Vital Signs

Surveillance for Acute Flaccid Myelitis — United States, 2018

Adriana Lopez, MHS; Adria Lee, MPH; Angela Guo, MPH; Jennifer L. Konopka-Anstadt, PhD; Amie Nisler, MPH; Shannon L. Rogers, MS; Brian Emery; W. Allan Nix; Steven Oberste, PhD; Janell Routh, MD; Manisha Patel, MD


Morbidity and Mortality Weekly Report. 2019;68(27):608-614. 

In This Article


Health departments submitted reports of patients meeting the clinical criterion for AFM (acute onset of flaccid limb weakness) to CDC for case classification. For public health surveillance purposes, a confirmed case of AFM was defined as acute flaccid limb weakness in a person with magnetic resonance imaging (MRI) evidence of a spinal cord lesion largely restricted to gray matter and spanning ≥1 spinal segments. Patients with probable AFM met the clinical criterion and had CSF pleocytosis (>5 white blood cells per cubic mm).[10] Patients without documented flaccid limb weakness, with MRI findings that were inconsistent with AFM, or who had alternative diagnoses (e.g., transverse myelitis, acute disseminated encephalomyelitis, Guillain-Barré syndrome, other myelopathy, or spinal stroke) were classified as non-AFM cases.

Health departments and clinicians submitted CSF, respiratory, serum, and/or stool specimens, when available, from patients with suspected AFM to CDC for testing ( In accordance with current clinical, laboratory, and epidemiologic evidence, CDC laboratory protocols included testing of these specimens for enteroviruses, rhinoviruses, and parechoviruses. All specimens were tested for EV/RV using a 5' nontranslated region qualitative real-time reverse transcription–polymerase chain reaction (real-time RT-PCR) pan-enterovirus assay[11] and a pan-enterovirus typing assay by viral protein 1 RT–semi-nested PCR and Sanger sequencing of the resultant amplicon.[12] All specimens were also tested for parechoviruses using a pan-parechovirus real-time RT-PCR assay.[13] Stool specimens were tested for poliovirus by virus isolation in cell culture as part of national poliovirus surveillance. A subset of 31 specimens was also tested at CDC for arboviruses. Results from non-CDC laboratories are not included in this update.

Descriptive analyses of confirmed, probable, and non-AFM cases in patients with onset of limb weakness in 2018 were performed using SAS (version 9.4; SAS Institute). To ascertain early recognition of AFM by clinicians, the number of days from onset of limb weakness to hospitalization and receipt of MRI were compiled. Data from cases confirmed in 2016 and 2018 were compared to evaluate time to hospitalization, collection of specimens, and reporting to CDC. Categorical variables were compared using Chi-squared tests, and medians were compared using the Wilcoxon rank sum test. P-values of <0.05 were considered statistically significant.