The Centers for Disease Control and Prevention on Tuesday appealed to doctors to rapidly report suspected cases of a mysterious ailment that afflicts young children, saying delays in identifying possible cases of acute flaccid myelitis, or AFM, are hindering the search for the condition’s cause.

Every two years since 2014, a surge of the polio-like illnesses has struck a number of young children across the country, leaving them with weakened limbs. Efforts to find the cause of the phenomenon have pointed to viral infections as a possible culprit, but to date no one virus has been clearly implicated.

Dr. Tom Clark, deputy director of CDC’s division of viral diseases, said the agency needs to hear about these cases while they are being investigated in hospital, not after the fact. Sometimes cases are not reported for months, he said.

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“The kid may have gone home [from hospital] before we’re even notified. It’s not ideal for us,” Clark told STAT. “This delay in reporting kind of hamstrings our efforts to systematically do the right laboratory testing.”

The delay can affect the types of samples taken from the children. Instead of getting quality specimens with enough material to test, sometimes the CDC finds itself with “specimen remainders,” Clark said.

“When we try to bring new approaches to bear, new ways to try to get at the cause of AFM, you’re sort of left with this hodgepodge of specimens,” he said. “So we’re really trying to make the case that it’s rapid recognition and reporting that will help us systematically collect the best specimens early enough to advance our understanding of what’s causing the AFM.”

On Tuesday, the CDC also published an update of its investigation into AFM cases that were identified during the 2018 season, the third wave of cases the country has seen.

AFM cases chart
Most patients had onset of AFM between August and October, with increases in AFM cases every two years since 2014. CDC

While these cases can occur at any time, and in any year, there seems to be an increase in cases on alternate years in the late summer and early autumn. In 2018, the largest wave so far, there were 232 confirmed cases of AFM and 26 probable cases. An additional 109 cases reported to the CDC were eventually ruled out as not being AFM. None of the 2018 cases died, the report said.

Children who are affected by the condition — the median age of cases is about 5 years old — typically suffer from a respiratory or diarrheal illness shortly before experiencing muscle weakness. The muscle weakness often sets in rapidly, with some reports of children waking up and finding themselves unable to move one or some limbs. The condition often affects the arms.

Most children with the condition end up hospitalized, with about 60% being admitted to intensive care; about a quarter of confirmed cases are put on a ventilator to help them breathe for a time.

The first observed wave, which occurred in 2014, coincided with a large outbreak of infections with an enterovirus called EV-D68, as did the 2018 wave. The virus that causes polio is also in the enterovirus family. Several of the AFM cases over the years have shown signs of recent infection with another enterovirus, EV-A71, or with rhinoviruses, which cause common colds.

Efforts to look for viral culprits in the spinal fluid of cases have also occasionally led to positive findings, but rarely. Only two of the 2018 cases for which there was spinal fluid to test were positive for an enterovirus, the CDC report said.

Clark said the thinking is that testing may be happening too late — that the damage the infection has triggered has already occurred by the time nostrils are swabbed or spinal fluid is drawn to look for viruses.

“The real key is that when we look in the spinal fluid, case after case after case you almost never find anything,” he said. “If you keep looking for enterovirus or other viruses in the spinal fluid using the same methods, you’re probably going to continue to not find it very frequently. And that’s either because it’s not there … or it was there but now it’s gone. So you need to find new ways to look.”

One such way, recently reported in STAT, is to look for antibodies to enteroviruses and other pathogens in spinal fluid. It’s a bit like acknowledging that if the horse has already left the barn, evidence of the horse’s previous presence may be the way to answer the question.

But this and other approaches require that clinicians looking after children suspected of suffering from AFM think to alert public health officials from the earliest moments of their hospital admission. Clark noted that these children are probably being treated by neurologists, who may not be accustomed to reporting to public health officials in the way infectious diseases physicians would.

“They’re doing the right things. They’re admitting the kids, putting them in the ICU, doing the MRIs, giving spinal taps. [But] among the many things they’re doing, picking up the phone and calling the health department is not one,” he said. “We want to make it one of the things they’re doing.”

Dr. John Williams, chief of the division of pediatric infectious diseases at UPMC Children’s Hospital of Pittsburgh, said another factor contributing to the delay in reporting could be that many children in the country are cared for at community hospitals, where they may not be seen by pediatric neurologists or pediatric infectious disease specialists. In these cases, doctors may not be aware of the recent unusual pattern of AFM cases, Williams said.

“We’re all waiting to see what happens this summer and next summer. And I think in 2020 a lot of physicians in any specialty that sees children — neurologists, ER docs, ID docs, pediatricians, family practitioners — they’ll all be thinking of this,” Williams said, whose hospital is part of a network that works with the CDC to conduct surveillance for respiratory and intestinal diseases. He said AFM is being added to the conditions the network is looking for.

The CDC also wants to ensure the medical community does not assume that AFM cases will decline this fall because of the large number of cases in 2018.

“The message is that we are prepared for another outbreak season, should that happen,” Clark said. “And we’re sort of preparing as if 2019 could be an outbreak season, though if the pattern holds it won’t be.”

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