Explain about urti and lrti
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Upper Respiratory Tract Infections (URTI) and Lower Respiratory Tract Infections (LRTI)
Anatomy: Where the Line Is Drawn
The respiratory tract is divided at the vocal cords (larynx):
- Upper respiratory tract: nose, nasopharynx, oropharynx, laryngopharynx, larynx
- Lower respiratory tract: trachea, bronchi, bronchioles, alveolar space
URIs occur above the vocal cords; LRIs occur below them. In practice, etiology and symptoms overlap considerably - influenza, for example, can span both.
- Harrison's Principles of Internal Medicine 22E, p. 296
URTI - Upper Respiratory Tract Infections
Definition
Acute infections occurring above the vocal cords. URIs - including nonspecific URI (common cold), otitis media, sinusitis, and pharyngitis - are collectively the most common symptomatic reason for seeking medical care in the United States.
- Harrison's Principles of Internal Medicine 22E
Epidemiology
- Average adult: 2-4 URIs per year
- Children: 6-10 URIs per year
Common URTI Conditions
| Condition | Key Features |
|---|---|
| Common Cold (Rhinitis) | Rhinorrhea, nasal congestion, mild sore throat, low-grade fever - mostly viral |
| Pharyngitis / Tonsillitis | Erythematous, swollen, often purulent oropharynx; significant throat pain; lymphadenopathy. Bacterial or viral etiology. |
| Sinusitis (Rhinosinusitis) | Often follows a viral URTI; defined by symptoms persisting >10 days or worsening after 5 days |
| Otitis Media (AOM) | Polymicrobial; one-third of children with viral URTI develop AOM |
| Epiglottitis | Associated with Haemophilus influenzae; infection of soft tissue near vocal cords - potentially life-threatening airway obstruction; largely eliminated in vaccinated populations |
| Peritonsillar Abscess | Complication of tonsillitis; occurs in children >5 years |
- Tietz Textbook of Laboratory Medicine, 7th Edition
- Scott-Brown's Otorhinolaryngology Head & Neck Surgery
Etiology
- Viral: Rhinovirus (most common cold), coronavirus, RSV, parainfluenza, adenovirus, influenza, EBV
- Bacterial: Group A Streptococcus (pharyngitis), H. influenzae, Moraxella catarrhalis, Streptococcus pneumoniae (sinusitis, AOM)
Clinical Features
- Runny nose, nasal congestion, sneezing
- Sore throat, odynophagia
- Low-grade fever (high fever suggests bacterial or influenza)
- Hoarseness, cough (laryngitis)
- Ear pain/pressure (otitis media)
Serious Complications (if untreated or severe)
- Meningitis
- Brain abscess
- Bacteremia
- Otitis media
- Peritonsillar / retropharyngeal abscess
- Airway obstruction (epiglottitis)
- Tietz Textbook of Laboratory Medicine, 7th Edition
Diagnosis
- Primarily clinical
- Throat swab for Rapid Antigen Test or culture (Group A Strep)
- Flocked swabs with liquid Amies medium for bacterial cultures
- Molecular/PCR panels for viral pathogens
Treatment
- Viral URIs: Symptomatic only - saline irrigation, decongestants, antipyretics (acetaminophen or ibuprofen - not aspirin in children due to Reye's syndrome risk)
- Bacterial (Group A Strep pharyngitis): Penicillin / amoxicillin; macrolides if penicillin-allergic
- Sinusitis (if bacterial): Amoxicillin-clavulanate
- AOM: Amoxicillin first-line
- Antibiotics are NOT indicated for the vast majority of viral URIs. At least half of ambulatory antibiotic prescriptions for acute respiratory infections are inappropriate.
- Harrison's Principles of Internal Medicine 22E
URTI and Anesthesia (Important Clinical Note)
URTI is the most common non-preventable cause of surgery cancellations. Infection-induced inflammation of the upper respiratory mucosa results in airway hyperreactivity, increasing anesthetic risk.
- Campbell Walsh Wein Urology
LRTI - Lower Respiratory Tract Infections
Definition
Infections occurring below the larynx, involving the trachea, bronchi, bronchioles, and lung parenchyma (alveoli).
