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Pediatric influenza

OVERVIEW

What is pediatric influenza?

Pediatric influenza, also known as the flu in children, is an acute respiratory infectious disease caused by infection with the influenza virus[1]. Influenza viruses can be classified into four types: influenza A, B, C, and D, corresponding to type A, B, C, and D influenza[2].

Typical symptoms of pediatric influenza include sudden fever (body temperature exceeding 37.2°C)[3], headache, muscle pain, general fatigue, and discomfort, accompanied by cold-like symptoms such as cough, sore throat, nasal congestion, and runny nose.

Influenza is characterized by a rapid onset, strong contagiousness, rapid spread, and a tendency to cause epidemics or pandemics[4]. Compared to healthy adults over 18 years old, infants and young children are more likely to develop severe cases, so parents should take it seriously.

For children under 5 years old, especially those under 2, or those with high-risk complications (such as obesity, asthma, epilepsy, or tumors), antiviral treatment with medications like oseltamivir should be initiated as early as possible after diagnosis. Most cases recover after treatment, but a few may develop complications such as otitis media, pneumonia, or encephalitis, which can be fatal in severe cases.

Is influenza the same as the common cold?

No, they are different in the following ways:

  1. Different pathogens: Pathogens are microorganisms that cause illness. Influenza is specifically caused by the influenza virus, while the common cold is mostly caused by rhinoviruses, but can also be triggered by coronaviruses, parainfluenza viruses, respiratory syncytial viruses, etc.
  2. Different symptoms: The common cold mainly affects the nose, causing symptoms like nasal congestion, runny nose, and sneezing, with milder fever, fatigue, and body aches. It usually resolves within a week. In contrast, influenza has milder nasal symptoms but more pronounced fever (often 39–40°C), fatigue, headache, and body aches. Some patients may also experience abdominal pain, bloating, or vomiting, and severe cases can lead to respiratory failure or death.
  3. Different contagiousness: Influenza is more contagious and affects people of all ages. Therefore, once diagnosed with influenza, isolation is recommended, and students should take leave from school.

SYMPTOMS

What are the symptoms when a child gets the flu?

  1. Most people infected with the influenza virus have an incubation period of 1–7 days (usually 1–4 days, averaging 2 days), during which there are no noticeable symptoms.
  2. Then, a sudden onset of high fever (body temperature 39.1–41°C) occurs, accompanied by chills, shivering, headache, body aches, fatigue, loss of appetite, and other symptoms. There may also be sore throat, dry cough, nasal congestion, runny nose, chest discomfort, facial flushing, and conjunctival congestion. A small number of cases may experience nausea, vomiting, or diarrhea. The clinical symptoms of influenza in infants and young children are often atypical[5].
  3. If infected with influenza B virus, more pronounced symptoms such as nausea, vomiting, diarrhea, and poor appetite may occur.
  4. If there are no complications, fever usually subsides gradually after 3–4 days of illness, and recovery takes about a week, with systemic symptoms improving. However, symptoms like coughing may take 1–2 weeks to fully resolve. Weakness and fatigue in children may persist for several weeks, sometimes referred to as "post-flu weakness."

What complications may occur in children with the flu?

Children under 5 years old (especially those under 2) are more prone to complications, severe cases, or even death, so sufficient attention is required. Possible complications include:

  1. Pneumonia: Symptoms may include cough, chest pain, sputum production, fever, and difficulty breathing. Severe cases may lead to significant lung dysfunction, such as hypoxia. Persistent or recurrent fever and cough after the primary illness subsides may indicate secondary bacterial pneumonia[4].
  2. Otitis media: Symptoms include ear pain, fever, and hearing abnormalities.
  3. Heart damage: Such as myocarditis, pericarditis, or even heart failure, which may manifest as palpitations, chest tightness, fever, wheezing, or edema.
  4. Neurological damage: Such as encephalitis, meningitis, or myelitis, which may present as headache, nausea, fever, neck stiffness, confusion, numbness in limbs, or paralysis.
  5. Myositis: Characterized by significant muscle pain, most commonly in the legs.

Once complications arise, it indicates a more severe case of influenza, requiring prompt medical attention and active treatment.

What symptoms in a child suggest a potentially severe condition?

  1. Persistent high fever for more than 3 days, accompanied by severe cough, purulent or bloody sputum, or chest pain.
  2. Rapid breathing, difficulty breathing, or cyanosis (bluish lips).
  3. Altered mental state, such as lethargy, restlessness, seizures, or confusion.
  4. Severe vomiting, diarrhea, dehydration, dizziness, numbness in hands and feet, or fainting.

