Management of Influenza-like Illness (ILI)

Definition and Diagnosis

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, 3
Assess vital signs including temperature, respiratory rate, pulse, blood pressure, mental status, and oxygen saturation 1, 3
Laboratory testing is recommended for hospitalized patients and those where confirmation would change management decisions 4

Consider hospital admission if the patient has two or more unstable clinical factors, including 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, or abnormal mental status 1, 2, 5
For children, additional indicators for hospital admission include signs of respiratory distress, cyanosis, severe dehydration, altered conscious level, or complicated or prolonged seizure 5, 6

Antiviral therapy (neuraminidase inhibitors) is recommended if all of the following criteria are met: acute influenza-like illness, fever (>38°C), and symptomatic for two days or less 1, 2, 4
Standard adult dosing: Oseltamivir 75 mg twice daily for five days (reduce dose by 50% if creatinine clearance <30 ml/min) 1, 4
Oseltamivir reduces illness duration by approximately 24 hours and may reduce hospitalization rates 4

Previously well adults with acute bronchitis complicating influenza, without pneumonia, do not routinely require antibiotics 1, 2, 3
Consider antibiotics in the following scenarios: previously well adults who develop worsening symptoms, patients at high risk of complications with lower respiratory features, or patients with confirmed or suspected bacterial pneumonia 1, 2, 4

Provide oxygen therapy for hypoxic patients with monitoring of oxygen saturations, aiming to maintain PaO2 >8 kPa and SaO2 ≥92% 1, 5, 3
Non-invasive ventilation considerations: may be helpful in patients with COPD and ventilatory failure, and should be used in respiratory/critical care units experienced in infection control measures 1, 5, 7

Monitor vital signs at least twice daily, more frequently in severe cases 1, 2
Consider using an Early Warning Score system for convenient monitoring 1, 2
Prior to discharge, review patients for clinical stability, and follow-up clinical review should be arranged for patients with significant complications or worsening of underlying disease 1, 2, 3

Management approach varies by symptom severity: mild cases can be treated at home, while high fever or severe symptoms require medical attention 6, 4
Laboratory investigations for hospitalized children include complete blood count with differential, urea, creatinine, electrolytes, liver enzymes, blood culture, chest X-ray, and pulse oximetry 6, 4, 7, 5

The CRB-65 score is recommended for assessing the severity of influenza-related pneumonia, although it was originally developed for community-acquired pneumonia 8, 9
The CRB-65 score assigns points for confusion, respiratory rate, blood pressure, and age, with each criterion present contributing to the overall score 9, 10

A CRB-65 score of 0 indicates that a patient is likely suitable for home treatment 8
A CRB-65 score of 1 or 2 suggests considering hospital referral, particularly with a score of 2 10
Patients with bilateral chest signs on examination should be referred to hospital for further assessment regardless of CRB-65 score due to the rapid and fulminant course of primary viral pneumonia 8, 9, 10

Children should be referred for assessment if they exhibit shock 11
Children with recurrent apnea or slow irregular breathing should be considered for hospital referral 9

The CRB-65 score does not replace clinical judgment and social circumstances must be taken into account when making management decisions 8, 9, 10
There is no validated severity assessment tool developed specifically for influenza-related pneumonia, and the CRB-65 score is adapted from community-acquired pneumonia 9

Adults ≥65 years are at high risk for complications and mortality, accounting for >90% of influenza deaths 12, 13
Children <5 years, particularly infants <6 months, have a high hospitalization rate (~1,040/100,000) 14
The Centers for Disease Control and Prevention recommends antiviral therapy (oseltamivir 75mg twice daily for 5 days) for high-risk patients within 48 hours of symptom onset 15, 16, 17
Patients with underlying medical conditions, such as chronic respiratory disease, chronic heart disease, and immunosuppression, are at increased risk for complications and should receive antiviral therapy 15, 16, 17, 14

The American Academy of Pediatrics recommends oseltamivir dosing by weight for pediatric patients: <15 kg (<3 years): 30mg every 12 hours, 15-23 kg (<7 years): 45mg every 12 hours, >24 kg (>7 years): 75mg every 12 hours 16, 17, 18
Zanamivir is an alternative antiviral treatment, but should be avoided in patients with asthma or COPD due to bronchospasm risk 18

The Centers for Disease Control and Prevention recommends hospitalization for patients with severe illness, including those with CURB-65 scores ≥2, bilateral chest X-ray changes, or other high-risk features 15, 16, 17, 12
Pediatric patients should be transferred to the hospital if they show signs of respiratory distress, severe dehydration, or altered conscious level 16, 17, 12

Clinical diagnosis of influenza has limitations, with reported sensitivity of 63-78% and specificity of 55-71% compared with viral culture 12, 13
Treatment decisions should not be delayed for laboratory confirmation in high-risk patients 18

Oseltamivir reduces illness duration by 24-36 hours and risk of complications in high-risk patients, but current evidence does not definitively demonstrate mortality reduction 18