rhinorrhoea, sore throat, malaise commonly precede cough

Chest discomfort due to repeated coughing

Symptoms peak within 3–5 days and resolve in 1–3 weeks

Systemic toxicity absent or minimal

Normal daily activity usually preserved

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ACUTE BACTERIAL BRONCHITIS — Clinical Features

Persistent productive cough with thicker sputum

Symptoms last longer than typical viral illness

Fever and fatigue more pronounced

May follow untreated viral bronchitis

Increased airway inflammation causing chest heaviness

Risk of progression to pneumonia in elderly or children

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CHRONIC BRONCHITIS — Clinical Features

Chronic productive cough is dominant symptom

Morning sputum expectoration characteristic

Progressive exercise intolerance

Recurrent winter exacerbations

Associated with smoking or chronic pollutant exposure

Gradual development of airflow limitation

Frequent overlap with COPD spectrum

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MECHANICAL / IRRITANT BRONCHITIS — Clinical Features

Cough triggered by environmental exposure

Burning throat or chest irritation

Symptoms improve away from irritant source

Minimal systemic symptoms

Recurrent episodes related to occupational exposure

• Secondary bacterial infection may extend into alveoli.

• Persistent fever, worsening dyspnea → suspect pneumonia.

• Repeated acute inflammation damages bronchial mucosa.

• Mucus gland hypertrophy + chronic productive cough (>3 months/year).

• Post-infectious bronchial inflammation persists.

• Chronic cough or wheeze lasting weeks after infection.

• Viral bronchitis commonly triggers asthma attacks.

• Increased bronchospasm and reversible airflow obstruction.

• Major trigger in smokers and elderly.

• Increased sputum, dyspnea, hypoxia.

• Repeated infections weaken bronchial walls.

• Permanent airway dilation → recurrent infections.

• Especially in elderly or comorbid patients.

• Hypoxemia requiring oxygen support.

• Damaged mucosa favors bacterial persistence.

• Recurrent productive cough.

• Persistent systemic inflammation after viral illness.

• Prolonged weakness despite infection resolution.

• Fever higher, toxic appearance, pleuritic chest pain.

• Focal crepitations or bronchial breath sounds present.

• Chest X-ray shows consolidation → distinguishes from bronchitis.

• Episodic wheeze, chest tightness, triggers (allergen/exercise/cold air).

• Marked bronchodilator reversibility on spirometry.

• Often misdiagnosed as recurrent bronchitis.

• Occurs in smokers or elderly with chronic symptoms.

• Baseline dyspnea + chronic productive cough history.

• Spirometry shows persistent airflow obstruction.

• Predominantly nasal symptoms.

• Minimal chest findings.

• Cough mainly from post-nasal drip.

• Tachypnea, feeding difficulty, diffuse wheeze.

• Occurs mainly in infants.

• RSV and similar viruses common cause.

• Persistent paroxysmal cough >2 weeks.

• Inspiratory “whoop” or post-tussive vomiting.

• Often mistaken for prolonged bronchitis.

• Chronic cough, weight loss, night sweats.

• Hemoptysis or prolonged symptoms (>3 weeks).

• Requires imaging and microbiological confirmation.

• Chronic purulent sputum daily.

• Large volume sputum + recurrent infections.

• CT chest diagnostic.

• Dyspnea worse lying down, leg edema.

• Basal crackles + cardiomegaly on imaging.

• Pulmonary congestion mimics bronchitis cough.

• Sudden dyspnea, pleuritic chest pain, tachycardia.

• Disproportionate breathlessness compared to chest exam.

• Persistent cough in smoker.

• Weight loss, hemoptysis, non-resolving symptoms.

• Worse after meals or lying down.

• No infection signs; throat irritation common.

Bronchitis is caused by infectious agents or chronic airway irritation leading to inflammation of the bronchial mucosa.

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• Influenza virus

• Parainfluenza virus

• Respiratory Syncytial Virus (RSV)

• Human metapneumovirus

• Rhinovirus

• Coronavirus (including SARS-CoV-2)

• Adenovirus

• Streptococcus pneumoniae (Gram-positive cocci)

• Staphylococcus aureus (Gram-positive cocci)

• Haemophilus influenzae (Gram-negative coccobacillus)

• Moraxella catarrhalis (Gram-negative diplococcus)

• Mycoplasma pneumoniae

• Chlamydophila pneumoniae

• Bordetella pertussis

Bacterial bronchitis increasingly recognized in children and elderly patients.

