Flies, fingers, fomites, and food. Campylobacteriosis in New Zealand--food-associated rather than food-borne.

AIMS: New Zealand has a very high rate of seasonal, sporadic campylobacteriosis compared to other OECD countries. Can the seasonality of New Zealand cases fit with an explanation of food-borne transmission (especially by chicken meat), and where does the fly-transmission hypothesis fit?
METHODS: Analysis of seasonal campylobacteriosis reports at the District Health Board level compared to regional ambient temperatures, and chicken consumption data. Literature review particularly of food-associated disease risks and transmission routes.
RESULTS: Campylobacteriosis rates in New Zealand show a national annual increase at a rate similar to chicken consumption. A drastic reduction in chicken consumption was associated with significantly reduced campylobacteriosis cases in two European countries, further strengthening the link between disease risk and chicken consumption. However, serotype analysis of the Campylobacter isolates is ambiguous regarding chicken meat itself as the major source of infection. The seasonal colonisation pattern in live chickens follows the seasonal increase in human cases. Flies are a plausible vector, associated with increasing overwintered fly foraging activity, rather than a summer increase in fly numbers.
CONCLUSION: The typically sporadic rather than outbreak nature of campylobacteriosis, the disjoint between seasonal patterns of human and chicken infection, the seasonal pattern itself, and inconclusive serotype evidence indicates against chicken meat itself as the major source of infection. However, chicken consumption is a significant risk factor.