The Centers for Disease Control and Prevention (CDC) investigated 33 more acute flaccid myelitis (AFM) cases this past week and confirmed 10 more, bringing the total number of investigated cases in 2018 to 252 in 27 states.
Ninety of those cases are confirmed, and so far there have been no deaths attributed to AFM in 2018.
As in previous outbreak years, including 2014 and 2016, the mysterious, polio-like illness remains an enigma to researchers who are trying to tease out what is causing otherwise healthy children between the ages of 2 and 8 to develop the condition.
In the 3 to 10 days before the onset of weakness or paralysis, the children report fever or upper respiratory illnesses. Then, they experience limb weakness. Some children recover fully, others only partially.
Known or unknown virus?
Nancy Messonnier, MD, director of the CDC's National Center for Immunization and Respiratory Diseases, said the cause of AFM could be a known entity, like an enterovirus or rhinoviruses (EV/RV). Or it could be an unknown virus. Either way, a virus could be triggering an autoimmune repose in some children that causes AFM.
"We're trying to figure out what the triggers are of what causes someone to get AFM," Messonnier said during a CDC press conference today. "Seventy-one of confirmed cases have had specimens tested," said Messonnier. "About half [54%] have tested positive for enterovirus (EV) or rhinovirus, and 2 cases showed pathogens in the spinal cord."
According to a report published today in the CDC's Morbidity and Mortality Weekly Report (MMWR), of the 80 confirmed cases in 2018, testing has been performed on a total of 125 clinical specimens from 71 (89%) patients, including 21 cerebral spinal fluid (CSF), 59 upper respiratory, and 45 stool/rectal swab specimens.
Among 38 patients who tested positive for EV/RV, specimens from 11 (29%) tested positive for EV-A71, 14 (37%) for EV-D68, and 13 (34%) for other viruses, primarily from nonsterile sites. One CSF specimen was positive for EV-A71; another for EV-D68.
Since 2014, the CDC has tested AFM patients' CSF, and only a few have had a pathogen, Messonnier said. Spinal cord pathogens are rare, which means their presence could be indicative of AFM's cause. Nasal swabs that harbor rhinoviruses are less helpful, Messonnier said, as many children—both sick and well—will host a variety of pathogens during the cold and flu season.
AFM appears to occur seasonally, in the fall, and appears only sporadically until an outbreak year. In 2014, officials confirmed 120 cases in the United States, but only 22 in 2015. In 2016, confirmed cases jumped to 149. The 2014 outbreak was initially linked to EV-D68, a strain of enterovirus that can cause paralysis (see today's news scan), but subsequent outbreak years haven't provided the same evidence.
Challenges for local health departments
Messonnier said the CDC is working on streamlining the AFM diagnostic process and tracking long-term outcomes. She said the agency hopes both efforts will help provide a clearer picture of what's causing AFM.
It can take 1 to 3 weeks before the CDC confirms if a child's paralysis is AFM. First, a clinician must report a suspected case to the local health department, and then the health department reports the case to the CDC. The CDC defines diagnosis with AFM as limb weakness or paralysis with the presence of spinal cord lesions on magnetic resonance imaging.
So far, no federal or state agency tracks the long-term outcomes of confirmed cases, and there are no targeted therapies or interventions designed for AFM.
"As a mom myself I can understand why people are worried; I'm concerned about the rise," Messonnier said. "But we should remember: AFM is still extremely rare."
Jayne Griffith, MA, MPH, the lead epidemiologist at the Minnesota Department of Health working on a cluster of AFM cases in Minnesota, said her goal has been reaching out to clinicians.
"We've done a statewide call on clinical characteristics to push the information out," Griffith said. Minnesota has 7 cases of AFM this fall, and one case that occurred in July, for a total of 8 cases in 2018. In 2014, the state saw only 3 cases, with no cases reported in 2015 and 2016 and only 1 last year. Griffith said the Minnesota patients are showing a range of recovery in the current outbreak.
"The number of cases are still fairly low to be able to make specific inferences about the cause of AFM," said Griffith. "But we have a desire to learn from the current outbreak."
Nov 13 MMWR report
CDC confirmed AFM cases by month of onset