Immediate medical attention is required if any of these symptoms occur.

During which seasons are children more susceptible to the flu?

Autumn and winter are peak seasons for influenza, with most cases occurring between November and March. This seasonal pattern is referred to as "seasonal influenza."

In northern China, influenza typically peaks in winter and spring, while southern China experiences two peaks—winter/spring and summer. The intensity of outbreaks varies by region and year. For detailed local flu trends, consult the local Centers for Disease Control and Prevention (CDC).

Children who recover from one flu infection may still contract another type or subtype of influenza in the same season. Therefore, even after vaccination or previous infection, isolation and cross-infection prevention measures should not be neglected.

CAUSES

What causes influenza in children?

The cause of influenza is infection with the influenza virus. The influenza virus is highly contagious and easily spreads among people. Both adults and children are susceptible to influenza virus infection.

What is the influenza virus?

The full name of the influenza virus is "influenza virus," an RNA virus that can be divided into four types: A, B, C, and D. Currently, the main strains infecting humans are H1N1 and H3N2 subtypes of influenza A virus, as well as the Victoria and Yamagata lineages of influenza B virus[1].

Is influenza contagious?

Yes, influenza is a highly contagious disease that spreads rapidly. After entering the human population, the influenza virus primarily spreads through droplets and is highly infectious. Its antigens are also prone to mutation, making airborne transmission more widespread and likely to cause epidemics[6].

How is the influenza virus transmitted?

  1. Droplet transmission: When influenza patients or asymptomatic carriers sneeze or cough, they release droplets containing the influenza virus into the air. Healthy individuals may become infected if their mucous membranes (eyes, nose, or mouth) come into contact with these droplets.
  2. Indirect contact transmission: Droplets containing the influenza virus can adhere to objects (such as doorknobs, handrails, tables, or chairs). If a healthy person touches these objects and then touches their mucous membranes (mouth, nose, or eyes), they may also become infected.
  3. Aerosol transmission: In specific settings (such as crowded and poorly ventilated rooms), the influenza virus may also spread through aerosols. Aerosols refer to all solid and liquid particles suspended in a gas (such as air). When droplets mix with air, they form aerosols, which can cause infection when inhaled[1].

How long is an influenza patient contagious?

The peak viral shedding for influenza A occurs 24–48 hours after the onset of illness and then declines rapidly. After 5–10 days of illness, little to no viral replication can be detected in the respiratory tract. Influenza B virus shedding appears to follow a bimodal pattern, peaking 48 hours before symptoms appear and again 24–48 hours after symptoms appear. This means patients are contagious both before and after symptoms develop. Immunocompromised hosts and children (especially first-time infections) may shed the virus for several weeks due to their relatively weaker immunity.

In short, influenza patients and asymptomatic carriers are the main sources of infection. They are contagious from the late incubation period through the acute phase. The virus is typically shed in respiratory secretions for 3–7 days, but children, immunocompromised individuals, and critically ill patients may shed the virus for over a week[1].

During this time, it is best not to let children attend school while sick to avoid infecting others. However, if they remain fever-free (temperature ≤ 37.2°C[3]) for more than 24 hours without using fever-reducing medications (such as ibuprofen), their contagiousness is significantly reduced, and they can resume normal activities.

How can the influenza virus be killed?

The influenza virus is heat-sensitive and can be inactivated by heating at 100°C for 1 minute or at 56°C for 30 minutes.

The virus is also sensitive to acids, ether, ultraviolet light, and common disinfectants such as ethanol, iodophor, iodine tincture, peracetic acid, and 84 disinfectant. Therefore, these disinfectants can be used for sterilization. Ultraviolet irradiation or direct sunlight exposure can also disinfect contaminated surfaces[6].

DIAGNOSIS

When should children with flu seek medical attention promptly?

In flu-endemic areas, children under 5 years old (especially infants under 2 years old) with typical clinical symptoms such as chills, fever (temperature exceeding 37.2°C), headache, and fatigue should be suspected of having the flu and seek medical attention promptly[4].

Older children (5 years and above) should also seek immediate medical care if they experience persistent high fever, severe cough, rapid breathing, difficulty breathing, lethargy, drowsiness, or confusion.

How do doctors diagnose pediatric flu?

Doctors diagnose flu based on the current flu epidemic situation, the patient's symptoms, physical examination, and pathogen test results. Chest X-rays may reveal lung infections[1].