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• Cigarette smoking (major cause)

• Biomass smoke exposure

• Air pollution / occupational dust

• Recurrent bacterial colonization of bronchi

• Untreated or recurrent respiratory infections

• Impaired mucociliary clearance

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• Age extremes (children & elderly)

• Reduced mucosal immunity

• Poor airway clearance

• Structural airway vulnerability

• Genetic mucus regulation factors (MUC5B involvement — emerging evidence)

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Clinical Reality (Important Teaching Point)

• Chronic cough with sputum mistaken as asthma

• Early inhaler/nebulizer use without infection control may worsen symptoms

• Mucus retention + airway irritation can aggravate bronchial inflammation

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Mechanistic Concept

Acute bronchitis → infection-driven inflammation

Chronic bronchitis → persistent injury + bacterial colonization + mucus dysregulation

ACUTE BRONCHITIS — Investigations

Acute bronchitis is primarily a clinical diagnosis

Most uncomplicated cases do not need lab tests—because results rarely change management.

Main reason to investigate is to exclude pneumonia or dangerous mimics

Investigations are indicated when there is high fever, tachypnea, hypoxia, pleuritic chest pain, focal crepitations, elderly/comorbid, or symptoms not improving.

Pulse oximetry is the fastest “danger screen”

Low SpO₂ suggests lower airway involvement beyond simple bronchitis → consider pneumonia, asthma/COPD exacerbation, bronchiolitis, heart failure.

Chest X-ray is NOT routine

Do CXR only if pneumonia is suspected

Clinical triggers: focal chest signs, high fever, RR ↑, hypoxia, significant weakness, immunocompromised, elderly.

CBC is optional and non-specific

Leukocytosis favors bacterial infection but is not reliable

Viral infection can also raise WBC mildly; normal WBC does not exclude bacterial infection.

CRP / Procalcitonin can help reduce unnecessary antibiotics

Low markers support viral/self-limited course

High procalcitonin supports bacterial lower respiratory infection (but interpretation must match clinical picture).

Sputum color is not a reliable test

Yellow/green sputum does not prove bacterial infection

It reflects neutrophils and inflammation, not necessarily bacteria.

Viral PCR is usually not required

Useful mainly during outbreaks or in high-risk patients (elderly, immunocompromised) where diagnosis affects isolation or antivirals (e.g., influenza/COVID).

Pertussis testing when cough pattern fits

If cough >2 weeks with paroxysms / inspiratory whoop / post-tussive vomiting → consider pertussis PCR/serology.

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ACUTE BACTERIAL BRONCHITIS / SUSPECTED SECONDARY BACTERIAL INFECTION — Investigations

Reason to investigate: identify treatable pathogen when course is atypical

Red flags: persistent fever, toxic appearance, worsening after initial improvement, high-risk patient.

Sputum Gram stain/culture is limited but helpful in selected cases

Useful in COPD/elderly, recurrent episodes, immunocompromised, or treatment failure

Not useful in routine mild bronchitis.

Blood cultures only if severe disease

Reserved for sepsis, severe pneumonia suspicion, or immunocompromised.

Consider atypical infection testing when clinical clue exists

Mycoplasma, Chlamydia pneumoniae → prolonged cough, community outbreaks, school clusters.

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CHRONIC BRONCHITIS / COPD-SPECTRUM — Investigations

Spirometry is the key investigation

Confirms airflow obstruction and distinguishes COPD phenotype from asthma

Chronic bronchitis is a clinical definition; COPD needs lung function proof.

Bronchodilator reversibility testing helps avoid asthma mislabeling

Marked reversibility suggests asthma component

Minimal reversibility supports COPD-spectrum chronic bronchitis.

Peak flow monitoring (home) helps pattern recognition

Large variability favors asthma

Stable low flow favors fixed obstruction.

