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


Since surveillance for AFM began following the 2014 outbreak, nationwide outbreaks have occurred in 2016 and 2018 (Figure 1). From January 1 through December 31, 2018, a total of 374 persons meeting the clinical criterion for AFM were reported to CDC; 233 (62%), from 41 states, were classified as confirmed, 26 (7%) as probable, and 115 (31%) as non-AFM cases (Figure 2). The median age of patients with confirmed AFM, 5.3 years (range = 6 months–81.8 years), was significantly older than that of patients with probable AFM (2.9 years [range = 4 months–55.3 years]; p = 0.04). Patients with illnesses classified as non-AFM were significantly older than were patients with confirmed AFM (median = 8.6 years [range = 1 month–78.1 years]; p<0.001) (Table 1). Sex and race did not differ among patients with confirmed AFM, probable AFM, and non-AFM. Involvement of upper limbs only was significantly more prevalent in patients with confirmed AFM (42%) than in those with non-AFM (10%) (p<0.001). Patients with confirmed and probable AFM more frequently had respiratory symptoms (e.g., cough, rhinorrhea, and congestion) or fever (e.g., temperature ≥100.4°F) (92%) within the 4 weeks preceding limb weakness onset than did patients with non-AFM (62%; p<0.001). Among all patients with confirmed, probable, and non-AFM, 227 (98%), 26 (100%), and 113 (98%), respectively, were hospitalized, including 127 (60%), 12 (57%), and 54 (50%), respectively, admitted to an intensive care unit; 27% (62) of those with confirmed AFM required respiratory support, 87% of whom (53/61) required mechanical ventilation. No deaths were reported during the acute illness of patients with confirmed AFM who had limb weakness onset in 2018; however, there were two reports of patients confirmed with AFM in 2018 who had died months after limb weakness onset.

Figure 1.

Confirmed cases of acute flaccid myelitis reported to CDC (N = 559) — United States, August 1, 2014–December 31, 2018

Figure 2.

Cases of acute flaccid myelitis reported to CDC, by case classification status — United States, 2018

Among patients with confirmed AFM, the interval between limb weakness onset to hospitalization (1 day) and to MRI (2 days) suggests early recognition by clinicians. Among patients with probable AFM, the interval from onset of limb weakness to hospitalization (3 days) and MRI (4 days) was significantly longer than that among those with confirmed AFM. Compared with patients with confirmed AFM, the interval from onset of limb weakness to hospitalization among patients with non-AFM (1 day) was similar, but the interval to MRI (3 days) was significantly longer (p = 0.002). Among patients with confirmed AFM, the median interval from onset of limb weakness to specimen collection ranged from 2–7 days, depending on specimen type. The median interval from onset of limb weakness until reporting to CDC ranged from 18–36 days, with confirmed and probable cases reported earlier than non-AFM cases (Table 1).

Among all 233 patients with confirmed AFM, CSF, respiratory specimens, and stool specimens were tested from 74 (32%), 123 (53%), and 100 (43%) patients, respectively (Table 2). The highest positive yield (44%) was from respiratory specimens, of which EV-D68 was most commonly detected; only two (3%) CSF specimens tested positive (one each for EV-D68 and EV-A71). Testing of specimens from probable and non-AFM cases also identified multiple EV/RV types. Stool specimens from all patients with available specimens tested negative for poliovirus. Among specimens sent from 31 patients (17 confirmed, three probable, and 11 noncases) for arboviral testing, all were negative.

Among patients with confirmed AFM in 2018, the median interval between antecedent illness (e.g., febrile, respiratory, and/or gastrointestinal) during the preceding 4 weeks and onset of limb weakness (5 days), between limb weakness and hospitalization (1 day) and CSF collection (2 days) was similar to that in the 2016 outbreak, (5 days, 1 day, and 3 days, respectively) (Supplementary table, However, the median interval from onset of limb weakness to MRI, respiratory specimen collection, and stool collection was shorter in 2018 than in 2016 (2 days versus 3 days, 3 days versus 4.5 days, and 7 days versus 7.5 days, respectively). Reporting to CDC occurred at a median of 18 days (range = 0–208 days) in 2018 versus 15 days (range = 0–344 days) in 2016 for patients with confirmed AFM.