Discussion
Across all study sites, detection of EV-D68 in respiratory specimens collected from patients with ARI remained low during 2019 and 2020, accounting for 0.4% and 3.6% of RV/EV detections, respectively compared with 24.3% of RV/EV detections during 2018. Similar to 2019, EV-D68 represented only 0.3% RV/EV detections among NVSN sites during July–October 2017.[5] EV-D68 clade D was detected in 2020, whereas clade B3 was detected among NVSN sites in 2018.[5] Because the numbers of EV-D68 detections reported from local and national surveillance both within and outside NVSN during 2014, 2016, and 2018 were higher compared with 2015, 2017, and 2019, a biennial pattern of circulation had been postulated, and high circulation in 2020 was anticipated. Instead, EV-D68 circulation in NVSN in 2020 appeared only slightly higher than that in 2019 and 2017, but notably lower than that in 2018, with some variations in 2020 by site. As reported for other respiratory viruses,[6] the lower EV-D68 circulation observed in 2020 might reflect interrupted transmission resulting from COVID-19 mitigation measures including wearing a mask, physical distancing, attention to hand hygiene, and school closures. However, the long-term stability of this biennial pattern of EV-D68 circulation was uncertain even before the COVID-19 pandemic,[7] making the contribution of COVID-19 mitigation measures to low EV-D68 circulation in 2020 unclear. COVID-19 mitigation measures have been theorized to be less effective at reducing RV/EV circulation compared with that of other respiratory virus types because of differences in stability, transmission route, or rates of asymptomatic transmission.[6] More information is needed to better understand which RV/EV species and types persisted in 2020, and why detections of EV-D68 were limited. Furthermore, the implications for future EV-D68 circulation are unknown, and continued monitoring is needed.
Although overall detections of EV-D68 were low, severe respiratory illness was observed in infected patients aged <18 years during 2019 and 2020, with one half of patients requiring inpatient admission. Approximately one half of the patients aged <18 years with EV-D68–positive respiratory specimens in 2020 had underlying asthma/RAD, which has been previously associated with EV-D68.[2] EV-D68–associated severe respiratory illness continues to be a significant medical concern warranting monitoring and preparedness. In addition, EV-D68 is associated with AFM, a rare but debilitating neurologic condition characterized by flaccid limb weakness or paralysis which has been increasingly recognized in recent years.†† Similar to the low number of EV-D68–associated ARI cases in 2020 described in this report, national reports of AFM were also low during 2020.[8]
Among 36 patients aged <18 years with EV-D68 detected in respiratory specimens in 2019 and 2020, most were Black persons or Hispanic persons. Health disparities by race and ethnicity have been reported previously for multiple respiratory viruses,[9] and possibly EV-D68.[10] Additional years of NVSN data are needed to better understand potential health disparities related to EV-D68 infection. Disparities might arise from multiple factors including differences by race in asthma prevalence,§§ differences in access to health care and preventive measures, or higher risk of EV-D68 exposure or severe disease.
The findings in this report are subject to at least four limitations. First, the results are not representative of the entire year and might underestimate EV-D68 detections. However, this report describes EV-D68 testing during July–November when enterovirus detections are highest in the United States. Second, although NVSN surveillance sites are located across the United States, they might not be representative of all regions nationwide. Third, the inclusion of data for only 3 years as well as the small number of EV-D68 detections in 2020 limited multivariable analyses. Finally, NVSN enrollment was lower in 2020, compared with previous years, and health care–seeking behaviors might have been different because of the COVID-19 pandemic.
Circulation of EV-D68 in 2020 might have been limited by widespread COVID-19 mitigation measures, and changing mitigation measures might influence future EV-D68 circulation patterns. Continued monitoring of EV-D68 circulation is critical to guiding clinical and public health preparedness for both EV-D68–associated ARI and AFM.
Acknowledgments
Brian Emery, Shannon Rogers, Aaron Curns, Lynne Shelley.
Morbidity and Mortality Weekly Report. 2021;70(47):1623-1628. © 2021 Centers for Disease Control and Prevention (CDC)