Chest X-ray to look for alternative diagnosis or complications

Rules out: TB, bronchiectasis clues, malignancy, heart failure signs, pneumonia scars.

CT chest is not routine, but important when pattern is atypical

Indications: recurrent localized infections, hemoptysis, weight loss, suspicion of bronchiectasis, TB, tumor.

Sputum culture when frequent exacerbations or purulent sputum

To guide antibiotics and detect resistant organisms

Especially if repeated antibiotics already used.

ABG is for severity assessment

Indications: persistent hypoxia, cyanosis, confusion, severe COPD features.

Shows CO₂ retention / respiratory failure risk.

Eosinophil count can guide anti-inflammatory strategy in COPD

High blood eosinophils suggest steroid-responsive airway inflammation (useful in COPD overlap decisions).

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MECHANICAL / IRRITANT BRONCHITIS — Investigations

History is the investigation

Exposure type, timing, workplace trigger, indoor smoke.

Spirometry may show irritant-induced airway hyperreactivity

Can mimic asthma temporarily.

Chest X-ray only if severe exposure or symptoms persist

To rule out chemical pneumonitis.

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KEY CLINICAL REASONING SUMMARY

If cough + normal vitals + no focal chest signs → no tests needed

Treat as clinical acute bronchitis.

If fever/high RR/low SpO₂/focal crepts → do CXR to exclude pneumonia

If cough is recurrent for months → spirometry is essential

This is the common place where asthma vs chronic bronchitis vs COPD gets wrongly labeled.

Condition Imaging Pattern

Bronchitis Normal or bronchial wall thickening

Pneumonia Focal consolidation

Pulmonary edema Bilateral diffuse opacities

TB Cavitation / upper lobe infiltrates

Bronchiectasis Dilated bronchi on HRCT

The process mainly affects the bronchial mucosa (not alveoli), so gas-exchange failure is uncommon unless there is underlying lung disease.

I*nflammatory mediators sensitize airway receptors → dry, irritating cough early; later productive cough as mucus increases.*

If infection reaches alveoli → consolidation, hypoxia, pleuritic pain and focal crepitations—then it is no longer “simple bronchitis.”

Chronic/recurrent bronchitis reflects repeated epithelial injury + mucus gland hypertrophy

Repeated infections/irritants (smoke, biomass, pollution) → goblet cell hyperplasia, mucus gland enlargement, impaired clearance → persistent productive cough and recurrent infections.

Mucus biology influences susceptibility

Airway mucins (e.g., MUC5B) help trap pathogens; altered mucus properties + poor clearance can predispose to prolonged cough, mucus plugging, and recurrent lower respiratory infections.

Specimen Types

• Sputum sample

• Bronchial wash / bronchoalveolar lavage (BAL)

• Endobronchial biopsy (rarely required)

• Nasopharyngeal swab (viral cases)

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Microscopic Pathology Findings

Acute bronchitis

• Bronchial mucosal edema

• Epithelial desquamation

• Neutrophilic inflammatory infiltrate

• Increased mucus secretion

• Hyperemia of bronchial wall

Viral bronchitis

• Lymphocytic infiltration predominance

• Ciliary epithelial damage

• Minimal tissue destruction

Bacterial bronchitis

• Neutrophil-rich exudate

• Purulent mucus plugs

• Possible bacterial colonies

Chronic bronchitis

• Goblet cell hyperplasia

• Submucosal gland enlargement

• Thickened bronchial wall

• Chronic inflammatory infiltrate

• Mucus gland hypertrophy (↑ Reid index)

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Key Histological Marker

• Reid Index > 0.4 → suggests chronic bronchitis

(ratio of gland thickness to bronchial wall thickness)

{Autopsy (post-mortem lung specimens) — classical teaching source

Surgical lung specimens (lobectomy, pneumonectomy)

Rare bronchial biopsy research settings

NOT done in routine living patients}

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Microbiological Tests

• Gram stain of sputum

• Bacterial culture & sensitivity

• Viral PCR panel (Influenza, RSV, Parainfluenza, etc.)

