While prevalence of the disease among Pakeha declined dramatically in the last few decades to be almost non-existent, rates for Maori and Pacific children have remained high.
Study findings show the mean annual number of cases between 2002 and 2006 in Northland was 9.2. This jumped to 13.6 per year between 2007 and 2011 - a concerning trend, study authors said.
"Rheumatic fever rates are very high for school aged Maori in Northland, with an increasing upward trend in cases over 2002 - 2011," researcher Dr Roger Tuck, Northland District Health Board paediatrician, said.
A breakdown of Northland's rheumatic fever cases analysed in the study found 95 per cent were Maori.
The disease strike rate was 7.7 per 100,000 people for Maori, compared to 0.6 per 100,000 people for non-Maori.
This worsened when only Maori children, aged five to 14 years, were considered - spiking to 78 cases per 100,000 Northland Maori children.
The rate was similar to those found in developing countries and nearly double those seen among Maori children in Auckland between 1993 and 1999 (41.2), and Waikato between 1998 and 2004 (39.6).
The Tairawhiti region, which covers the Gisborne area and has a similar population proportion of Maori to Northland, also has high rheumatic fever rates.
For children aged five to 14 years it was 59 per 100,000. The overall rate was 7.6 cases per 100,000 people.
About 150,000 people were estimated to be living in Northland, of which 30 per cent were Maori, the study said.
Northland Maori were significantly younger than non-Maori and had high levels of socio-economic deprivation and unemployment compared with the New Zealand population.
One-parent families were also more common, research used in the Medical Journal study found.
Dr Tuck said: "It is clear that the upstream, issues of poverty, poor housing and overcrowding for our children still urgently need to be addressed."
His concerns were echoed by Dr Nikki Tuner, a member of the Children's Commissioner's child poverty expert advisory group.
"Rheumatic fever is particularly severe for Pacifica and Maori children, but much, much worse if they come from poverty.
"What we have to do to tackle this is face New Zealand's issues around child poverty."
Those affected by Rheumatic fever were prone to sore joints and severe fatigue.
"You can be sick for weeks, months and very incapacitated - you could miss a lot of schooling.
"A lot of children then go on and have chronic heart disease for the rest of their lives," said Dr Tuner.
Many children will also undergo major heart surgery as adults and have a reduced quality of life, she said.
Around 270,000 New Zealand children live in poverty, according to the Children's Commissioner's statistics.
Addressing this inequality was the first step in tackling poverty-related diseases, like Rheumatic fever, Dr Turner said.
"Poverty is not straight income, but we know that income makes a big difference."
Recurrent illnesses, problematic family situations and high levels of stress were commonly associated with lack of income, she said.
Smoking, drug and alcohol problems and mental-health issues were also significant factors in tight financial situations.
Extending free healthcare services to all children aged under 18 could improve New Zealand's rheumatic fever rates, Dr Turner said.
Tackling sub-standard housing and wider income-level problems among New Zealand's poorest was also important.
Northland's Rheumatic Fever rates:
• Maori: 7.7 per 100,000 people effected
• Non-Maori: 0.6 per 100,000
• Maori children, aged five to 14 years: 78 per 100,000
Rheumatic fever around New Zealand:
• Between 1993 and 1999, 41.2 per 100,000 Auckland Maori children were affected
• Between 1998 and 2004, 39.6 per 100,000 Waikato Maori children were affected
Source: NZMA, The epidemiology of acute rheumatic fever in Northland.
