Household crowding is being partially blamed for New Zealand having one of the highest rates of acute rheumatic fever (ARF) among children and teenagers in the developed world.
The infectious disease, which can cause chronic rheumatic heart disease through damaged heart valves, is responsible for more than 120 deaths a year.
The latest study by public health researchers at Otago University shows that household crowding is one of the key risk factors for ARF, particularly in Maori and Pacific families.
In the past few years of the study, Maori rates of ARF were 20 times, and Pacific rates 40 times, that of New Zealand European and others.
Lead researcher Dr Richard Jaine and Associate Professor Michael Baker looked at 1249 cases of people hospitalised with ARF between 1996 and 2005, and related them to census data and household crowding.
"We found a clear and positive association between household crowding as a risk factor for ARF incidence, and this effect persisted after controlling for age, ethnicity, household income and density of children in the neighbourhood," Dr Jaine said.
The study shows the ARF rate for areas with the most crowded households, where there are not enough bedrooms to sufficiently cater for the house occupants, are close to 90 per cent higher than for areas with the least crowded households, he said.
ARF is not strongly related to low income, as low income Europeans and others have much lower ARF rates than Maori and Pacific households.
"It's of serious concern that in other developed countries acute rheumatic fever is often not even recorded in health statistics because it's almost non-existent, yet in New Zealand rates have remained persistently high over the last 10 to 20 years in Maori and Pacific families, and continue to rise.
"This research is further evidence of the need for much more effective public health interventions in high risk areas regarding sore throats and ARF," Dr Jaine said.
"New Zealand research has already shown that we should be able to reduce ARF by as much as 60 per cent through well-resourced school-based `strep' throat treatment programmes. This would avoid costly medical treatment, heart valve replacements and monthly penicillin injections in teenage years and later life."
Dr Jaine said the latest research also indicated the importance of appropriate social housing at affordable rents for low income families, avoiding high-risk families `doubling-up' in overcrowded homes.
The study has recently been published in The Paediatric Infectious Diseases Journal, and has been carried out within the He Kainga Oranga/Housing and Health Research Programme, supported by the Health Research Council of New Zealand.