Disease surveillance in rural communities is compromised by address geocoding uncertainty: a case study of campylobacteriosis

This study illustrates the impact of address geocoding uncertainty on rural estimates of reportable disease incidence using campylobacteriosis as an example. After all cases of campylobacteriosis notified from 1993 to 1997 had been geocoded, the minimum and maximum disease notification rates were calculated for rural and urban areas of New Zealand. The estimated maximum rural rates were four times higher than estimated minimum rural rates, whereas estimated minimum and maximum urban rates varied minimally. The impact of address geocoding on the estimation of disease notification rates across Public Health Service Regions showed considerable variation. The relative proportions of ungeocoded notifications to rural notifications ranged from 1.3:1 to 10.2:1, reflecting the range of uncertainty in estimated rural rates of campylobacteriosis. Unless the reliability of captured rural address data is improved significantly, disease surveillance systems will underestimate rural rates of disease and limit small area analyses