Marked Increase in Influenza-Associated Acute Myositis Among Children During the 2024-2025 Season: A Two-Season Retrospective Cohort Study From Riyadh, Saudi Arabia
Abstract
Background Influenza-associated acute myositis is well described in children, but most reports count cases without a denominator of infected children. How often influenza is followed by myositis, and whether that frequency shifts between seasons, therefore remains poorly defined. During the 2024-2025 season, pediatricians at our hospital saw an unusual number of children presenting with calf pain and inability to bear weight after laboratory-confirmed influenza. We compared the frequency of acute myositis among influenza-positive children across two matched seasons, and between influenza A and influenza B. Methodology We studied all unique children aged 0-14 years with influenza A or B confirmed by rapid antigen testing or polymerase chain reaction who presented to the pediatric emergency department of King Salman Hospital, Riyadh, between 1 November and 28 February of the 2023-2024 and 2024-2025 seasons, regardless of disposition. Each period spanned 120 matched days. Acute myositis required confirmed influenza in the same illness, acute calf or lower-limb pain, gait disturbance or inability to bear weight, creatine kinase above the laboratory upper reference limit of 308 U/L, and no documented alternative explanation. Analyses used risk ratios with 95% confidence intervals, chi-square tests, and a modified Poisson model with robust standard errors. Results The cohorts comprised 141 children in 2023-2024 and 173 in 2024-2025. Acute myositis occurred in 19 children (13.5%)…
How strong is the evidence?
Evidence Hub reads this as a cohort study, done in people. Its evidence level is 3 of 5 (Moderate · trial / cohort / secondary analysis). Trials without a large randomized design, cohorts and secondary analyses give moderate evidence. Reported size: 141 participants or records.
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