Andres PerezAssociate Professor, CVM, UMNaperez@umn.edu

Spatial epidemiology of PED

2014 Allen D. Leman Swine ConferencePre-conference workshop

September 13, 2014St. Paul RiverCentre, St. Paul, Minnesota

Introduction

Coauthors

Julio Alvarez (DVM, PhD) Research Associate, CVM, U of MN

Dane Goede (DVM) Research Assistant, CVM, U of MN

Bob Morrison (DVM, PhD)Professor, CVM, U of MN

Objective and methods

• To assess the spatial dynamics of PED spread in two case-studies (NC and IA)

• Techniques used– Cuzick-Edwards’ test

• Do cases tend to neighbor other cases?

– Knox / Mantel test• Do cases tend to cluster within critical times and distances?

– Directional test• Do cases spread on a given direction?

– Scan statistic• Where and when did clusters occurred?

Results and Conclusions

We will show that:1. There were areas and times at highest risk for

disease and that disease spread on specific directions

2. Cases neighbored other cases (<20thand <4th order of neighborhood in NC and IA, respectively)

3. Clustering was maximum within 1 week, high within 2 weeks, and still significant within 3 weeks.

4. Clustering increased linearly, up to 1 mile, and then remained stable

North Carolina

• Data from most (>70%) farms in 4 counties (>2000)– 59% finishing, 21% nursery, 15% farms with sows

• 614 positive sites (30%) (54.6% lateral)• Report of cases– Start: July-2013– End: Jan-2014

2 months

Location and direction

• Five significant clusters:– “Early stage”– “Dissemination” stage

• Highly significant trend towards NE:33.8°

CE: Order of neighborhood

• NC: cases largely clustered (time not considered)

Knox test (critical time and distance)

Time (d)Space (km)

Pairs of cases

Observed-to-expected ratio

Iowa

• Data from four companies (>400 sites)– 50% finishing, 6% nursery, 42% farms with sows

• Several counties (majority of sites there)• 156 positive sites (37%) (73% lateral)• Cases– Start: May-2013– End: Feb-2014

5 months

• 2 significant clusters– Dissemination stage

• 8 cases in four days (0.64 expected!)

– Late stage

• Highly significant trend towards SE: 322 °

Location and direction

• Cluster at the first levels of neighborhood (k=4)

CE: Order of neighborhood

Knox test (critical time and distance)

Time (d)Space (km)

Observed-to-expected ratio

Pairs of cases

Results and Conclusions

We showed that:1. There were areas and times at highest risk for

disease and that disease spread on specific directions

2. Cases neighbored other cases (<20thand <4th order of neighborhood in NC and IA, respectively)

3. Clustering was maximum within 1 week, high within 2 weeks, and still significant within 3 weeks.

4. Clustering increased linearly, up to 1 mile, and then remained stable

Thank you!Andres Perez Associate Professor

Julio AlvarezResearch Associate

Javier SarradellVisiting Professor

Ana Alba Visiting Researcher

Barbara Brito Research Specialist

Pablo Valdes Research Specialist

Amy KinsleyResearch assistant

Gabe AlGhalithResearch assistant