Hawke's Bay Hospital is busy with increased admissions of people with respiratory illnesses, and is expecting another surge in coming weeks.
Chief medical and dental officer Dr John Gommans said that with the cold, winter weather people were spending more time indoors together so infections spread more easily to children and older people, who were more susceptible to illnesses such as asthma, pneumonia and bronchitis.
"A lot of it is just ordinary viruses because it's a bit colder, and people who are fit are spreading it without realising.
"We really want to encourage people if they are feeling sick to get to their family doctor or medical centre before their symptoms get worse.
"Early treatment, particularly in children and older people, can help prevent the need for hospital care."