Flu Symptoms: Clinical Presentation and Management
Typical Clinical Presentation
Influenza presents with abrupt onset of high-grade fever (≥38°C in adults, ≥38.5°C in children), accompanied by systemic symptoms including myalgia, headache, malaise, and respiratory manifestations such as nonproductive cough, sore throat, and nasal discharge. 1, 2
Core Symptoms
- Fever with chills or sweats – hallmark feature with abrupt onset 3
- Cough – typically nonproductive initially 2, 4
- Myalgias and headache – prominent systemic symptoms 1
- Malaise and fatigue – patients often report feeling "sick" despite not appearing seriously ill 5
- Sore throat and rhinorrhea – common respiratory tract symptoms 2, 3
Age-Specific Presentations
- Children under 3-4 years may present atypically with fever, vomiting (>24 hours), drowsiness, severe earache, or breathing difficulties 1
- School-age children and teenagers typically present with classic symptoms and are key vectors for community spread 4
- Elderly patients may lack fever despite severe infection, particularly if immunocompromised 1
- Infants are at highest risk for hospitalization and may present with unexplained fever or laryngotracheobronchitis 4
Gastrointestinal Manifestations
- Abdominal pain, vomiting, and diarrhea occur in approximately 56% of patients, particularly with avian influenza strains 1
First-Line Management
Antiviral Treatment: Oseltamivir
Oseltamivir (Tamiflu) 75 mg twice daily for 5 days is the first-line antiviral treatment and should be initiated immediately in patients presenting within 48 hours of symptom onset, though high-risk and severely ill patients benefit even when started beyond this window. 1, 6
Indications for Immediate Treatment
- All hospitalized patients with suspected or confirmed influenza, regardless of timing or vaccination status 6, 7
- High-risk patients including:
- Children <2 years (especially infants <6 months) 6
- Adults ≥65 years 6
- Pregnant or postpartum women 6
- Immunocompromised patients (including those on long-term corticosteroids) 1, 6
- Chronic medical conditions: cardiac disease, COPD, asthma, diabetes, renal disease, liver disease, neurological disorders 1, 6
- Severely ill or progressively worsening patients, even if presenting >48 hours after onset 6, 7
Dosing Recommendations
Adults and adolescents ≥13 years: 75 mg orally twice daily for 5 days 1, 6
Pediatric weight-based dosing (twice daily for 5 days): 1, 6
- ≤15 kg: 30 mg
15-23 kg: 45 mg
23-40 kg: 60 mg
40 kg: 75 mg
Renal adjustment: Reduce dose by 50% (75 mg once daily) if creatinine clearance <30 mL/min 1, 7
Expected Clinical Benefits
- Reduces illness duration by 1-1.5 days when started within 48 hours 6, 7
- 50% reduction in pneumonia risk in patients with laboratory-confirmed influenza 6
- 34% reduction in otitis media in children 6
- Significant mortality benefit (OR 0.21) in hospitalized patients, even when started >48 hours after onset 6, 7
Common Adverse Effects
- Nausea and vomiting occur in approximately 10-15% of patients but are transient and rarely lead to discontinuation 1, 6
- Taking oseltamivir with food reduces gastrointestinal side effects 6
- No established link to neuropsychiatric events despite early reports 6
Critical Red-Flag Signs Requiring Hospital Referral
Adults
Patients with CRB-65 score ≥2 (particularly score 3+) or bilateral pneumonia on examination should be referred urgently for hospital assessment, regardless of CRB-65 score. 1
- Severe respiratory distress: markedly raised respiratory rate (>24/min), breathlessness with chest signs, oxygen saturation <90% 1
- Hemodynamic instability: systolic blood pressure <90 mmHg, hypotension 8
- Altered mental status or encephalopathy 1
- Recrudescent fever or worsening symptoms after initial improvement, particularly with increasing breathlessness 1, 8
- Inability to maintain oral intake 8
Children
Children with any of the following should be referred immediately for hospital assessment: 1
- Signs of respiratory distress: grunting, intercostal recession, markedly raised respiratory rate 1
- Cyanosis 1
- Severe dehydration 1
- Altered conscious level or complicated/prolonged seizures 1
- Signs of septicemia: extreme pallor, hypotension, floppy infant 1
- Persistent high fever despite 48 hours of treatment 8
Antibiotic Considerations
When Antibiotics Are NOT Routinely Required
Previously healthy patients with uncomplicated influenza (no pneumonia) do not require antibiotics. 1, 7
When to Add Antibiotics
Empiric antibiotics should be added immediately if bacterial superinfection is suspected, indicated by: 8, 7
- Persistent or worsening symptoms after 3+ days despite oseltamivir 8
- New or worsening productive cough with purulent sputum 8, 7
- Recrudescent fever or increasing breathlessness 1, 8
- Consolidation on chest imaging 7
- Patients with COPD or severe pre-existing illness 1
Antibiotic Regimens
Non-severe pneumonia (outpatient): 1, 7
- Co-amoxiclav 625 mg three times daily for 7 days, OR
- Doxycycline 200 mg loading dose, then 100 mg once daily for 7 days (if >12 years)
- Alternative: Clarithromycin or cefuroxime if penicillin-allergic
Severe pneumonia (hospitalized): 1, 7
- IV co-amoxiclav or cefuroxime/cefotaxime PLUS macrolide (clarithromycin/erythromycin)
These regimens cover common post-influenza bacterial pathogens: Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae 8, 7
Common Pitfalls to Avoid
Do NOT wait for laboratory confirmation before initiating oseltamivir in high-risk patients during influenza season – rapid tests have poor sensitivity, and delays reduce treatment effectiveness 6, 8
Do NOT withhold oseltamivir in high-risk or severely ill patients presenting >48 hours after symptom onset – mortality benefit persists when treatment is initiated up to 96 hours after illness begins 6, 7
Do NOT reflexively add antibiotics for viral influenza symptoms alone – this contributes to antibiotic resistance; add antibiotics only when bacterial superinfection is clinically suspected 7
Do NOT use oseltamivir as a substitute for annual influenza vaccination – vaccination remains the primary prevention strategy 6, 9
Diagnostic Approach
For most outpatients during influenza season with typical symptoms, clinical diagnosis is sufficient and laboratory confirmation is unnecessary. 3
When Laboratory Testing Is Useful
- Hospitalized patients with suspected influenza 3
- Patients where confirmed diagnosis will change treatment decisions 3
- Institutional outbreak settings for infection control 6
Preferred Diagnostic Tests
- Rapid molecular assays (RT-PCR, NAAT) are preferred – highly accurate, point-of-care, fast results 10, 3
- Rapid antigen tests have poor sensitivity; negative results should NOT exclude treatment in high-risk patients 6
Post-Exposure Prophylaxis
Oseltamivir 75 mg once daily for 10 days should be considered for high-risk household contacts exposed within 48 hours to a confirmed influenza case. 6, 9
Indications for Prophylaxis
- Severely immunocompromised patients (transplant recipients, chemotherapy patients) 6
- Unvaccinated high-risk individuals during community outbreaks 6
- Institutional outbreak control in nursing homes – all eligible residents for ≥2 weeks or until 1 week after outbreak ends 6
Pediatric Prophylaxis Dosing (once daily for 10 days)
- ≤15 kg: 30 mg
15-23 kg: 45 mg
23-40 kg: 60 mg
40 kg: 75 mg 6