Disease incidence in Southern California

Huanglongbing, if left unchecked, will always spread in an exponential fashion. DATOC was tasked with determining if the rate of HLB detection in Southern California is also increasing exponentially, with the goal of informing the CPDPP as they determine at what point current regulatory activities may become impractical due to an overwhelming infection rate. 
Project Timeline

August, 2018

A Science Task Force convened, with the goal of advising the CPDPP Executive Committee on the effectiveness of certain program activities and to provide input for future planning. One of the task force’s key findings was that the rate of increase in detection of huanglongbing (HLB) should be carefully monitored, to determine at what point current regulatory activities may become impractical due to an overwhelming infection rate. DATOC was then asked to determine if the growth of disease incidence was following an exponential pattern. 

October, 2018

DATOC reported on the project progress thus far. Rather than showing a strict exponential pattern of growth, the increase in the rate of disease detection could also be explained by a "broken stick" model, in which two different linear rates of growth are seen, with a sharp change in directionality between the two. Although the data are preliminary at this time, the recommendation is that the CPDPP proceed as if exponential growth in disease detection is occurring in Southern California. 

Moving forward, DATOC will pursue incorporating sampling intensity or other confounding factors into the model. 

March, 2019

DATOC has finalized the project report.  As preliminary work showed, the rate of disease detection is best explained by a "broken stick" model, in which a sharp increase in the rate of detection occurs about halfway through 2017. It is unknown, however, if this is limited by program capacity. DATOC recommends that the CPDPP discuss utilization of the APHIS/Cambridge model to run periodic predictions of the California situation.

Open the report:

A note about the report: DATOC received inaccurate data from the CDFA. Quadrant sampling is listed in the report as starting in December, 2017. It actually started in August, 2017.

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DATOC is sponsored by the Citrus Research Board and the California Citrus Pest and Disease Prevention Program.