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Incidence, Risk Factors and Outcomes Among Children With Acute Flaccid Myelitis

A Population-based Cohort Study in a California Health Network Between 2011 and 2016

Kane, Miranda S. DO, MPH*; Sonne, Chris MD†,‡; Zhu, Shiyun MPH§; Malhotra, Amit MD; Van Haren, Keith MD; Messacar, Kevin MD**; Glaser, Carol A. DVM, MPVM, MD††

The Pediatric Infectious Disease Journal: July 2019 - Volume 38 - Issue 7 - p 667–672
doi: 10.1097/INF.0000000000002276
Original Studies

Background: Acute flaccid myelitis (AFM) is defined as an acute onset of limb weakness with longitudinal spinal gray matter lesions. Reporting bias and misdiagnosis confound epidemiologic studies of AFM. We mitigated these confounders by using a large data set to assess AFM incidence, risk factors and outcomes in a fixed population.

Methods: A retrospective cohort study was conducted within Kaiser Permanente Northern California population among children 1–18 years. Cases met radiographic and clinical criteria for AFM and were confirmed by two clinicians. Clinical and demographic data were assessed.

Results: A total of 28 patients met study criteria for AFM between January 1, 2011 and December 31, 2016, an overall rate of 1.46 per 100,000 person-years. Incidence increased from 0.30 to 1.43 cases/per 100,000 person-years between 2011 and 2016, respectively. Median age was 9 years. Risk factors included male sex, Asian ancestry and history of asthma, atopic dermatitis or head injury. Risk factors associated with poliomyelitis were absent. Prodromal illness was common; enterovirus was the most common pathogen detected (n = 5). Among the 27 patients with 12-month follow-up, most demonstrated some improvement, 11 (41.0%) had full recovery, but several had significant deficits with one death reported after the study period.

Conclusions: We employed a closed-population study to generate AFM incidence, risk and outcome data. Our findings support previous reports of male sex and atopy as risk factors. Interval increase in incidence, predisposing Asian ancestry and history of head injury were unique findings to this study. Overall prognosis was better than prior reports, but recovery was incomplete in several patients.

From the *Department of Pediatric Hospital Medicine, Kaiser Permanente Oakland Medical Center, Oakland, California, University of California Berkeley School of Public Health, Berkeley, California

Department of Radiology, Kaiser Permanente Oakland Medical Center, Oakland, California

Department of Radiology, University of California San Francisco, San Francisco, California

§Division of Research, Biostatistical Consulting Unit, Kaiser Permanente, Oakland, California

Department of Pediatric Specialty, Kaiser Permanente Oakland Medical Center, Oakland, California

Department of Neurology, Stanford University School of Medicine, Palo Alto, California

**Department of Pediatrics, Sections of Hospital Medicine and Infectious Diseases, University of Colorado/Children’s Hospital Colorado, Aurora, Colorado

††Department of Pediatric Infectious Diseases, Kaiser Permanente Oakland Medical Center, Oakland, California.

Accepted for publication December 13, 2018.

The authors have no funding or conflicts of interest to disclose.

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s website (

Address for correspondence: Miranda S. Kane, DO, MPH, Department of Pediatric Hospital Medicine, Kaiser Permanente Oakland Medical Center, University of California Berkeley School of Public Health, 3600 Broadway Ave, Oakland, California. E-mail:;

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