Norovirus has forced 10 wards to close at Southampton General Hospital, while there has also been an outbreak of the vomiting bug at hospitals in Leicester.
The hospitals are the first in the UK to report cases of the virus this winter. The bug spread across the country last winter infecting over 1 million people - more than ever before.
Southampton General Hospital has told families not to visit and the affected wards are closed to new patients in order to prevent the sickness from spreading.
Visitor restrictions are in place across the Southampton General, Princess Anne Hospital and Countess Moutbatten House, all of which are run by University Hospital Southampton NHS Foundation Trust, in an attempt to contain the virus.
In Leicester, Leicester Royal Infirmary, Glenfield Hospital and Leicester General Hospital have all hit by the virus, with admission restrictions being placed on some wards.
Those arriving for medical attention who are suffering from diarrhoea or vomiting should notify staff at the hospitals immediately so they can be treated separately.