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Expected spike in acute flaccid myelitis did not occur in 2020



The anticipated biennial peak in acute flaccid myelitis cases did not occur in 2020, possibly because of “nonpharmaceutical interventions implemented during the COVID-19 pandemic,” suggested researchers at the Centers for Disease Control and Prevention.

Number of confirmed cases of acute flaccid myelitis by month

Acute flaccid myelitis (AFM) is an uncommon but serious complication of some viral infections, including West Nile virus and nonpolio enteroviruses. It is “characterized by sudden onset of limb weakness and lesions in the gray matter of the spinal cord,” they said, and more than 90% of cases occur in young children.

Cases of AFM, which can lead to respiratory insufficiency and permanent paralysis, spiked during the late summer and early fall in 2014, 2016, and 2018 and were expected to do so again in 2020, Sarah Kidd, MD, and associates at the division of viral diseases at the CDC’s National Center for Immunization and Respiratory Diseases, Atlanta, said in the Morbidity and Mortality Weekly Report.

Monthly peaks in those previous years – each occurring in September – reached 51 cases in 2014, 43 cases in 2016, and 88 cases in 2018, but in 2020 there was only 1 case reported in September, with a high of 4 coming in May, CDC data show. The total number of cases for 2020 (32) was, in fact, lower than in 2019, when 47 were reported.

The investigators’ main objective was to see if there were any differences between the 2018 and 2019-2020 cases. Reports from state health departments to the CDC showed that, in 2019-2020, “patients were older; more likely to have lower limb involvement; and less likely to have upper limb involvement, prodromal illness, [cerebrospinal fluid] pleocytosis, or specimens that tested positive for EV [enterovirus]-D68” than patients from 2018, Dr. Kidd and associates said.

Mask wearing and reduced in-school attendance may have decreased circulation of EV-D68 – the enterovirus type most often detected in the stool and respiratory specimens of AFM patients – as was seen with other respiratory viruses, such as influenza and respiratory syncytial virus, in 2020. Previous studies have suggested that EV-D68 drives the increases in cases during peak years, the researchers noted.

The absence of such an increase “in 2020 reflects a deviation from the previously observed biennial pattern, and it is unclear when the next increase in AFM should be expected. Clinicians should continue to maintain vigilance and suspect AFM in any child with acute flaccid limb weakness, particularly in the setting of recent febrile or respiratory illness,” they wrote.

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