Is population mixing associated with childhood type 1 diabetes in Canterbury, New Zealand?

There is growing evidence to support a role for infections in the aetiology of childhood type 1 diabetes. However, previous studies suggest that infections can either protect against or initiate type 1 diabetes onset, depending on the timing of exposure. Population mixing has recently been employed as a proxy measure for area-level infectious exposure in childhood diabetes research. Research has found that the incidence of type 1 diabetes tends to be higher in areas with low population mixing, suggesting that children with low infectious exposure in early life have increased susceptibility to the disease. Subsequent exposure to infection could act as the final trigger to type 1 diabetes development. We assess whether an increase in population mixing over a short time period is associated with a higher incidence of type 1 diabetes. We test this hypothesis using data on childhood type 1 diabetes from the Canterbury region in New Zealand for the period 1999-2004, and population mixing change measures derived from the 1996 and 2001 censuses. We found that the incidence of type 1 diabetes was higher in areas where population mixing had increased the most. This effect was small, but remained significant after adjustment for potential confounding variables. The findings suggest that large increases in population mixing, over short time periods, could act as a trigger for type 1 diabetes development in children.