Establishing the baseline burden of influenza in preparation for the evaluation of a countywide school-based influenza vaccination campaign.
BACKGROUND
School-based influenza vaccination campaigns could mitigate the effects of influenza epidemics. A large countywide school-based vaccination campaign was launched in Knox County, Tennessee, in 2005. Assessment of campaign effects requires identification of appropriate control populations. We hypothesized that contiguous counties would share similar pre-campaign patterns of influenza activity.


METHODS
We compared the burden of influenza emergency department (ED) visits and hospitalizations between Knox County (Knox) and eight counties surrounding Knox (Knox-surrounding) during five consecutive pre-campaign influenza seasons (2000-01 through 2004-05). Laboratory-defined influenza seasons were used to measure the weekly incidence of medically attended acute respiratory illnesses (MAARI) attributable to influenza in school-aged children 5-17 years old (campaign target) as well as in other age groups. Seasonal rates of MAARI attributable to influenza for Knox and Knox-surrounding counties were compared using rate ratios.


RESULTS
During five consecutive influenza seasons, MAARI attributable to influenza showed synchronous temporal patterns in school-aged children from Knox and Knox-surrounding counties. The average seasonal rates of ED visits attributable to influenza were 12.37 (95% CI: 10.32-14.42) and 13.14 (95% CI: 11.23-15.05) per 1000, respectively. The respective average seasonal influenza hospitalization rates for Knox and Knox-surrounding were 0.38 (95% CI: 0-0.79) and 0.46 (95% CI: 0.07-0.85) per 1000 children. Rate ratio analyses indicated no significant differences in the incidence of MAARI attributable to influenza between school-aged children from Knox and Knox-surrounding counties. Estimates for other age groups showed similar patterns.


CONCLUSIONS
Before the Knox school-based influenza vaccination campaign, influenza resulted in an average of about 12 ED visits and 0.4 hospitalizations per 1000 school-aged children annually in Knox County. Since similar morbidity was observed in surrounding counties, they could serve as a control population for the assessment of the campaign effects.
Department of Preventive Medicine, Vanderbilt University School of Medicine, Nashville, TN, United States. carlos.grijalva@vanderbilt.edu
Carlos G
CG
Grijalva
Yuwei
Y
Zhu
Lone
L
Simonsen
Marie R
MR
Griffin
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000553:Ambulatory Care / Q000706:statistics & numerical data; D002648:Child; D002675:Child, Preschool; D004632:Emergency Medical Services / Q000706:statistics & numerical data; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D015994:Incidence; D007252:Influenza Vaccines / Q000008:administration & dosage*; D007251:Influenza, Human / Q000175:diagnosis / Q000453:epidemiology* / Q000517:prevention & control* / Q000821:virology; D008297:Male; D008875:Middle Aged; D009975:Orthomyxoviridae / Q000302:isolation & purification; D012574:Schools; D013334:Students; D013714:Tennessee / Q000453:epidemiology; D014611:Vaccination / Q000379:methods*; D055815:Young Adult
D007252:Influenza Vaccines