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Cases of acute flaccid myelitis (AFM), a rare polio-like condition that affects mainly children, remained low in 2019 and 2020, CDC data showed.

Peak cases of AFM occurred in 2014, 2016, and 2018. Based on that biennial pattern, cases were expected to spike in 2020 but did not, reported Sarah Kidd, MD, of the CDC, and co-authors, in .

"The absence of an increase in cases in 2020 reflects a deviation from the previously observed biennial pattern, and it is unclear when the next increase in AFM should be expected," Kidd and colleagues wrote. "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."

AFM is characterized by the rapid onset of flaccid weakness in one or more limbs and spinal cord gray matter lesions. It has been (EV-D68) in some patients.

In 2018, a total of 238 confirmed AFM cases were reported to CDC, compared with 47 cases in 2019 and 32 in 2020. The number of cases in 2019 and 2020 was consistent with previous non-peak years, the researchers noted.

The show that as of October 29, 2021, 20 AFM cases have been confirmed this year. A total of 670 cases have been confirmed since CDC began tracking AFM in August 2014.

"Nonpharmaceutical interventions implemented during the COVID-19 pandemic (e.g., face masks, physical distancing, and reduced in-person school attendance) might have reduced transmission of EV-D68 and other enteroviruses associated with AFM," Kidd and colleagues wrote.

"EV-D68 is a respiratory enterovirus, and other respiratory viruses such as influenza and respiratory syncytial virus (RSV) were noted to have decreased circulation during 2020," the team added.

Compared with 2018, cases reported in 2019 and 2020 occurred in older children and were associated less frequently with upper limb involvement, febrile or respiratory prodromal illness, or cerebrospinal fluid pleocytosis.

In patients with confirmed AFM who were tested in 2018, enterovirus/rhinovirus (EV/RV) was found in 50%, and EV-D68 was the most common EV/RV type detected. Although a similar proportion of AFM patients were tested each year, EV/RV was seen in only 37% of 2019 cases and 26% of 2020 cases. EV-D68 was detected in specimens from 37 cases in 2018, one case in 2019, and none in 2020.

"These findings suggest that the etiologies of AFM in 2019 and 2020 differed from those in 2018," Kidd and co-authors observed.

Nearly all patients with confirmed AFM during 2018–2020 were hospitalized, 51% to 59% were admitted to an intensive care unit, and 16% to 28% required intubation and mechanical ventilation. The emergency department was the most common place where cases presented.

Regardless of etiology, AFM can progress rapidly and lead to respiratory insufficiency that requires intubation and mechanical ventilation, the researchers pointed out. "Persons with signs and symptoms of AFM should be immediately hospitalized and their respiratory status monitored."

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