Parents living in Sandwell are being urged to protect their babies against whooping cough after four cases were confirmed in a fortnight.
All children should be fully immunised, although two of the reported cases affected babies aged between two and three months - too young to have completed the immunisation programme.
Public health staff across Sandwell's three primary care trusts are now working with local Health Protection Agency consultants to manage the situation.
Parents of any baby or child born before 1996 are recommended to check with their GP or health visitor that their children are fully protected.
Dr John Middleton, Sandwell PCTs' director of public health, said: "Children over the age of nine and young adults who did not routinely receive a full course of vaccines should take the opportunity to check that they are fully protected.
"Immunisation is a safe and effective way of protecting against serious disease, including whooping cough."
It is important to check the immunisation status of older children as it is possible that babies could be infected by older children.
Symptoms can appear to be similar to those of a cold, and although a violent cough can last up to three months it may not have the characteristic "whoop" - particularly in babies.