Two people suffering from diarrhoea and vomiting thought to be the Norovirus stomach bug have died in hospital.
The deaths were caused by underlying medical conditions, NHS Greater Glasgow and Clyde said.
A spokesman for the health board said: "Our thoughts and sympathies are with the patients' families at this difficult time."
Six wards at Royal Alexandra Hospital in Paisley are not admitting new patients because of an increase in the number of patients with Norovirus symptoms.
Twenty six patients are showing symptoms of the virus but none of those affected are giving cause for concern. Infection control measures are in place.
Dr Teresa Inkster, consultant microbiologist at NHS Greater Glasgow and Clyde, said: "Norovirus is particularly prevalent at this time of year and it's not unusual to see this type of virus in the community and also in healthcare settings.
"We are urging any visitors who have experienced any symptoms of diarrhoea or vomiting within the last forty-eight hours not to visit the hospital.
"We also request that visitors are restricted to close family and friends wherever possible due to the current situation, and that visitors follow all the infection control protocols we have put in place.
"It is important to remember that this virus is extremely common in the wider community and, therefore, we would like to remind hospital visitors of the importance of hand hygiene when entering and leaving hospital premises."
Meanwhile, NHS Highland has shut two hospital wards over concerns about staff and patients catching the bug.
Ten patients and 10 staff have fallen ill at Raigmore hospital in Inverness, where one ward has been closed to new admissions.
At Caithness general hospital in Wick, one ward has also been closed to new patients after five patients and seven staff were affected.
Norovirus is thought to be the possible cause of the sickness.
For more information on norovirus, visit the STV Health Centre, brought to you by NHS inform.
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