Common LRTI Conditions
| Condition | Key Features |
|---|---|
| Acute Bronchitis | Inflammation of the tracheobronchial tree; barking/croupy cough, fever, sputum production; mostly viral |
| Chronic Bronchitis | Heavy mucus production; cough with sputum for ≥3 months over 2 years; associated with COPD |
| Pneumonia (CAP) | Inflammation of lung parenchyma; productive/nonproductive cough, fever, chills, dyspnea |
| Hospital-Acquired Pneumonia (HAP) | Onset >48 hours after hospital admission |
| Ventilator-Associated Pneumonia (VAP) | Affects nearly 30% of ICU patients; up to 300,000 cases/year in the US |
| Bronchiolitis | Primarily viral (RSV); mainly in infants/young children |
- Tietz Textbook of Laboratory Medicine, 7th Edition
- Quick Compendium of Clinical Pathology, 5th edition
Etiology
Community-Acquired Pneumonia (CAP):
- Most common overall: Streptococcus pneumoniae
- Typical pneumonia (abrupt onset, lobar infiltrate): S. pneumoniae, S. aureus, H. influenzae
- Atypical pneumonia (dry cough, patchy infiltrates): Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella
- Viral CAP: Influenza, RSV, parainfluenza, rhinovirus, adenovirus, metapneumovirus, coronavirus
Host-Specific Pathogens:
| Risk Factor | Pathogens |
|---|---|
| COPD | H. influenzae, M. catarrhalis, Legionella |
| Alcoholism | S. pneumoniae, Klebsiella, anaerobes |
| Neutropenia | Gram-negative aerobic bacilli |
| Cystic fibrosis / Bronchiectasis | Pseudomonas aeruginosa, Burkholderia cepacia, S. aureus |
| Bird exposure | Chlamydophila psittaci, Cryptococcus |
| HAP/VAP | MRSA, E. coli, Klebsiella, Pseudomonas, Serratia, fungi |
- Quick Compendium of Clinical Pathology, 5th edition
Clinical Features
- Cough (productive or dry, depending on type)
- Fever and chills (often high-grade in bacterial pneumonia)
- Dyspnea / shortness of breath
- Pleuritic chest pain (if pleural involvement)
- Fever is typically absent or low-grade in bronchitis - high-grade or persistent fever suggests pneumonia
Diagnosis
- Chest X-ray: Lobar consolidation (typical), patchy/bilateral infiltrates (atypical/viral)
- Sputum Gram stain and culture: Quality assessed first - specimens with abundant epithelial cells are rejected
- Bronchoalveolar lavage (BAL): Gold standard for ICU/VAP patients
- Blood cultures: For severe/hospitalized pneumonia
- CBC: Leukocytosis
- Urinary antigen tests: For Legionella and S. pneumoniae
Treatment
| Type | Treatment |
|---|---|
| Viral bronchitis | Supportive; antibiotics not indicated |
| CAP (outpatient, mild) | Amoxicillin OR doxycycline / macrolide (if atypical suspected) |
| CAP (hospitalized) | Beta-lactam + macrolide, or respiratory fluoroquinolone |
| CAP (ICU/severe) | Beta-lactam + macrolide or beta-lactam + fluoroquinolone |
| HAP / VAP | Broad-spectrum agents covering MRSA and Pseudomonas |
| Bronchiolitis (RSV, children) | Supportive (nebulized saline, oxygen); palivizumab prophylaxis in high-risk infants |
URTI vs. LRTI at a Glance
| Feature | URTI | LRTI |
|---|---|---|
| Anatomical site | Above vocal cords | Below vocal cords |
| Common conditions | Common cold, pharyngitis, sinusitis, AOM, epiglottitis | Pneumonia, bronchitis, bronchiolitis |
| Typical pathogens | Rhinovirus, Group A Strep, H. influenzae | S. pneumoniae, Mycoplasma, Influenza, RSV |
| Fever | Low-grade usually | Often high-grade (bacterial pneumonia) |
| Cough | Mild, dry | Prominent, may be productive |
| Dyspnea | Absent (except epiglottitis) | Common in pneumonia |
| CXR | Normal | Infiltrates, consolidation in pneumonia |
| Antibiotics needed | Rarely (only bacterial strep, AOM, sinusitis) | Often yes (for bacterial pneumonia) |
| Severity | Usually mild, self-limited | Can be life-threatening (VAP, severe CAP) |
| Complications | Meningitis, abscess, AOM | Empyema, respiratory failure, sepsis |
Prevention
- Hand hygiene (the single most effective measure)
- Physical distancing; face masks during outbreaks
- Vaccination: Influenza (annual), S. pneumoniae, H. influenzae type B, COVID-19
- Isolation of ill individuals
- Smoking cessation (reduces COPD-related LRTI risk)
Harrison's Principles of Internal Medicine 22E; Tietz Textbook of Laboratory Medicine, 7th Edition; Quick Compendium of Clinical Pathology, 5th edition
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