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The number of new cases under investigation continues to slow - likely signaling that the peak of this year's outbreak has passed - but the CDC confirmed 28 additional confirmed cases of acute flaccid paralysis last week, raising this year's total to 158; breaking 2016's previous record of 149.
Many of these new cases are from the backlog of patients under investigation (PUIs), with onsets in August, September, and October.Even though the number of new onset cases continues to decline, back filling when PUIs are confirmed will likely continue for several more weeks.
We are seeing a similar catch-up pattern in Canada, where last week in Acute Flaccid Myelitis In Canada - CMAJ Review, we saw the PHAC had 63 total cases under investigation, with 31 confirmed.
Today, the total number has only increased by 1, but six new cases (n=37) have now been confirmed.While the precise cause of these polio-like outbreaks remain a mystery, a number of enteroviruses (EV-71, EV-D68, etc.) are high on the suspect list. The CDC notes, however, that most cases have tested negative for any virus.
Paralysis - while exceedingly rare - can appear days or even weeks following a suspected viral infection, which may help explain the lack of positive lab tests.It is also possible that this paralysis is due to some sort of autoimmune response to more than one virus, or even that some unknown virus - not currently picked up by testing - is at work.
Some snippets from this week's surveillance update:
AFM Investigation
What CDC has learned since 2014
- Most of the patients with AFM (more than 90%) had a mild respiratory illness or fever consistent with a viral infection before they developed AFM.
- Viral infections such as from enteroviruses are common, especially in children, and most people recover. We don’t know why a small number of people develop AFM, while most others recover. We are continuing to investigate this.
- These AFM cases are not caused by poliovirus; all the stool specimens from AFM patients that we received tested negative for poliovirus.
- We detected coxsackievirus A16, EV-A71, and EV-D68 in the spinal fluid of four of 458 confirmed cases of AFM since 2014, which points to the cause of their AFM. For all other patients, no pathogen (germ) has been detected in their spinal fluid to confirm a cause.
- Most patients had onset of AFM between August and October, with increases in AFM cases every two years since 2014. At this same time of year, many viruses commonly circulate, including enteroviruses, and will be temporally associated with AFM.
- Most AFM cases are children (over 90%) and have occurred in 46 states and DC
(SNIP)
AFM Cases in the U.S.
So far in 2018, there are 158 confirmed cases of AFM in 36 states. These 158 confirmed cases are among the total of 311 reports that CDC received of patients under investigation (PUIs). CDC and state and local health departments are still investigating some of these PUIs.
The case counts represent only those cases for which information has been sent to and confirmed by CDC.
- In 2017, CDC received information for 35 confirmed cases of AFM in 16 states.
- In 2016, CDC received information for 149 confirmed cases of AFM in 39 states and DC.
- In 2015, CDC received information for 22 confirmed cases of AFM in 17 states.
- From August to December 2014, CDC received information for 120 people confirmed cases of AFM in 34 states.
(SNIP)
Prevention
Poliovirus and West Nile virus may sometimes lead to AFM.
While we don’t know if it is effective in preventing AFM, washing your hands often with soap and water is one of the best ways to avoid getting sick and spreading germs to other people. Learn about when and how to wash your hands.
- You can protect yourself and your children from poliovirus by getting vaccinated.
- You can protect against bites from mosquitoes, which can carry West Nile virus, by using mosquito repellent, staying indoors at dusk and dawn (when bites are more common), and removing standing or stagnant water near your home (where mosquitoes can breed).
For more information on what CDC is doing, see our AFM Investigation page.
A few recent studies on the possible causes of AFM include:
mBio: Contemporary EV-D68 Strains Have Acquired The Ability To Infect Human Neuronal Cells
Notes from the Field: Enterovirus A71 Neurologic Disease in Children — Colorado, 2018
Eurosurveillance Review: Association Between Acute Flaccid Myelitis (AFM) & Enterovirus D68 (EV-D68)
