Chief medical and dental officer Robin Whyman said RSV was now affecting adults, especially older people or those with underlying health conditions.
While most adults tend to have milder symptoms, it could cause severe illness in adults with underlying lung disease or a weakened immune system, he said.
Some elective surgeries have also been postponed this week due to the outbreak.
On Tuesday eight were postponed and on Wednesday six were postponed – these will be rescheduled.