THE number of patients contracting Covid in hospital more than doubled at the end of last year following a surge in cases driven by the highly transmissible Omicron variant.

A total of 283 patients in the week ending January 2 were diagnosed with infections which were ‘probably’ or ‘definitely’ the result of catching the virus following admission, up from 112 the week before and 36 at the beginning of December.

Hospital onset cases are gauged based on when a patient’s first positive Covid swab is collected.

A patient is considered to have ‘probably’ become infected in hospital if they test positive for the first time on a PCR test taken on days eight to 14 following admission, or ‘definitely’ if the they test positive from day 15 onwards.

Hospital-onset cases in Scotland peaked at around 350 a week in mid-January last year.

The Herald: Hospital onset cases based on timing of positive testHospital onset cases based on timing of positive test

Patients can be incubating the virus on admission and test negative, or it can be brought into hospitals by staff and visitors.

However, once any patient tests positive for Covid - even if they have no symptoms and are being treated for other conditions - they must be isolated from non-Covid patients in separate ‘red’ zones, causing logistical problems for the NHS.

Professor David Livermore, a medical microbiologist at the University of East Anglia, said the high transmission in hospitals is down to Omicron’s sheer transmissibility.

He said: “Even if you assiduously screen every admission you’ll miss those who only caught the virus on the previous day or two and, a day or two later, they’ll have sufficient virus to start infecting others.

“And, someone boosted 10 weeks ago will already have diminishing immunity and be more likely to catch it on the ward.”

He said it was important - but difficult to determine - how much of the hospital spread of the virus is down to patient-to-patient or staff-to-patient transmission.

NHS staff who have tested positive for Covid can return to work in frontline care from day seven in Scotland if they are testing negative using a lateral flow device.

A separate analysis by Public Health Scotland - which excludes hospital-onset cases - also found that 64 per cent of the ‘Covid’ patients in hospital were admitted ‘because of’ the virus, against 68% when Delta was dominant.

The remainder had tested positive coincidentally.