Respiratory tract infections (RTIs)

Respiratory tract infections are among the most common causes of illness globally, involving infectious processes in the airways and lungs. They can be classified into upper respiratory tract infections (URTIs) and lower respiratory tract infections (LRTIs) based on the anatomical site of infection.

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1. Upper Respiratory Tract Infections (URTIs)

Includes the common cold, sinusitis, pharyngitis, tonsillitis, laryngitis, and otitis media.

Causes

• Viral: Rhinovirus, influenza virus, coronavirus, adenovirus.

• Bacterial: Streptococcus pyogenes, Haemophilus influenzae, Moraxella catarrhalis.

Treatment
Most viral URTIs are self-limiting and require only symptomatic management. Antibiotics are reserved for confirmed or strongly suspected bacterial infections.

• Common Cold:

  • No specific antiviral therapy for most cases.

  • Symptomatic relief: Paracetamol (acetaminophen) 500–1000 mg orally every 4–6 hours (max 4 g/day) for fever/pain; Ibuprofen 200–400 mg orally every 6–8 hours (max 1200 mg/day OTC).

• Acute Bacterial Sinusitis:

  • First-line: Amoxicillin-clavulanate 875 mg/125 mg orally twice daily for 5–7 days (adults).

  • Alternative (penicillin allergy): Doxycycline 100 mg orally twice daily for 5–7 days.

• Streptococcal Pharyngitis (Group A Streptococcus):

  • First-line: Penicillin V 500 mg orally twice daily for 10 days or 250 mg orally four times daily for 10 days.

  • Alternative: Azithromycin 500 mg orally on day 1, then 250 mg once daily for days 2–5.

• Acute Otitis Media (Adults):

  • First-line: Amoxicillin 875 mg orally twice daily for 5–7 days.

  • Alternative: Cefuroxime 500 mg orally twice daily for 5–7 days.

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2. Lower Respiratory Tract Infections (LRTIs)

Includes acute bronchitis, bronchiolitis, and pneumonia.

Causes

• Viral: Influenza, RSV, SARS-CoV-2.

• Bacterial: Streptococcus pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae, Chlamydophila pneumoniae.

Treatment

• Acute Bronchitis:

  • Usually viral — antibiotics not indicated unless bacterial cause suspected.

  • Symptomatic: Paracetamol 500–1000 mg orally every 4–6 hours as needed, maximum 4 g/day; Dextromethorphan 10–20 mg orally every 4 hours or 30 mg every 6–8 hours (max 120 mg/day) for dry cough.

• Community-Acquired Pneumonia (Mild–Moderate, Outpatient):

  • First-line (healthy adults): Amoxicillin 1 g orally three times daily for 5 days.

  • Alternative (penicillin allergy): Doxycycline 100 mg orally twice daily for 5 days or Azithromycin 500 mg orally on day 1, then 250 mg daily for 4 days.

  • In patients with comorbidities: Amoxicillin-clavulanate 875 mg/125 mg orally twice daily + Azithromycin 500 mg on day 1, then 250 mg daily for 4 days; or Levofloxacin 750 mg orally once daily for 5 days.

• Severe Community-Acquired Pneumonia (Hospitalized):

  • Ceftriaxone 1–2 g IV once daily + Azithromycin 500 mg IV or orally once daily.

  • Alternative: Levofloxacin 750 mg IV or orally once daily.

• Bronchiolitis (primarily in infants; in adults, supportive care):

  • Supportive management — oxygen therapy, hydration; no routine antibiotics unless bacterial coinfection suspected.

• Influenza (within 48 hours of symptom onset):

  • Oseltamivir 75 mg orally twice daily for 5 days (adults).

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3. Tuberculosis (Pulmonary)

Caused by Mycobacterium tuberculosis.

• First-line regimen (intensive phase): Isoniazid 5 mg/kg/day (max 300 mg) + Rifampicin 10 mg/kg/day (max 600 mg) + Pyrazinamide 20–25 mg/kg/day + Ethambutol 15–20 mg/kg/day for 2 months, followed by continuation phase with Isoniazid + Rifampicin for 4 months.

Quick-Reference Chart – RTIs (Adults)

Infection Type	Common Pathogens	First-Line Treatment (Generic)	Adult Dose & Duration	Alternative (if allergy/resistance)	Adult Dose & Duration
Common Cold (Viral rhinitis)	Rhinovirus, Coronavirus, Adenovirus	Symptomatic only: Paracetamol (Acetaminophen)	500–1000 mg PO q4–6h, max 4 g/day	Ibuprofen	200–400 mg PO q6–8h, max 1200 mg/day OTC
Acute Bacterial Sinusitis	S. pneumoniae, H. influenzae, M. catarrhalis	Amoxicillin-Clavulanate	875/125 mg PO BID × 5–7 days	Doxycycline	100 mg PO BID × 5–7 days
Streptococcal Pharyngitis	S. pyogenes	Penicillin V	500 mg PO BID × 10 days OR 250 mg PO QID × 10 days	Azithromycin	500 mg PO day 1, then 250 mg PO daily × 4 days
Acute Otitis Media	S. pneumoniae, H. influenzae, M. catarrhalis	Amoxicillin	875 mg PO BID × 5–7 days	Cefuroxime	500 mg PO BID × 5–7 days
Acute Bronchitis (Bacterial suspected)	Mycoplasma pneumoniae, B. pertussis	Azithromycin	500 mg PO day 1, then 250 mg PO daily × 4 days	Doxycycline	100 mg PO BID × 5–7 days
Community-Acquired Pneumonia (Healthy outpatient)	S. pneumoniae, M. pneumoniae, C. pneumoniae	Amoxicillin	1 g PO TID × 5 days	Doxycycline OR Azithromycin	Doxy: 100 mg PO BID × 5 days; Azithro: 500 mg PO day 1, then 250 mg daily × 4 days
Community-Acquired Pneumonia (Comorbidities)	Same as above + Gram-negatives	Amoxicillin-Clavulanate + Azithromycin	875/125 mg PO BID × 5 days + Azithro regimen above	Levofloxacin	750 mg PO daily × 5 days
Severe CAP (Hospitalized)	S. pneumoniae, H. influenzae, atypicals	Ceftriaxone + Azithromycin	Ceftriaxone: 1–2 g IV daily + Azithro: 500 mg IV/PO daily	Levofloxacin	750 mg IV/PO daily
Influenza (Within 48 h onset)	Influenza A/B	Oseltamivir	75 mg PO BID × 5 days	Zanamivir (inhaled)	10 mg inhaled BID × 5 days
Tuberculosis (Pulmonary)	M. tuberculosis	Isoniazid + Rifampicin + Pyrazinamide + Ethambutol (2 mo), then INH + RIF (4 mo)	INH: 5 mg/kg (max 300 mg), RIF: 10 mg/kg (max 600 mg), PZA: 20–25 mg/kg, EMB: 15–20 mg/kg daily	As per national TB guidelines for resistance	Dose varies by regimen