Trends in Respiratory Illness in Illinois Associated with Circulation of Enterovirus D68

BACKGROUND:  In August, 2014 clusters of severe respiratory illness in children were reported in multiple locations throughout Illinois. Enterovirus D68 (EV-D68) was suspected, but during the outbreak it was difficult to obtain laboratory-confirmation to characterize the full extent of the increase in illness. To supplement case reporting, Illinois analyzed data from emergency department (ED) pediatric visits. 

METHODS: Acute respiratory illness in persons under 18 years of age was assessed from statewide ED visit data that is submitted to the National Syndromic Surveillance Platform and data from Northern Illinois hospitals that is also submitted to the Cook County ESSENCE system. Seventy-five percent of all ED visits in Illinois are reported daily. Laboratory-confirmed cases of EV-D68 were detected from specimens submitted voluntarily to Illinois Department of Public Health. The range of onset dates among cases defined the outbreak period. Risk ratios between the outbreak period during 2014 and the same period of time during 2012 and 2013 were calculated to measure risk for specific symptom presentations reported in the chief complaint and diagnosis data, including cough, dyspnea, asthma, and fever. Joinpoint regression analysis was performed to test the trends in the daily percentage of pediatric respiratory illness regionally.  

RESULTS: In Illinois, there were 103 laboratory-confirmed cases of EV-D68 with onset between August 13 and September 21, 2014.  Compared to previous years, during the same time period, there was a significant increase in the risk of cough from 2012 (RR=1.36 95% CI 1.30, 1.42) and 2013 (RR= 1.56 95% CI 1.48, 1.64), asthma exacerbation from 2012 (RR=1.42 95% CI 1.31, 1.54) and 2013 (RR=1.57 95% CI 1.44, 1.71), and dyspnea from 2012 (RR=1.54 95% CI 1.47, 1.62) and 2013 (RR=1.68 95% CI 1.60, 1.77), though there was not a significant increase in fever from 2012 (RR=0.98 95%CI 0.94, 1.12) and 2013 (RR=0.89 95% CI 0.85, 0.92). Trends in respiratory illness regionally during the 2014 outbreak were significantly different from the overall state trend in the regions of Peoria (p=0.0002), Edwardsville (P=0.0002), Bellwood (0.0002) and West Chicago (p=0.0011), representing the Western and Northeastern parts of the state. 

CONCLUSIONS: Timely ED visit data provided an assessment of the symptom presentation and spatial and temporal patterns of acute respiratory illness in children during the Enterovirus D68 outbreak in Illinois. Trends can be impacted by several factors, including presence of other circulating respiratory viruses, changing seasonal and behavior patterns or increased education and awareness of disease incidence.