• Atypical pathogen testing (Mycoplasma, Chlamydia)

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Inflammatory Laboratory Markers

• CBC → leukocytosis (bacterial)

• CRP / ESR elevation

• Procalcitonin (helps bacterial vs viral differentiation)

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When Pathology is NOT Needed

• Typical acute viral bronchitis → diagnosis is clinical

• Biopsy rarely indicated unless malignancy suspected

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Bronchitis — Pathology / Pathological Tests

Microscopic and Laboratory Examination of Respiratory Secretions

Sputum Gram Stain

• Rapid microscopic assessment of sputum

• Identifies:

• Gram-positive cocci (e.g., Streptococcus pneumoniae)

• Gram-negative organisms (e.g., Haemophilus influenzae, Klebsiella)

• Helps differentiate:

• Viral bronchitis (few bacteria)

• Bacterial bronchitis (predominant organism)

• Also evaluates specimen quality:

• ↑ neutrophils → true lower respiratory infection

• ↑ epithelial cells → saliva contamination

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Sputum Microscopy

• Neutrophilic inflammation → bacterial infection

• Lymphocyte predominance → viral infection

• Eosinophils → allergic / eosinophilic bronchitis

• Mucus plugs may be seen

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Sputum Culture & Sensitivity

• Confirms bacterial pathogen

• Guides antibiotic selection

• Especially useful in:

• Chronic bronchitis

• Recurrent infection

• Elderly or immunocompromised patients

• Treatment failure

Common isolates:

• Haemophilus influenzae

• Streptococcus pneumoniae

• Moraxella catarrhalis

• Gram-negative bacilli (advanced disease)

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Additional Pathological Evaluation (when indicated)

• Acid-fast bacilli stain → exclude pulmonary TB

• Fungal stain/culture → immunocompromised patients

• Cytology → exclude malignancy in chronic smokers

Prevention focuses on protecting bronchial mucosa and reducing airway inflammation

• Smoking cessation — most effective preventive measure for chronic bronchitis.

• Avoid passive smoke exposure (children and elderly highly vulnerable).

• Reduce exposure to air pollutants, dust, biomass fuel smoke, and occupational irritants.

• Use protective masks in polluted or industrial environments.

Infection prevention

• Hand hygiene reduces viral transmission.

• Avoid close contact during respiratory infections.

• Respiratory etiquette (mask during cough illness).

Vaccination

• Influenza vaccination reduces secondary bronchitis episodes.

• Pneumococcal vaccination in elderly and chronic lung disease patients.

Maintain airway health

• Adequate hydration maintains mucus viscosity.

• Regular physical activity improves mucociliary clearance.

• Balanced nutrition supports immune function.

Early treatment of upper respiratory infections

• Prevents spread of infection to lower airways.

Control predisposing conditions

• Manage allergic rhinitis, sinusitis, GERD.

• Control asthma or COPD overlap.

Environmental modification

• Improve indoor ventilation.

• Reduce indoor smoke from cooking fuels.

Childhood prevention

• Reduce exposure to tobacco smoke.

• Prevent recurrent viral infections through hygiene and nutrition.

Chest X-ray (CXR) — First-line imaging

• Often normal in acute bronchitis

• May show:

• Mild peribronchial thickening

• Increased bronchovascular markings

• Hyperinflation (especially in chronic smokers)

• No focal consolidation → helps differentiate from pneumonia

Clinical reasoning:

• Ordered when fever, hypoxia, elderly age, or severe symptoms present

• Used mainly to rule out pneumonia

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High-Resolution CT (HRCT Chest)

(Not routine — indicated in chronic or atypical cases)

Findings may include:

• Bronchial wall thickening

• Mucus plugging

• Air trapping (expiratory scans)

• Early bronchiectasis (if chronic disease progression)

• Small airway inflammation

Used when:

• Persistent cough >8 weeks

• Recurrent bronchitis

• Suspected ILD or bronchiectasis

• Unexplained dyspnea

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CT Chest (Contrast — selected cases)

Indications:

• Suspicion of malignancy

• Hemoptysis

• Non-resolving symptoms

• Complications (abscess, collapse)

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Ultrasound Lung (POCUS — emerging use)

• Usually normal in bronchitis

• Absence of consolidation supports non-pneumonic process

• Helpful bedside exclusion tool

Bronchitis is classified based on cause, duration, and pathological mechanism rather than microbial serotypes

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Duration-based classification

• Acute bronchitis — short-duration bronchial inflammation (<3 weeks), usually viral.

