Spatial Epidemiology of PED Virus - Dr. Andres Perez, University of Minnesota, Associate Professor, Veterinary Population Medicine, from the 2014 Allen D. Leman Swine Conference, September 15-16, 2014, St. Paul, Minnesota, USA. More presentations at http://www.swinecast.com/2014-leman-swine-conference-material

1. Andres Perez
Associate Professor, CVM, UMN
aperez@umn.edu
Spatial epidemiology of PED
2014 Allen D. Leman Swine Conference
Pre-conference workshop
September 13, 2014
St. Paul RiverCentre, St. Paul, Minnesota

2. Introduction

3. 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

4. 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?

5. 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

6. 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

7. Location and direction
• Five significant clusters:
– “Early stage”
– “Dissemination” stage
• Highly significant trend
towards NE:33.8°

8. CE: Order of neighborhood
• NC: cases largely clustered
(time not considered)

9. Knox test (critical time and distance)
Time (d)
Space (km)
Pairs of cases
Observed-to-
expected ratio

10. 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

11. • 2 significant clusters
– Dissemination stage
• 8 cases in four days (0.64
expected!)
– Late stage
• Highly significant
trend towards SE:
322 °
Location and direction

12. • Cluster at the first levels of neighborhood (k=4)
CE: Order of neighborhood

13. Knox test (critical time and distance)
Time (d)
Space (km)
Observed-to-
expected ratio
Pairs of cases

14. 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

15. Thank you!
Andres Perez
Associate Professor
Julio Alvarez
Research Associate
Javier Sarradell
Visiting Professor
Ana Alba
Visiting Researcher
Barbara Brito
Research Specialist
Pablo Valdes
Research Specialist
Amy Kinsley
Research assistant
Gabe AlGhalith
Research assistant