onset of Covid are more likely to be older and to have several pre-existing chronic conditions.

The report states: "Cases who are in the probable and definite category have, by the design of the case definition, been in hospital for eight days or more for another reason prior to developing Covid-19.

"This is indicative of underlying medical conditions which will also be a risk factor for mortality, and some of these patients may have died irrespective of Covid-19."

Since the first confirmed hospital Covid case on March 7 2020, the mortality rate from probable and definite hospital-acquired Covid cases has been highest among males aged 85 and over, with a total of 383 deaths out of 851 cases (45%).

That compares to 28% for female patients in the same age group.

There have been a total of 10 deaths among patients aged 25 to 44 who were infected with the virus in hospital, but none at all among younger age groups.

After adjusting for variables such as age and co-morbidities, PHS says there is "no evidence" that patients who contract Covid in hospital are more likely to die within 28 days of diagnosis compared to those who test positive on day one or two after admission, as a result of exposure in the community.

Patients infected and incubating the virus prior to admission tend to be younger.

The mortality rate for hospital-acquired Covid during the Delta and Omicron wave, at 20%, is still higher than other bacterial infections commonly associated with healthcare settings.

In 2019, nearly a fifth (18%) of people infected with Staphylococcus aureus; 13.5% of people aged 15 and over with C.diff; and 13.2% of those with E.coli infections had died within 30 days of their diagnosis.

PHS cautions that these figures are "not directly comparable" due to the differing follow up time for diagnosis to death - 28 days for Covid, compared to 30 days for the other infections - and because the latter will include both hospital and community cases.

The mortality rate for probable/definite hospital Covid cases has fallen steadily over the pandemic from around 33% to 20%

The report stresses that the protective effect of the Covid vaccines in preventing severe outcomes is "evident" over the course of the pandemic.

It states: "Inpatients who had been vaccinated with either one, two, or three doses had had lower odds of death within 28 days compared with those who had not been vaccinated.

"Protection from severe outcome by vaccination, particularly in hospital inpatients and those at risk of hospitalisation, is critical to reducing poor outcomes in patients who develop Covid-19, including nosocomial [hospital-acquired] Covid-19."

The combined number of probable and definite hospital-onset Covid cases has fluctuated over the course of the pandemic, however, from 1,355 in wave one to 4,056 during wave two - when the more transmissible Alpha variant emerged in the winter period from 2020 to 2021 - to 1,637 during wave three.

Deaths have gone from 441 in wave one, to 1,220 in wave two and 325 in wave three. 

Improvements in PPE, testing, and infection control in hospitals between wave two and three may have helped to combat the risk from the even faster-spreading Delta and Omicron variants taking off in medical wards, but PHS cautioned that future variants could still pose an increased threat to patients.

It said: "Following the dominance of the Alpha and Delta variants, the Omicron variant became the dominant strain circulating in Scotland on 17th December 2021. 

"The emergence of new variants can lead to an increased risk of Covid-19 hospital admissions as the new variant circulates in the community.

"Any future shifts in dominant strains with changes to severity of disease have implications for mortality outcome analyses and should be considered."