Two adults are now in the Hawke's Bay Hospital intensive care unit, alongside three children, after being struck down by respiratory syncytial virus.
The outbreak of RSV has been spreading throughout New Zealand since the transtasman border opened and clogging hospitals for about two weeks.
As of Thursday afternoon, there were 25 children in the Hawke's Bay Hospital children's ward, the majority with RSV or suspected RSV.
On Tuesday, Hawke's Bay DHB said RSV cases were continuing in children and increasing in adults.
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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.
Some minor day surgeries were postponed on Thursday, but this was due to staff sickness, not hospital capacity.
Parents are urged to keep children home if they are sick and home from childcare if they have younger or baby siblings.