A Pre-Pandemic Outbreak of Triple-Reassortant Swine Influenza Virus Infection Among University Students, South Dakota, 2008
Fatimah S. Dawood1,2, Libo Dong1,a, Feng Liu1, Dianna M. Blau3, Patrick J. Peebles1, Xiuhua Lu1, Lori Wagers4, Brett Oakland4, Michael Zielenski4, Russell Daly5, Vickie Horan4, Sabrina L. Swenson6, Beverly J. Schmitt6, Kathy Hancock1, Jacqueline M. Katz1, Carolyn Bridges1, Lon Kightlinger4 and Lyn Finelli1
+ Author Affiliations
1Influenza Division
2Epidemic Intelligence Service, Office of Workforce and Career Development, and
3Infectious Diseases Pathology Branch, Centers for Disease Control and Prevention, Atlanta, Georgia
4South Dakota Department of Health, Pierre; and
5South Dakota State University, Brookings
6National Veterinary Services Laboratories, Ames, Iowa
Correspondence: Fatimah S. Dawood, MD, Epidemic Intelligence Service Officer assigned to the Influenza Division, Centers for Disease Control and Prevention, 1600 Clifton Rd, MS A-32, Atlanta, GA 30333 (
fdawood@cdc.gov).
Abstract
Background. After identifying a student with triple-reassortant swine influenza virus (SIV) infection and pig exposure at a livestock event, we investigated whether others were infected and if human-to-human transmission occurred.
Methods. We conducted a cohort study and serosurvey among persons exposed to (1) event pigs, (2) other pigs, (3) the index case, and (4) persons without pig or index case exposure. Confirmed cases had respiratory specimens positive for SIV within 2 weeks of the index case’s illness. Probable and suspected cases had illness and (1) exposure to any pig or (2) contact with a confirmed case preceding illness. Probable cases were seropositive. Suspected cases did not give serum samples.
Results. Of 99 event pig-exposed students, 72 (73%) participated in the investigation, and 42 (42%) provided serum samples, of whom 17 (40%) were seropositive and 5 (12%) met case criteria. Of 9 students exposed to other pigs, 2 (22%) were seropositive. Of 8 index case-exposed persons and 10 without exposures, none were seropositive. Pig-exposed persons were more likely to be seropositive than persons without pig exposure (37% vs 0%, P < .01).
Conclusions. We identified an outbreak of human SIV infection likely associated with a livestock event; there was no evidence of human-to-human transmission.
Received February 10, 2011.
Accepted May 12, 2011
http://jid.oxfordjournals.org/content/204/8/1165.short
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