A rapid test at Tam Anh Hanoi General Hospital confirmed the child had flu B and elevated liver enzymes. His creatine kinase (CK) muscle enzyme level soared to 5,570 U/L, significantly higher than the normal range of 39-308 U/L, indicating severe muscle cell damage.

Doctor Nguyen Thi Phuong Thao, deputy head of the Pediatrics Department, stated that acute myositis is a rare complication of the flu, typically appearing as respiratory symptoms subside. The flu virus damages muscle fibers, causing pain in a child's thighs or calves. When muscles are damaged, CK muscle enzymes increase in the blood. Some cases also show increased AST and ALT liver enzyme levels. Without timely treatment, muscle cells are destroyed, releasing myoglobin protein, potassium, phosphorus, and other substances into the bloodstream, which risks electrolyte imbalance and metabolic acidosis.

Long received intravenous fluids to protect kidney function and increase the elimination of myoglobin protein through the kidneys. During treatment, Long's heart rate slowed to about 60 beats per minute (the normal range is approximately 70-100 beats/minute). Doctors ordered an electrocardiogram to assess heart function and rule out the risk of myocarditis.

Concurrently, Long received treatment for respiratory symptoms, electrolyte replenishment, and reduction of elevated liver enzymes. After four days of treatment, the child was fever-free, muscle pain had subsided, he ate well, and his CK levels were safe, leading to discharge. Children should avoid strong leg massages and limit physical activity for one week to prevent further damage to muscle fibers.

Doctor Thao examining Long before his discharge. *Photo: Hai Au*

Flu B is an acute respiratory infection caused by influenza type B virus, which typically circulates seasonally and spreads through the respiratory tract. Most patients experience symptoms such as fever, cough, sore throat, runny nose, and body aches, and can recover within 5-7 days with appropriate care.

According to Doctor Thao, many still believe flu B is milder than flu A, often leading to complacency in monitoring and treatment. However, the flu B virus can still cause various complications, such as pneumonia and encephalitis, especially in children, the elderly, or individuals with underlying health conditions.

Doctor Thao advises that when children have fever or pain, parents should only use fever-reducing medication containing paracetamol at the correct dosage of 10-15 mg/kg body weight, administered every 4-6 hours. It is crucial not to use aspirin for children with viral infections due to the high risk of Reye's syndrome, a rare condition that causes liver and brain damage and can be life-threatening. Parents should not administer antibiotics without a doctor's prescription, as antibiotics are ineffective against the flu virus.

Sick children should be isolated in their own rooms and use separate personal items. If a child exhibits unusual signs such as severe muscle pain, especially in both legs, muscle weakness, difficulty walking, or dark urine, families must take the child to the hospital for examination.

Trinh Mai