St George’s Hospital is asking patients and visitors suffering with symptoms of the norovirus to go to their GP instead of coming to the hospital.
The hospital, on Blackshaw Road, Tooting, is urging people with diarrhoea or vomiting to avoid the hospital because it can raises the risk for those patients already there.
Alison Robertson, chief nurse at St George’s Healthcare NHS Trust, said: "People with symptoms of D&V could be suffering with Norovirus, a bug which is generally unpleasant but rarely serious for otherwise healthy people.
"It can, however, become a very serious illness for patients in hospital who are already weakened by other conditions.
"Norovirus is exceptionally infectious and passes easily from one person to the next.
"This is why people suffering with D&V must not come into hospital, including those with outpatient appointments.
"Friends and relatives with symptoms of the virus are asked not visit patients on our wards until they are no longer infectious - at least 48 hours after the symptoms have stopped.
"Visitors bringing the virus into the hospital will put vulnerable patients at risk.
"With schools and local businesses gearing back up again after the festive break, the community may experience a rise in infection rates.
"This is the time to be most vigilant and avoid passing the virus to friends and family.
"The advice for healthy adults suffering with the virus is to rest, drink plenty of water and let the illness run its course."
People should speak to their GP, pharmacy or NHS Direct over the telephone if they need more guidance.