Johnson, Ellie

Identifying outbreaks of campylobacteriosis: A case study in Hawke’s Bay

Ellie Johnson and Jonathan Marshall

Institute of Fundamental Sciences, Massey University, Palmerston North

In August 2016, a large water-borne outbreak of campylobacteriosis occurred in Havelock North in the Hawke’s Bay, resulting in an estimated 5,000 cases of disease from a population of 15,000. In such large outbreaks, identifying the common exposure is possible as a wealth of epidemiological information are available from the large number of cases and, with knowledge of the exposure, future risk may be reduced or eliminated through targetted mitigation. However, most cases of food and water-borne campylobacteriosis in New Zealand and world wide are due to isolated events where only a small number of people get sick. In such situations, identifying a common exposure to link cases can be difficult due to sparse epidemiological information. One technique is to model the underlying spatial \(U_i\) and temporal \(R_t\) trends in notification rate \(\lambda_{it}\), with a spatio-temporal field of outbreak indicators \(X_{R[i]t}\) across regions \(R[i]\) over and above these trends: \[ \begin{aligned} Y_{it} &\sim \mathsf{Poisson}({n_{it}\lambda_{it}})\\ \lambda_{it} &= R_t + U_i + \beta_{R[i]} X_{R[i]t} \end{aligned} \] We apply this model to Hawke’s Bay campylobacteriosis notifications from 1997 through 2016, and show that many of the potential outbreaks prior to the large outbreak in August 2016 also occurred in the town of Havelock North.

This is a lightning talk.