• Subacute bronchitis — persistent cough 3–8 weeks following infection.

• Chronic bronchitis — productive cough ≥3 months/year for ≥2 consecutive years (COPD spectrum).

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Etiology-based classification

• Acute viral bronchitis — most common; influenza, RSV, adenovirus, parainfluenza, coronavirus.

• Acute bacterial bronchitis — secondary infection; Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, atypical bacteria.

• Irritant / chemical bronchitis — smoke, pollutants, industrial gases, corrosive inhalation.

• Allergic bronchitis — hypersensitivity-mediated airway inflammation.

• Mechanical bronchitis — due to chronic aspiration, reflux, or airway irritation.

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Pathophysiology-based classification

• Inflammatory bronchitis — mucosal edema + cytokine-mediated inflammation.

• Hypersecretory bronchitis — mucus gland hypertrophy and excess secretion.

• Obstructive bronchitis — airway narrowing from edema, mucus plugging, bronchospasm.

• Infective–inflammatory bronchitis — combined infection and immune response.

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Clinical progression spectrum

• Upper respiratory infection → Acute bronchitis.

• Recurrent bronchitis → airway remodeling.

• Chronic bronchitis → COPD phenotype.

• Chronic inflammation → bronchiectasis (in susceptible individuals).

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Special clinical forms

• Smoker’s bronchitis.

• Childhood recurrent bronchitis.

• Post-viral bronchial hyperreactivity.

• Bronchitis associated with chronic lung disease (COPD/asthma overlap).

Due to transient bronchial mucosal edema, not fixed obstruction.

Normal oxygen saturation in most patients

Hypoxia uncommon unless severe infection or comorbidity.

No localized bronchial breathing

Absence of focal signs distinguishes from lobar infection.

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Moderate fever may occur

*Inflamed throat or tracheal tenderness

Chest findings still lack true consolidation*

If consolidation appears → consider pneumonia.

⸻

Diffuse rhonchi and wheeze on auscultation

Signs of airflow limitation

Peripheral edema in late stages

Suggests pulmonary hypertension or cor pulmonale.

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(smoke, pollution, chemical exposure)

Dry or irritative cough predominant

Minimal fever

Harsh breath sounds

Airway irritation signs without infection

Symptoms improve after removal of exposure

⸻

It can be

infection-> Viral/Bacterial/Fungal

Mechanical-> irritantants/corossives/pollution

Expectoration (sputum production) develops after initial phase

Throat irritation or burning sensation

Results from continuous coughing and upper airway inflammation.

Chest discomfort or heaviness

Due to bronchial inflammation and repeated cough effort rather than cardiac pain.

More common in viral bronchitis; high fever suggests alternative diagnosis (e.g., pneumonia).

Fatigue and malaise

Systemic inflammatory response during infection.

Shortness of breath (usually mild)

Occurs due to transient airway narrowing and mucus accumulation.

Especially in children, elderly, or patients with airway hyperreactivity; often misdiagnosed as asthma.

Hoarseness of voice

From associated laryngotracheal irritation.

• Most acute bronchitis is viral → supportive care is primary.

• Symptom relief is the primary goal in viral bronchitis.

Antipyretics & analgesics

• Short-term use for severe dry cough disturbing sleep.

• Avoid routine suppression when productive cough present.

• Cough helps airway clearance.

Expectorants / mucolytics

• Useful when sputum thick and difficult to expectorate.

• Improve mucus clearance.

Bronchodilators (conditional use)

• Only if bronchospasm or wheeze present.

• Not routine treatment for simple bronchitis.

• Indicated only when bacterial infection suspected:

• Persistent high fever

• Purulent sputum with toxicity

• Elderly/comorbid/immunocompromised patients

• Common targets: Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis.

Oxygen therapy

• Required in hypoxemia or COPD overlap.

• Misdiagnosis as asthma may worsen management strategy.

Management of underlying causes

• Treat GERD, sinusitis, or environmental exposure if contributing.