Definition/General
Introduction:
Viral respiratory infections are the most common cause of acute respiratory illness worldwide
They affect both upper and lower respiratory tract
Sputum cytology provides rapid diagnosis in severe cases
Cytopathological changes are characteristic for different viral agents.
Origin:
Viral respiratory infections result from direct viral invasion of respiratory epithelium
Common viruses include influenza A and B
Parainfluenza viruses
Respiratory syncytial virus (RSV)
Adenovirus
Human metapneumovirus
Rhinovirus
Coronavirus.
Classification:
Classified by viral family and clinical syndrome
RNA viruses: Influenza, parainfluenza, RSV, rhinovirus, coronavirus
DNA viruses: Adenovirus, herpes simplex virus
Enveloped vs non-enveloped viruses
Seasonal patterns vary by virus type.
Epidemiology:
Peak incidence during winter months
Influenza causes annual epidemics
RSV common in infants and elderly
Adenovirus causes year-round infections
Increased severity in immunocompromised patients
Higher morbidity in extremes of age.
Clinical Features
Presentation:
Acute onset respiratory symptoms
Fever and constitutional symptoms
Cough (initially dry, later productive)
Dyspnea in severe cases
Myalgia and headache
Sore throat
Nasal congestion.
Symptoms:
Dry cough progressing to productive
Clear to purulent sputum
Chest tightness
Shortness of breath
Fatigue
Low-grade to high fever
Chills and rigors.
Risk Factors:
Immunocompromised state
Chronic lung diseases
Elderly patients
Young children
Cardiovascular disease
Diabetes mellitus
Healthcare workers
Close contact exposure.
Screening:
Clinical suspicion during viral seasons
Rapid viral testing
PCR-based detection
Cytological examination
Chest imaging
Serial monitoring in severe cases.
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Gross Description
Appearance:
Clear to white sputum initially
May become yellow-green with secondary infection
Scant volume in early stages
Increased viscosity
May be blood-tinged in severe cases.
Characteristics:
Mucoid consistency
Non-purulent initially
Frothy appearance possible
Minimal odor
Progressive volume increase
Color changes with disease progression.
Size Location:
Variable sputum volume
Upper respiratory tract primarily affected
Lower respiratory tract involvement in severe cases
Bilateral disease common
Diffuse involvement.
Multifocality:
Multiple viral strains possible
Mixed viral-bacterial infections
Progressive respiratory involvement
Systemic manifestations
Secondary complications.
Microscopic Description
Histological Features:
Viral inclusion bodies characteristic feature
Nuclear inclusions (DNA viruses)
Cytoplasmic inclusions (RNA viruses)
Multinucleated giant cells
Epithelial cell changes
Inflammatory cell infiltrate.
Cellular Characteristics:
Influenza: Epithelial necrosis with viral inclusions
Adenovirus: Intranuclear inclusions (smudge cells)
RSV: Multinucleated syncytial cells
Parainfluenza: Cytoplasmic inclusions
HSV: Ground glass nuclei with Cowdry A inclusions.
Architectural Patterns:
Epithelial desquamation
Cellular swelling and ballooning
Loss of cilia
Squamous metaplasia
Inflammatory exudate
Reactive epithelial changes.
Grading Criteria:
Severity based on extent of epithelial damage
Mild: Focal epithelial changes
Moderate: Widespread epithelial involvement
Severe: Extensive necrosis and inflammation
Viral load assessment.
Immunohistochemistry
Positive Markers:
Viral-specific antigens
Influenza A/B antigens
RSV antigen
Adenovirus antigen
Parainfluenza antigen
CMV antigen (immunocompromised)
Pan-viral markers.
Negative Markers:
Bacterial antigens absent
Fungal stains negative
Mycobacterial stains negative
Malignancy markers negative
Normal bacterial flora reduced.
Diagnostic Utility:
Essential for viral identification
Rapid diagnosis
Differentiates from other pathogens
Guides antiviral therapy
Infection control measures
Epidemiological tracking.
Molecular Subtypes:
Influenza A subtypes (H1N1, H3N2)
Influenza B lineages
RSV groups A and B
Adenovirus serotypes
Parainfluenza types 1-4
Coronavirus strains.
Molecular/Genetic
Genetic Mutations:
Viral genetic variations
Antigenic drift (influenza)
Antigenic shift (pandemic strains)
Host genetic factors
Immune response genes
Viral resistance mutations.
Molecular Markers:
Viral RNA/DNA detection
Real-time PCR
Viral sequencing
Neuraminidase inhibitor resistance
Viral load quantification
Host response markers.
Prognostic Significance:
Viral type determines severity
Viral load correlates with disease severity
Host immune status
Early detection improves outcomes
Antiviral resistance affects treatment
Coinfections worsen prognosis.
Therapeutic Targets:
Neuraminidase inhibitors (influenza)
RNA polymerase inhibitors
Viral entry inhibitors
Immune modulators
Combination therapy
Prophylactic measures.
Differential Diagnosis
Similar Entities:
Bacterial pneumonia (different cellular pattern)
Atypical pneumonia (Mycoplasma, Chlamydia)
Fungal infections (different morphology)
Non-infectious causes (drug-induced, aspiration)
Malignancy (atypical cells).
Distinguishing Features:
Viral: Viral inclusions present
Viral: Specific antigen positivity
Bacterial: Neutrophilic exudate
Bacterial: Gram stain positive
Fungal: PAS/GMS positive
Atypical: Mixed inflammatory pattern
Malignancy: Cytological atypia.
Diagnostic Challenges:
Distinguishing viral from bacterial pneumonia
Mixed infections
Secondary bacterial infection
Non-specific inflammatory changes
Specimen quality issues
Timing of collection.
Rare Variants:
SARS-CoV-2 (COVID-19)
MERS-CoV
Hantavirus
Human bocavirus
Enterovirus D68
Avian influenza
Swine influenza.
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], adequate for evaluation
Diagnosis
Viral respiratory infection - [viral type suspected]
Viral Inclusions
[Inclusion type] identified in [cell type] showing [characteristics]
Microscopic Findings
Shows [epithelial changes] with [viral cytopathic effects]
Epithelial Changes
Epithelial changes: [desquamation/necrosis/reactive changes]
Inflammatory Response
Inflammatory response: [lymphocytic/mixed/minimal]
Special Studies
Viral antigens: [test performed]: [positive/negative]
PCR testing: [recommended/pending/results]
Viral culture: [recommended/results]
Clinical Correlation
Clinical correlation with [acute symptoms] and [seasonal pattern]
Final Diagnosis
Sputum cytology: Viral respiratory infection - [virus type]