Definition/General
Introduction:
Bacterial respiratory infections are major causes of morbidity and mortality worldwide
They primarily affect the lower respiratory tract
Sputum cytology provides rapid diagnostic information
It guides empirical antibiotic therapy before culture results.
Origin:
Bacterial pneumonia results from aspiration of organisms from the oropharynx
Hematogenous spread from distant sites
Direct extension from adjacent infections
Common pathogens include Streptococcus pneumoniae
Haemophilus influenzae
Staphylococcus aureus
Klebsiella pneumoniae.
Classification:
Classified as community-acquired or hospital-acquired pneumonia
Typical bacteria: S
pneumoniae, H
influenzae, S
aureus
Atypical bacteria: Mycoplasma, Chlamydia, Legionella
Gram-positive vs Gram-negative organisms
Antibiotic-resistant strains.
Epidemiology:
Leading cause of infectious mortality
Peak incidence in winter months
Higher prevalence in developing countries
Elderly and immunocompromised at highest risk
Healthcare-associated infections increasing
Antibiotic resistance rising globally.
Clinical Features
Presentation:
Acute onset respiratory symptoms
High fever with chills and rigors
Productive cough with purulent sputum
Pleuritic chest pain
Dyspnea
Tachypnea and tachycardia
Constitutional symptoms.
Symptoms:
Purulent sputum production
Chest pain worse with breathing
Shortness of breath
High fever (>38.5°C)
Rigors and sweating
Malaise and fatigue
Decreased appetite.
Risk Factors:
Advanced age (>65 years)
Chronic lung diseases
Immunocompromised state
Smoking
Alcoholism
Diabetes mellitus
Heart failure
Recent hospitalization
Aspiration risk.
Screening:
Clinical assessment with CURB-65 score
Chest radiography
Sputum examination
Blood cultures
Arterial blood gases
Inflammatory markers (CRP, PCT).
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Gross Description
Appearance:
Purulent, thick sputum
Yellow-green coloration
Copious volume
May be blood-streaked
Rust-colored (pneumococcal)
Currant-jelly (Klebsiella)
Foul-smelling (anaerobes).
Characteristics:
Tenacious consistency
Mucopurulent nature
Offensive odor (anaerobic infection)
Homogeneous appearance
Increased viscosity
Color varies with organism.
Size Location:
Variable sputum volume (50-200 mL daily)
Lower respiratory tract origin
Lobar consolidation pattern
Bilateral involvement possible
Pleural involvement in severe cases.
Multifocality:
Single organism typically predominates
Mixed bacterial infections possible
Secondary bacterial invasion
Nosocomial superinfection
Drug-resistant organisms.
Microscopic Description
Histological Features:
Abundant neutrophils (>25 per low-power field)
Bacterial organisms visible
Purulent exudate
Alveolar filling
Epithelial cell sloughing
Macrophages with engulfed bacteria.
Cellular Characteristics:
Neutrophilic predominance
Degenerative changes in neutrophils
Bacteria within cells and extracellular
Gram-positive cocci (Streptococcus)
Gram-negative rods (Klebsiella, Pseudomonas)
Clusters of organisms.
Architectural Patterns:
Dense neutrophilic infiltrate
Alveolar space filling
Bronchial epithelial damage
Fibrin deposition
Vascular congestion
Inflammatory edema.
Grading Criteria:
Quality assessment by Bartlett's criteria
Grade 0: <10 epithelial cells, <25 neutrophils
Grade 1+: 10-25 epithelial cells
Grade 2+: adequate specimen
Grade 4+: many neutrophils, few epithelial cells.
Immunohistochemistry
Positive Markers:
Gram stain for bacterial identification
Neutrophil markers (MPO, elastase)
Bacterial antigens
Pneumococcal antigen
Legionella antigen
Inflammatory markers.
Negative Markers:
Viral inclusions absent
Fungal stains negative (unless coinfection)
Acid-fast stains negative
Malignancy markers negative
Atypical organisms absent.
Diagnostic Utility:
Essential for rapid bacterial identification
Gram stain morphology
Guides empirical antibiotic therapy
Quality assessment
Differentiates from other pathogens
Monitors treatment response.
Molecular Subtypes:
S
pneumoniae serotypes
MRSA vs MSSA
Extended-spectrum beta-lactamase (ESBL) producers
Carbapenem-resistant organisms
Multidrug-resistant (MDR) strains
Pandemic clones.
Molecular/Genetic
Genetic Mutations:
Antibiotic resistance genes
Beta-lactamase genes
Methicillin resistance (mecA)
Fluoroquinolone resistance
Vancomycin resistance
Carbapenemase genes.
Molecular Markers:
16S rRNA sequencing
Species-specific PCR
Resistance gene detection
Virulence factors
Molecular typing
Pneumococcal DNA.
Prognostic Significance:
Organism identification determines prognosis
Antibiotic susceptibility
Virulence factors
Host immune status
Early appropriate therapy improves outcomes
Resistance patterns affect treatment.
Therapeutic Targets:
Cell wall synthesis (beta-lactams)
Protein synthesis (aminoglycosides)
DNA replication (fluoroquinolones)
Folate synthesis (sulfonamides)
Combination therapy
Resistance circumvention.
Differential Diagnosis
Similar Entities:
Viral pneumonia (lymphocytic infiltrate)
Atypical pneumonia (mixed inflammatory pattern)
Fungal infections (different morphology)
Aspiration pneumonia (mixed organisms)
Pulmonary edema (no organisms).
Distinguishing Features:
Bacterial: Neutrophilic predominance
Bacterial: Visible organisms
Viral: Lymphocytic infiltrate
Atypical: Mixed inflammatory pattern
Fungal: Yeast/hyphal forms
Edema: No organisms or neutrophils.
Diagnostic Challenges:
Mixed infections
Prior antibiotic therapy
Poor specimen quality
Atypical presentations
Immunocompromised patients
Hospital-acquired infections.
Rare Variants:
Burkholderia cepacia (CF patients)
Stenotrophomonas maltophilia
Achromobacter xylosoxidans
Pandoraea species
Ralstonia pickettii
Emerging pathogens.
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
Sputum specimen, [volume] mL, [appearance], quality grade [1-4+]
Diagnosis
Bacterial respiratory infection - [organism morphology]
Gram Stain Results
Gram stain: [positive/negative] [cocci/rods] in [arrangement]
Microscopic Findings
Shows [neutrophil count] neutrophils with [bacterial description]
Cell Count Assessment
Neutrophils: [>25/hpf], Epithelial cells: [<10/hpf]
Organism Morphology
Organisms: [Gram reaction] [morphology] [arrangement]
Specimen Quality
Specimen quality: [Acceptable/Unacceptable] for culture
Culture Recommendation
Culture and sensitivity: [Recommended/Pending] for [organism]
Final Diagnosis
Sputum cytology: Bacterial respiratory infection