Children's hospitals are urging action as cases of rhabdomyolysis have recently increased among children recovering from influenza B.

The Korea Children's Hospital Association (KCHA) said on Monday that a survey of more than 120 member hospitals, conducted from December last year to March this year, identified 78 cases involving muscle pain, difficulty walking, and dark urine—symptoms caused by rhabdomyolysis. Most affected children were between the ages of 5 and 12.

In children, rhabdomyolysis is a viral infection that damages skeletal muscles, causing muscle cell contents to leak into the bloodstream. Sudden muscle pain, walking difficulties, and dark-colored urine during flu recovery should raise suspicions of the condition.

KCHA particularly warns that myoglobin, a muscle protein, can damage the kidneys, potentially leading to acute kidney failure—a serious complication requiring immediate medical attention.

“This year’s influenza B is generally considered mild, but unlike previous years, we are seeing a growing number of cases of viral rhabdomyolysis as a serious after-effect in some children,” said Choi Yong-jae, president of the KCHA.

“If detected early, rhabdomyolysis can be reversed with proper fluid therapy and electrolyte management. The best precaution is to have your child evaluated immediately if they experience unusual muscle pain or movement issues during flu recovery,” Choi said.

“With the recent rise in pediatric infectious diseases, the frequency of such cases is also increasing. We must remain vigilant and take proactive measures. Health authorities should closely monitor this trend, implement countermeasures, and establish a coordinated response system with pediatricians,” he added.