The Centers for Disease Control and Prevention warned parents and caregivers Tuesday to watch out for an uncommon, polio-like condition that mostly strikes children, usually between August and November.

Acute flaccid myelitis, which may be caused by any of several viruses, is marked by a sudden weakness or paralysis of the limbs. Since surveillance began in 2014, prevalence of the ­syndrome has spiked in even-numbered years, often afflicting children about 5 years old.

The disease is very rare, but a quick response is critical once the weakness sets in; the disease can progress over hours or days and lead to permanent paralysis or respiratory failure, according to a report issued Tuesday by the CDC. Among 238 cases in 2018 reviewed by the CDC, 98 percent of patients were hospitalized, 54 percent required intensive care, and 23 percent were placed on ventilators to help them breathe.

Most patients were hospitalized within a day of experiencing weakness, but about 10 percent were not hospitalized until four or more days later, possibly because of failure to recognize the syndrome, the report said.

Limb weakness, difficulty walking and limb pain are often preceded by fever or respiratory illness, usually by about six days, the CDC said. Hundreds of U.S. children have been affected, and many do not fully recover.

A number of viruses — including West Nile virus, adenovirus and non-polio enteroviruses — are known to produce the symptoms in a small number of people who become infected by those pathogens. But enterovirus, particularly one dubbed EV-D68, appears to be the most common cause, the CDC said. The National Institute of Allergy and Infectious Diseases is working on a vaccine for EV-D68.

Thomas Clark, the deputy director of the CDC’s division of viral diseases, said the coronavirus pandemic may force doctors to evaluate patients by phone or telemedicine, but he warned that they should not delay if they suspect the syndrome, which is considered a medical emergency.

It is unclear whether mask-wearing, social distancing and other measures that have been taken against the coronavirus will limit the outbreak of acute flaccid myelitis expected this year.