What are the management criteria for influenza-like illness (ILI)?

Management of Influenza-like Illness (ILI)

The management of influenza-like illness requires a structured approach based on symptom severity, with antiviral therapy recommended within 48 hours of symptom onset for patients with fever >38°C and respiratory symptoms, and antibiotics reserved only for those with evidence of bacterial complications or high-risk status. 1, 2

Definition and Diagnosis

• ILI is characterized by fever (>38°C) plus at least one respiratory symptom (cough or sore throat) 2, 3
• Only about 51% of hospitalized patients with confirmed influenza meet the CDC criteria for ILI, suggesting a high index of suspicion is needed in hospital settings 4
• The most common symptoms of ILI include cough (90%) and fever (66%), while sore throat is less common (21%) 4
• Laboratory testing is recommended for hospitalized patients and those where confirmation would change management decisions 5

Initial Assessment and Risk Stratification

• Assess vital signs including temperature, respiratory rate, pulse, blood pressure, mental status, and oxygen saturation 1, 2

• Consider hospital admission if the patient has two or more unstable clinical factors 1:

  • Temperature >37.8°C
  • Heart rate >100/min
  • Respiratory rate >24/min
  • Systolic blood pressure <90 mmHg
  • Oxygen saturation <90%
  • Inability to maintain oral intake
  • Abnormal mental status

• For children, additional indicators for hospital admission include 1:

  • Signs of respiratory distress (markedly raised respiratory rate, grunting, intercostal recession)
  • Cyanosis
  • Severe dehydration
  • Altered conscious level
  • Complicated or prolonged seizure

Antiviral Treatment

• Antiviral therapy (neuraminidase inhibitors) is recommended if all of the following criteria are met 1, 5:

  • Acute influenza-like illness
  • Fever (>38°C)
  • Symptomatic for two days or less

• Standard adult dosing: Oseltamivir 75 mg twice daily for five days (reduce dose by 50% if creatinine clearance <30 ml/min) 1, 5, 6

• Special considerations for antiviral therapy 1, 5:

  • Immunocompromised or elderly patients may still be eligible despite lack of documented fever
  • Hospitalized patients who are severely ill may benefit from antiviral treatment started >48 hours from disease onset
  • Oseltamivir reduces illness duration by approximately 24 hours and may reduce hospitalization rates 5, 6

Antibiotic Management

• Previously well adults with acute bronchitis complicating influenza, without pneumonia, do not routinely require antibiotics 1, 2

• Consider antibiotics in the following scenarios 1:

  • Previously well adults who develop worsening symptoms (recrudescent fever or increasing dyspnea)
  • Patients at high risk of complications with lower respiratory features
  • Patients with confirmed or suspected bacterial pneumonia

• For non-severe influenza-related pneumonia 1:

  • Most patients can be adequately treated with oral antibiotics
  • Preferred oral options: co-amoxiclav or a tetracycline (e.g., doxycycline)
  • When oral therapy is contraindicated, use intravenous co-amoxiclav or a second/third generation cephalosporin with a macrolide

Supportive Care

• Provide oxygen therapy for hypoxic patients with monitoring of oxygen saturations 1, 2:

  • Aim to maintain PaO2 >8 kPa and SaO2 ≥92%
  • High concentrations of oxygen can safely be given in uncomplicated pneumonia
  • For patients with pre-existing COPD and ventilatory failure, guide oxygen therapy with repeated arterial blood gas measurements

• Non-invasive ventilation considerations 1:

  • May be helpful in patients with COPD and ventilatory failure
  • May serve as a bridge to invasive ventilation when level 3 beds are in high demand
  • Should be used in respiratory/critical care units experienced in infection control measures

• Assess for cardiac complications, volume depletion, and need for intravenous fluids 1

• Provide nutritional support in severe or prolonged illness 1

Monitoring and Follow-up

• Monitor vital signs at least twice daily, more frequently in severe cases 1

• Consider using an Early Warning Score system for convenient monitoring 1

• Prior to discharge, review patients for clinical stability 1:

  • Patients should remain hospitalized if they have two or more unstable clinical factors
  • Follow-up clinical review should be arranged for patients with significant complications or worsening of underlying disease

Special Considerations for Children

• Management approach varies by symptom severity 1:

  • Mild cases (coughs and mild fevers): home treatment with antipyretics and fluids
  • High fever (>38.5°C) with cough or ILI symptoms: seek advice from healthcare professional
  • Children at increased risk (chronic conditions, breathing difficulties, severe earache, prolonged vomiting, drowsiness): should be seen by a physician and offered antibiotics plus oseltamivir (if >1 year of age)

• Laboratory investigations for hospitalized children 1:

  • Complete blood count with differential
  • Urea, creatinine, electrolytes, liver enzymes
  • Blood culture
  • Chest X-ray for hypoxic or severely ill children
  • Pulse oximetry

Common Pitfalls to Avoid

• Relying solely on the classic ILI definition may miss cases, as only about half of hospitalized patients with confirmed influenza meet the standard criteria 4
• Delaying antiviral treatment beyond 48 hours significantly reduces effectiveness 5, 6
• Unnecessary antibiotic use in uncomplicated cases without evidence of bacterial infection 1
• Inadequate monitoring of oxygen saturation and respiratory status 1
• Failure to consider other viral etiologies, as rhinovirus and other pathogens can cause similar presentations, especially during influenza season 7