A sudden increase in similar cases with mild respiratory symptoms (cough, sputum, difficulty breathing) but severe systemic symptoms (high fever ≥39°C, chills, headache) combined with seasonal epidemiological data can strongly suggest flu.

During flu season, even with atypical symptoms, flu should be prioritized for high-risk groups like children, and treatment should start early. Confirmation requires pathogen testing (e.g., nasal/throat swabs, nucleic acid tests) or serological blood tests at fever clinics[1,6].

What are the clinical criteria for suspected flu?

During flu season or outbreaks (consult local CDC or doctors), consider flu infection and initiate antiviral treatment for high-risk groups if:

  1. Children with fever (>37.2°C) and acute respiratory symptoms (cold, bronchitis, laryngitis, flu-like illness);
  2. Children with fever (>37.2°C) and underlying chronic lung diseases (pneumonia, asthma).

Diagnosing pediatric flu is challenging, especially in infants. Fever with respiratory symptoms (cough, sore throat) plus close contact with a confirmed flu case within 7 days warrants high suspicion and prompt medical care[5].

Other viruses (e.g., RSV, parainfluenza) may cause similar flu-like symptoms during flu season. However, distinguishing flu from other viruses isn't always necessary, as supportive treatments are similar[6].

What are the pathogen tests for flu?

Pathogen tests detect the influenza virus in respiratory secretions (nasal/throat swabs, sputum) or blood. Common methods include:

  1. Viral antigen tests: Fast but low sensitivity (~50% positive rate). A positive result supports diagnosis, but negative doesn't rule out flu[1].
  2. Nucleic acid tests: Highly accurate, detects virus types (A/B/C/D), ideal for early diagnosis[1].
  3. Viral culture: The gold standard but time-consuming, making it impractical for rapid diagnosis[1].
  4. Serological tests: Detect antibodies. A 4-fold rise in IgG during recovery confirms flu but isn't useful for early diagnosis[1].

What other tests might be needed for suspected flu in children?

Mild cases may not require lab confirmation and can be diagnosed empirically based on symptoms (fever >37.2°C, chills, cough, etc.).

Testing is recommended for high-risk children or those with complications (pneumonia, myocarditis, otitis media). Severe cases may need arterial blood gas, cardiac enzymes, ECG, CSF analysis, chest X-ray/CT, or brain CT/MRI to assess complications. Consult a doctor for specifics.

TREATMENT

Which department should I visit for pediatric flu?

Children with a temperature above 37.2°C can go to the fever clinic; those who fall ill at night can visit the emergency department; those with severe cough and phlegm can go to the respiratory or infectious disease outpatient clinic.

How is pediatric flu treated?

All flu cases require antiviral treatment. The earlier the antiviral treatment begins, the better. Based on flu epidemiological history and clinical laboratory results, suspected influenza viral pneumonia should be treated with antivirals without waiting for pathogen confirmation[7].

  1. Antiviral treatment: Children under 5 years old (especially under 2) or high-risk groups for complications (e.g., obesity, asthma, epilepsy, tumors) should start antiviral treatment as early as possible (within 48 hours of flu-like symptoms) to alleviate symptoms, reduce complications, and shorten the course of illness, without waiting for pathogen test results. Even if the rapid flu test is negative, antiviral treatment should still be administered.
  2. Symptomatic treatment: For fever, headache, or severe body aches, antipyretic and analgesic treatment can be given. Common pediatric medications include acetaminophen or ibuprofen. Aspirin, aspirin-containing drugs, or other salicylate preparations are prohibited. For high fever (temperature above 39°C), physical cooling (using ice packs or cold compresses for no more than 30 minutes) and antipyretics can be applied. Children with severe cough and phlegm should be given antitussive and expectorant medications. Oxygen therapy may be considered for children with hypoxia symptoms[1].
  3. Complication treatment: For those with complications, doctors will provide targeted treatments, such as respiratory support (ventilator assistance), antibiotics, or measures to promote sputum expulsion (e.g., frequent position changes and back patting).

Who is at high risk for flu complications?

  1. Children under 5, especially under 2, are more prone to severe complications;
  2. Adults aged ≥ 65;
  3. Patients with chronic respiratory, cardiovascular (excluding hypertension), kidney, liver, hematologic, neurological, or neuromuscular diseases (e.g., epilepsy, cerebral palsy), metabolic/endocrine disorders, malignancies, or immunosuppression;
  4. Obese individuals (BMI > 30, calculated as weight (kg) ÷ height² (m));
  5. Pregnant women[1].

What antiviral drugs can be used for pediatric flu?

