North Island hospitals have been swamped with cases of infants struggling to breathe and there are fears the virus will spread further and faster with school holiday travel.
DHB chief medical officer Dr Graham Roper says the confirmed West Coast cases are among an increasing number of patients showing up with respiratory troubles.
"We're unable to confirm whether the other presentations are all due to RSV specifically as viral testing is not conducted on every patient with a respiratory illness … treatment is provided on a case-by-case basis, which may include hospitalisation."
Medical officer of health Dr Ramon Pink says RSV is "incredibly infectious" and can easily pass from person to person through coughing and sneezing.
"For that reason we're asking parents and caregivers not to visit anyone in hospital if they are unwell themselves -- fewer people means less risk to the baby or patient."
Hospital visitors should wear masks if they could not physically distance themselves from strangers, or if they were visiting someone vulnerable, Dr Pink said.
RSV symptoms include a runny nose, reduced appetite, coughing, sneezing, fever and wheezing or noisy breathing.
"It can cause more serious illness such as bronchiolitis, the narrowing of airways in infants and pneumonia -- in which case they will need hospital care."
Parents and caregivers should seek urgent medical advice if their baby or infant had symptoms and was under three months old, Dr Pink said.
West Coast residents should call their GP during normal hours, and Healthline on 0800 611 116 after hours.