In 2014, 2016, and 2018, the United States saw an uptick in enterovirus-D68 (EV-D68) infections and a subsequent rise in acute flaccid myelitis (AFM) cases, a severe neurologic condition that can result in paralysis.
The pandemic likely disrupted the biannual pattern of infection in 2020, but an uptick in EV-D68 respiratory illnesses in 2022 did not lead to a matching increase in AFM cases, according to findings in Morbidity and Mortality Weekly Report. AFM cases have remained low since 2018, for reasons unknown, the authors said.
The Centers for Disease Control and Prevention (CDC) has monitored AFM cases annually by tracking case reports of acute flaccid limb weakness with any spinal-cord gray-matter lesion on magnetic resonance imaging. During 2018, 2019, 2020, 2021, and 2022, a total of 238, 47, 33, 28, and 47 confirmed AFM cases, respectively, were reported to the CDC.
No EV-D68 found in recent AFM cases
The average age of AFM patients has also increased since 2018, from 5.1 years to 8 years in 2021 and 7.1 years in 2022. AFM cases after 2018 also had less upper-body paralysis and febrile illness. And despite widely circulating EV-D68 causing respiratory illness in 2022, EV-D68 was detected in no patents with AFM in 2020 through 2022.
"Despite apparently increased EV-D68 circulation and EV-D68–associated respiratory disease among children, the reason why an increase in AFM cases did not occur in 2022 is unclear; possibly, EV-D68 viruses circulating in 2022 were less neurotropic or less likely to cause neurologic disease than were viruses circulating during 2014, 2016, and 2018," the authors wrote.
Despite apparently increased EV-D68 circulation and EV-D68–associated respiratory disease among children, the reason why an increase in AFM cases did not occur in 2022 is unclear.
The authors also said co-circulating respiratory viruses in 2022, including respiratory syncytial virus (RSV) and COVID-19, may have affected immune responses to EV-D68 and provided protection against neurologic disease.