A rheumatic fever screening study in Kaitaia has found six children with heart damage caused by the disease.
Cardiologists recently tested more than 700 children in the Far North, where rheumatic fever is common in the Maori community.
Northland paediatrician, Roger Tuck, says the six children confirmed with the disease will need monthly penicillin shots till they are adults, to ward off further damage.
He says about a dozen more showed signs of having had the disease, and will need close watching.
Dr Tuck says children who have had rheumatic fever generally develop significant valve disfunction as they get older which will compromise their heart function.
He says it's likely they'll need some form of treatment such as valve replacement.
Dr Tuck says none of the Far North children or their families knew they had had rheumatic fever, until the echocardiogram tests in July.
He says rheumatic fever is caused by the body's immune response to a strain of the common sore throat bacterium, streptococcus A.