A tale of two parasites: the comparative epidemiology of cryptosporidiosis and giardiasis.

New Zealand has a higher reported incidence of cryptosporidiosis and giardiasis than most other developed countries. This study aimed to describe and compare the epidemiology of these infections in New Zealand, to better understand their impact on public health and to gain insight into their probable modes of transmission. We analysed cryptosporidiosis and giardiasis notification data for a 10-year period (1997-2006). Highest rates for both diseases were in Europeans, children aged 0-5 years, and those living in low-deprivation areas. Cryptosporidiosis distribution was consistent with mainly farm animal (zoonotic) reservoirs. There was a dose-response relationship with increasing grades of rurality, marked spring seasonality, and positive correlation with farm animal density. Giardiasis distribution was consistent with predominantly human (anthroponotic) reservoirs, with an important contribution from overseas travel. Further research should focus on methods to reduce transmission of Cryptosporidium in rural areas and on reducing anthroponotic transmission of Giardia.