Aims: New Zealand has a higher incidence rate of giardiasis than other developed countries. This study aimed to describe the epidemiology of this disease in detail and to identify potential risk factors.
Methods: We analysed anonymous giardiasis notification (1997-2006) and hospitalisation data (1990-2006). Cases were designated as urban or rural and assigned a deprivation level based on their home address. Association between disease rates and animal density was studied using a simple linear regression model, at the territorial authority (TA) level.
Results: Over the 10-year period 1997-2006 the average annual rate of notified giardiasis was 44.1 cases per 100,000 population. The number of hospitalisations was equivalent to 1.7% of the notified cases. There were 2 reported fatalities. The annual incidence of notified cases declined over this period whereas hospitalisations remained fairly constant. Giardiasis showed little seasonality. The highest rates were among children 0-9 years old, those 30-39 years old, Europeans, and those living in low deprivation areas. Notification rates were slightly higher in rural areas. The correlation between giardiasis and farm animal density was not significant at the TA level.
Conclusions: The public health importance of giardiasis to New Zealand mainly comes from its relatively high rates in this country. The distribution of cases is consistent with largely anthroponotic (human) reservoirs, with a relatively small contribution from zoonotic sources in rural environments and a modest contribution from overseas travel. Prevention efforts could include continuing efforts to improve hand washing, nappy handling, and other hygiene measures and travel health advice relating to enteric infections.