Patterns, Characteristics of Children Diagnosed With Acute Flaccid Myelitis Between 2014 and 2020

Medic shows diagnosis Acute Flaccid Myelitis AFM.
Researchers conducted a study that compared the patterns and characteristics of acute flaccid myelitis among patients diagnosed in peak years vs those diagnosed in nonpeak years.

In 2020, the number of new diagnoses of acute flaccid myelitis (AFM) did not increase as expected, which may have resulted from social distancing measures, use of face masks, and decreased in-person school attendance. These findings were published in the Morbidity and Mortality Weekly Report.

Researchers conducted a national surveillance study that assessed AFM diagnoses among children in the United States between 2014 and 2020. After the implementation of a national AFM surveillance program in 2014, biennial increases in AFM diagnoses were observed in 2014, 2016, and 2018. AFM causes respiratory insufficiency leading to permanent paralysis among previously healthy children.

To describe the characteristics of patients who were diagnosed with AFM between 2018 and 2020, the researchers analyzed patients’ electronic health records and laboratory results. In 2018, 2019, and 2020, a total of 238, 47, and 32 patients with confirmed diagnoses of AFM were reported to the Centers for Disease Control and Prevention (CDC), respectively. Among patients diagnosed with AFM in 2018 and 2019, analysis of respiratory and stool specimens showed enterovirus D68 (EV-D68) in 37, 1, and 0, respectively.

Compared with patients diagnosed with AFM in 2018, the researchers found that AFM diagnoses in 2019 (n=47) and 2020 (n=32) were more likely to occur in older children (median age, 9.2 vs 6.6 and 5.3 years, respectively). In addition, they noted that the frequency of upper limb involvement, febrile or respiratory prodromal illness, and cerebrospinal fluid pleocytosis was decreased among patients diagnosed with AFM in 2019 and 2020 vs those diagnosed in 2018.

Among patients diagnosed with AFM between 2018 and 2020, 98% to 100% were hospitalized, 51% to 59% were admitted to an intensive care unit, and 16% to 28% required intubation and mechanical ventilation. Of note, the proportion of patients with AFM who were hospitalized within 1 day of their diagnosis increased between 2018 and 2020. On specimen analysis, EV-A71 was detected among 13, 2, and 1 patient(s) diagnosed with AFM in 2018 and 2019, and 2020, respectively. In addition, rhinovirus was detected among 10, 1, and 3 patients who were diagnosed with AFM in 2018, 2019, and 2020, respectively.

The researchers noted that measures to decrease the spread of the SARS-CoV-2 virus in 2020 may have also decreased the spread of AFM-associated viruses. Although AFM diagnoses in peak years were more frequently associated with EV-D68, the researchers noted that AFM diagnoses in nonpeak years were associated with a mixture of etiologies.

This study was limited by its inclusion of only patients with AFM who were reported to the CDC, which may not have represented the actual number of AFM diagnoses that occurred in the US.

The researchers noted that “AFM should be suspected in any child with acute flaccid limb weakness, especially among those with a recent history of febrile or respiratory illness.” They concluded that “clinicians should remain vigilant for this condition in 2021 and report potential cases (of AFM) to their public health department.”


Kidd S, Yee E, English R, et al. National surveillance for acute flaccid myelitis-United States, 2018-2020. Morb Mortal Wkly Rep. 2021;70(44):1534-1538. doi:10.15585/mmwr.mm7044a2