Classification of ARI

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Classification of Acute Respiratory Infections (ARI)

Acute respiratory infections (ARI) may cause inflammation of the respiratory tract anywhere from the nose to the alveoli, with a wide range of combinations of symptoms and signs. They are among the most common human ailments and a major cause of morbidity and mortality, especially in young children and the elderly.

I. Classification by Site of Infection

ARI is primarily classified based on the anatomical site of infection into:

A. Acute Upper Respiratory Tract Infections (AURI)

Infections occurring above the vocal cords include:

Condition	Key Features
Common cold (rhinitis)	Rhinorrhea, nasal congestion, mild fever
Pharyngitis	Sore throat; streptococcal (Group A Strep) or viral
Otitis media	Ear pain; peak at ~5 years of age
Sinusitis	Facial pain, purulent discharge
Laryngitis	Hoarseness, dysphonia
Epiglottitis	Life-threatening; stridor, drooling (mainly H. influenzae type b)

B. Acute Lower Respiratory Tract Infections (ALRI)

Infections occurring below the vocal cords include:

Condition	Key Features
Laryngotracheitis (Croup)	Barking cough, inspiratory stridor
Bronchitis	Productive cough, no consolidation
Bronchiolitis	Mainly in infants; RSV is the most common cause
Pneumonia	Consolidation, fast breathing, chest indrawing

II. WHO Clinical Classification (for Children 2 months to 5 years)

The WHO/IMCI (Integrated Management of Childhood Illness) program classifies ARI in children into four clinical categories based on severity, guiding treatment decisions:

Category I: Very Severe Disease

Danger signs:

Not able to drink
Convulsions or abnormally sleepy/difficult to wake
Stridor in a calm child
Severe malnutrition

Management: Refer URGENTLY to hospital; give first dose of antibiotic; treat fever and wheezing if present.

Category II: Severe Pneumonia

Key signs:

Chest indrawing (lower chest wall draws in during inspiration)
May also have nasal flaring, grunting, cyanosis

Management: Urgent hospital referral; antibiotic; treat fever and wheezing.

Category III: Pneumonia (Not Severe)

Key signs:

Fast breathing (≥50/min if child aged 2-12 months; ≥40/min if 12 months to 5 years)
No chest indrawing

Management: Home care; oral antibiotic; reassess in 2 days.

Category IV: No Pneumonia - Cough or Cold

Signs:

No danger signs, no chest indrawing, no fast breathing
Simple upper respiratory symptoms

Management: No antibiotics needed (mostly viral); supportive home care; refer if cough >30 days (consider TB, asthma, whooping cough).

III. Classification for Young Infants (< 2 months)

Young infants are classified separately because they become sick rapidly, may not cough with pneumonia, and often show only nonspecific signs (poor feeding, fever/hypothermia):

Classification	Signs
Severe bacterial infection	Fast breathing (≥60/min), severe chest indrawing, fever/hypothermia, convulsions, not feeding well
Local bacterial infection	Skin pustules, umbilical infection, eye discharge
No severe disease	None of the above

IV. Classification by Etiology

Viral (most common - majority of ARIs)

Rhinovirus, Influenza (A, B), Parainfluenza (1-4), RSV, Adenovirus, Coronavirus (including SARS-CoV-2), Metapneumovirus

Bacterial

Streptococcus pneumoniae (most common bacterial cause of pneumonia)
Haemophilus influenzae type b (second most common pneumonia; epiglottitis)
Streptococcus pyogenes (Group A) - pharyngitis
Mycoplasma pneumoniae - atypical pneumonia
Bordetella pertussis - whooping cough
Staphylococcus aureus - severe pneumonia in infants

V. Classification by Severity (General)

Severity	Features
Mild	Simple cold, rhinitis, mild pharyngitis - self-limiting
Moderate	Sinusitis, AOM, non-severe pneumonia - antibiotic may be needed
Severe	Severe pneumonia, epiglottitis, severe bronchiolitis - hospitalization required
Very severe	Respiratory failure, sepsis, ARDS - ICU level care

Key Points on Antibiotic Use

Per Harrison's (22nd ed.), the only common ARIs that should be treated with antibiotics are:

Acute otitis media (AOM)
Sinusitis (meeting criteria)
Streptococcal pharyngitis
Pneumonia

The overwhelming majority of ARIs are viral and self-limited; antibiotics are inappropriate for most cases.

Sources:

Park's Textbook of Preventive and Social Medicine (WHO/IMCI ARI classification)
Harrison's Principles of Internal Medicine, 22nd Edition (URI/LRI classification, antibiotic stewardship)

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