US Outbreaks Of
Acute Flaccid Myelitis Still Posing Several Mysteries
Identifying Risk
Factors Called “A Public Health Priority”
A comprehensive review and analysis in July by the
Centers for Disease Control and Prevention (CDC ) of cases of acute
flaccid myelitis (AFM) which causes limb weakness mostly in children
reveals many unsolved mysteries (MMWR, July 12). CDC Principal Deputy
Director Anne Schuchat speaking at a recent telebriefing said
“AFM is a devastating illness for patients and their families…and we
want parents to know that we are keeping their children front and
center and working with our partners to better understand this
illness, the risk factors, and ways to treat and prevent it.” The
unanswered epidemiologic questions are a cause of concern at the CDC
which has declared the identification of risk factors for AFM a public
health priority.
The disease was first recognized as a distinct
condition during a severe outbreak of respiratory illness caused by
enterovirus D-68 (EV-D68) in 2014. Since then, there have been
seasonal peaks between August and October every two years in 2016 and
2018. This seasonality casts suspicion on viruses as the etiologic
agents. Cases are found year round and in the odd-numbered years, but
the reasons for the two-year peaks or periodicity are a mystery.
Laboratory Evidence
While respiratory viruses and enteroviruses in
particular are suspected as the causative agents, the laboratory
evidence is not yet conclusive. Most of the cases have a history of
mild respiratory illness or fever less than a week before they
developed arm or leg weakness. However, approximately half of cases
can be negative for evidence of virus infection in respiratory
specimens.
Recent Development
Another mystery is why the outbreaks have started only
in recent times. AFM is a recognized but rare complication of
infections caused by West Nile virus, adenovirus, and enteroviruses.
However, the first recognized outbreak of AFM was noted in
association with the large US outbreak of severe respiratory illness
caused by EV-D68 in 2014.
The condition is still considered rare with 233
confirmed cases during the 2018 outbreak. Why some children develop
limb weakness and others do not is a puzzle. Perhaps there are genetic
predispositions not yet identified. Affected children have been
previously healthy and nothing unusual about them has been noted to
date.
Recent Publications
The CDC reports about AFM in the MMWR and in Vital
Signs and the telebriefing were timed for the beginning of the 2019
season from August to October when AFM cases have peaked. The CDC goal
is to alert everyone to anticipate cases and to report them as early
as possible to assure thorough investigations that might provide a
better understanding of the epidemiology.
Latest Epidemiology
During 2018, CDC received reports of 374 persons
meeting the case definition for AFM and 233 of these or 62% were
classified as confirmed and 26 or 7% as probable. As many as 115
reported persons were classified as non-AFM cases.
Confirmed cases had a median age of 5.3 years and were
equally distributed by sex. 98% of confirmed cases were hospitalized
and 60% of these were admitted to an intensive care unit. No deaths
were reported during the acute phase of illness among confirmed cases,
but two deaths occurred months after limb weakness onset. Since 2014,
the occurrence of AFM has been very widespread with reports coming
from 48 states.
More Epi Investigation
Needed
According to CDC, “prompt recognition of signs and
symptoms, early specimen collection, and complete and rapid reporting
will expedite public health investigations and research studies to
elucidate the recent epidemiology of
AFM and subsequently inform
treatment and prevention.”
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