Currently approved antiviral drugs for children in China include:

  1. Oseltamivir (capsules/granules): 5-day course (longer for severe cases). Dosage varies by age and weight.
    • For treatment and prevention in children ≥1 year; neonates >14 days only for treatment.
    • Optimal administration is within 48 hours of symptom onset, but efficacy remains if given within 96 hours[5].
  2. Zanamivir (inhalation spray): For children ≥7 years. Side effects are rare (mostly nasal symptoms) but may trigger bronchospasm; use cautiously in children with asthma[5].
  3. Peramivir (injection): 1–5 days (longer for severe cases).
  4. Baloxavir marboxil: For children ≥5 years. Dosage is weight-based—follow medical advice strictly.

Is antiviral treatment still necessary after 48 hours of symptoms?

Yes.

While antivirals work best within 48 hours, severe cases can still benefit from treatment beyond this window[5].

Do children with flu need antibiotics?

No. Since flu is viral, antibiotics are ineffective. Unnecessary use causes side effects and antibiotic resistance. However, if bacterial co-infection occurs (e.g., persistent fever, yellow phlegm, pus discharge), antibiotics may be prescribed after confirmation.

How long does pediatric flu take to recover? Is hospitalization needed?

Uncomplicated flu is self-limiting, with fever subsiding in 3–4 days and recovery in ~1 week (cough and fatigue may linger). Most cases require rest, hydration, and antipyretics (e.g., ibuprofen; avoid aspirin in under-18s[1]). Severe cases or complications may prolong recovery and require hospitalization.

DIET & LIFESTYLE

What should I pay attention to if there is a child with flu at home?

  1. Isolate at home and do not go to school. When the child can remain fever-free for more than 24 hours without using antipyretics, it indicates lower contagiousness, and they may resume activities.
  2. If the child cooperates, they can wear a mask during the contagious phase.
  3. Teach the child cough etiquette—cover their mouth and nose with a tissue when coughing or sneezing.
  4. Both the child and other family members should wash hands frequently using soap or hand sanitizer.
  5. Ventilate the room regularly by opening windows.
  6. Maintain appropriate indoor temperature and humidity.
  7. The child should get plenty of rest and drink more fluids.
  8. Provide easily digestible but nutritious meals, including fresh fruits. Avoid skipping meals, as it hinders recovery.
  9. Monitor body temperature and symptoms. Seek medical attention promptly if severe symptoms mentioned earlier occur.

PREVENTION

Can the flu be prevented? How to prevent it?

The flu can be prevented. Prevention methods include:

  1. Get vaccinated against the flu every year.
  2. Wash hands frequently with soap or hand sanitizer.
  3. Keep windows open for ventilation.
  4. Avoid contact with diagnosed flu patients. If a family member has the flu, the patient should wear a mask, and personal items like towels and cups should be stored separately and disinfected promptly.
  5. During flu outbreaks, avoid public places and poorly ventilated areas.
  6. Avoid putting hands in the mouth, picking the nose, or rubbing the eyes after washing hands.
  7. Clean and disinfect toys regularly.

Everyone should get vaccinated, especially high-risk groups and those living in nursing homes[4].

When is the best time to get a flu vaccine?

The best time to get vaccinated is 1–2 months before the peak of the flu season, which for most people in China is between September and November[4]. This ensures antibody levels remain high during the winter flu season. However, vaccination is still recommended even if the optimal timing is missed.

Can flu be prevented with medication besides vaccines?

Yes. Vaccination is the preferred method, but antiviral drugs are also effective[4]. However, medication should not replace vaccination. Prevention with drugs can be divided into pre-exposure and post-exposure prophylaxis (recommended after a doctor's risk assessment).

  1. Pre-exposure prophylaxis: When there are confirmed flu cases in a child's community, kindergarten, or school, the following children should consider antiviral prevention: unvaccinated children under 5 or high-risk individuals (e.g., with obesity, asthma, epilepsy, or cancer); children under 5 vaccinated less than 2 weeks prior (before full immunity develops); and older children with chronic conditions (e.g., asthma, congenital heart disease, or diabetes). Antivirals can be stopped 2 weeks after vaccination. If unvaccinated, they may be used throughout the flu season[4].

  2. Post-exposure prophylaxis: Children under 5 or high-risk individuals who had close contact with a flu patient within 24 hours of symptom onset (or until fever resolves) may receive prophylaxis within 48 hours of exposure.

Common preventive medications include oseltamivir, zanamivir, laninamivir, and baloxavir marboxil—always use under medical supervision.

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