If acute flaccid myelitis or AFM follows its usual pattern, 2020 should be a year that sees a spike in US cases -- but the country hasn't seen one yet, according to the US Centers for Disease Control and Prevention.
It's also unclear what impact Covid-19 will have on the rare polio-like condition, which affects the spinal cord and nerves, mostly in children.
The CDC provided an update about AFM in its Grand Rounds meeting Tuesday. It tracks cases each day and has not seen a spike so far, but it may be too early to know. In past years, when there have been outbreaks, case numbers typically peak in September.
As of the end of June, the last time CDC reported numbers, there had been 13 cases in 2020 and 33 cases under investigation.
The first hallmark sign someone has AFM is sudden limb weakness. The polio-like condition occurs mostly in children who are otherwise healthy.
The progression of weakness can happen over hours to a number of days, and can lead to difficulty speaking and swallowing, or it can cause severe respiratory distress. It can also cause lesions on the spinal cord and permanent, sometimes life-threatening, paralysis. About 98% of AFM cases are hospitalized and 54% are placed in the ICU, according to the CDC.
"There is a great deal we don't yet know," Dr. Anne Schuchat, principal deputy director of the CDC, said Tuesday. "We want to do everything possible to learn more about recognizing, treating, and preventing AFM and helping families to heal."
"AFM is a CDC priority," Schuchat added.
It is clear that Covid-19 will have some impact on this AFM cycle, the CDC said.
Social distancing and improved hand hygiene practices may reduce the number of AFM cases, said Dr. Janell Routh, medical officer and lead for the CDC's AFM and Domestic Poliovirus Team.
"These practices may result in a decease circulation of other viruses, including enteroviruses and, therefore, either decrease or delay AFM this year," Routh said.
The pandemic may also impact how the country tracks how many cases there are.
"We don't know if the Covid-19 epidemic will complicate detection and management, nor do we know if the social distancing efforts will reduce the risks of occurrence," said Schuchat. "But we do know we need to be ready."
The CDC and parent groups have been trying to raise awareness among doctors since it was first detected, as it had often been misdiagnosed, some studies have shown. One of the challenges of diagnosis is that the symptoms vary from person to person. It is unclear if some children are more susceptible to more severe forms of the disease. Studies are underway.