Northland Health has issued a public health alert to GPs around the region, after the discovery of new cases of rheumatic fever.
The disease can cause heart damage and still afflicts children in deprived parts of New Zealand.
New acute cases include two children in the same primary school class in Kaikohe.
Northland Health plans to throat-swab all their classmates and those found to have Strep A infections will receive antibiotics.
A echo-screening programme in Kaitaia last year revealed that one child in 100 had undiagnosed heart damage caused by untreated rheumatic fever.
The Child Poverty Action Group in Northland says rheumatic fever is regarded as a third world illness - and it's shameful that it still exists in New Zealand.