Acute flaccid myelitis (AFM), a rare condition that causes a polio-like paralysis, has been circulating across the United States. As of September 30, there have been 38 confirmed cases reported to the Centers for Disease Control and Prevention (CDC), which have occurred in 16 states, but the numbers appear to be growing.
In Washington state, six children have now presented with a sudden onset of paralysis of one or more of their limbs. The latest case was reported to the Washington State Department of Health on Thursday, October 11, and came out of Skagit County, which lies north of Seattle. All reported cases are in counties in Western Washington.
Also on Thursday, hospital officials from Oishei Children’s Hospital in Buffalo, New York, have confirmed that physicians are treating a 3-year-old patient with a “highly suspected” case of AFM. The child and his family have been “in and out of the hospital the past two weeks and now, the boy is unable to walk,” WKBW in Buffalo reports.
While the hospital has completed its own testing for AFM, samples have been sent to the CDC for further evaluation.
Affected states include California, Colorado, Florida, Illinois, Massachusetts, New York, Pennsylvania, Rhode Island, Texas, Virginia, and Washington.
True Numbers Hard to Determine
From August 2014 through August 2018, the CDC has been notified of 362 cases of the illness, mostly in children. But even though the official number of cases is 38 for 2018 (as of September 30), it may not reflect the actual number that will eventually be confirmed.
For example, Minnesota has reported six cases; three children are being treated in Pittsburgh; two are being treated in Chicago; and eight cases have been reported in Texas, one in Rhode Island, and 14 in Colorado.
However, the 38 cases reported by the CDC do not include all of the 14 cases announced by Colorado, as some were confirmed after September 30. It also doesn’t include those from Minnesota, as they have also not yet been confirmed. In addition, nine cases have been reported in children in northern Illinois, but they too have not been confirmed by the CDC.
The CDC began actively investigating AFM in August 2014, when it noticed an increase in reports of people across the country presenting with AFM but without a discernible cause. In 2014, a total of 120 cases were reported, spread out over 34 states.
The number dropped the following year to 22 cases reported in 17 states, but that dramatically jumped to 149 in 2016, reported in 39 states and the District of Columbia. The following year, the number decreased again to 33 cases in 16 states.
The underlying cause of many of this year’s cases has not yet been identified. The sharp increase in AFM cases in 2014 coincided with an outbreak of severe respiratory illnesses caused by enterovirus D68 (EV-D68). However, EV-D68 was not detected in all individuals with confirmed AFM. During 2015, the CDC did not receive any reports of large EV-D68 outbreaks, with local laboratories reporting only limited EV-D68 detections. The following year, a few localized clusters were reported.
Different Enterovirus Seen in Colorado
While EV-68 has been associated with this syndrome, in Colorado far more cases have been linked to infection with enterovirus A71 (EV-A71). According to the Colorado Department of Public Health and Environment (CDPHE), there have been 41 cases of EV-A71 infections tied to neurologic illnesses in young children this year. Of those cases, 14 have involved AFM, and 11 of the AFM cases have tested positive for EV-A71. Only one child tested positive for EV-D68, and two were EV-negative.
“We have been conducting surveillance in Colorado for enteroviruses for a number of years, which may be the reason that we have observed some of these trends,” Rachel Herlihy MD, MPH, state epidemiologist at CDPHE, told Medscape Medical News. “Back in 2003 and 2005, we did detect cases of EV-A71, which were identified by the children’s hospital.”
Those were cases that did involve neurologic illness in children, she explained. “In 2014, Colorado, along with other parts of the country, had a much wider outbreak of EV-D68 that was associated with AFM. We had 11 cases that year in Colorado. So this year it’s different from what we had in 2014, but the same as what we had in 2003 and 2005.”
The clinical course and presentation with EV-A71 is also quite different from that of EV-D68, Herlihy said. “Children with A71 do not present with a respiratory illness, and instead, they may have a rash, diarrhea, or a fever. D68 is associated with a respiratory illness that may be followed by AFM.”
In Washington state, all of the children presented with symptoms indicative of a respiratory illness the week before they developed symptoms of AFM. Four children also had a fever of at least 100.4 degrees, but these symptoms do not precede all individuals who develop AFM. These differences make the problem harder to categorize around the country.
“I don’t think we know which enterovirus is causing the cases — it may be D68 in other parts of the country, but again, we are not seeing that in Colorado,” Herlihy said.
Any virus can cause neurological symptoms, the CDC says, and several have been linked with the paralyzing condition. To date, no specific pathogen has been consistently detected in the cerebral spinal fluid of affected patients.
The agency also points out that much remains unknown about AFM, such as what prompted the increase in cases that began in 2014. It also remains unclear as to which individuals are at a higher risk of developing AFM, or the reasons why they may be at higher risk.
“There can be diagnostic challenges with enteroviruses,” Herilhy said. “Cerebral spinal fluid is often not positive for enteroviruses, and our recommendation is that providers collect specimens from alternative sites. We are seeing more positive cultures and less false negatives when specimens are collected from three sites — [cerebrospinal fluid], throat and rectal swabs.”