URTI

Upper Respiratory Tract Infections (URTIs)

• URTIs affect the nose, nasal passages, sinuses, ears, throat (pharynx and larynx)
• LRTIs affect the airways and lungs (trachea, bronchi, bronchioles, alveoli)
• Viral infections are the primary cause of URTIs
• Bacterial infections can also cause URTIs
• Common bacterial causes include Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus, Streptococcus pyogenes, Mycoplasma pneumoniae, RSV, Adenovirus, Influenza viruses

Anatomy and Natural Host Defenses

• The respiratory tract has natural defenses like saliva (pH, antibodies), sinuses (immunological defense), tonsils (lymphatic system), nose hairs (filtration), sneezing, cough reflex, cilia, mucosal layer (mucociliary escalator), and respiratory tract epithelium (antimicrobial peptides).
• Filtration of air occurs within the nasal passages, trapping large particles.
• Mucosal adherence and bacterial interference help maintain a healthy balance, preventing overgrowth.
• Stress can disrupt this balance, leading to infections like gram-negative pneumonias.

Common URTI Types and Their Characteristics:

• Croup: Primarily in children, caused by parainfluenza virus. Symptoms include barking cough, hoarseness, inspiratory stridor, and respiratory distress. Sometimes requires medical intervention (corticosteroids or nebulized epinephrine).
• Epiglottitis: Bacterial infection of epiglottis, often caused by Haemophilus influenzae type B (Hib) or Streptococcus pneumoniae. Symptoms include rapid onset of severe sore throat, high fever, difficulty swallowing, and drooling. Rapid progression to airway obstruction and respiratory failure is possible.
• Pertussis (Whooping Cough): Caused by Bordetella pertussis. Symptoms progress from a common cold to severe, uncontrollable coughing fits (paroxysmal cough) accompanied by a "whooping" sound. Potentially life-threatening, especially in infants and young children.
• Adenoiditis: Infection/inflammation of the adenoids, often viral or bacterial. Symptoms include nasal congestion, mouth breathing, snoring, and recurrent ear infections. Severe cases may require surgical intervention.
• Pharyngitis (Sore Throat): Viral (e.g., common cold, flu), or bacterial (e.g., strep throat). Symptoms include throat pain, difficulty swallowing, and swollen tonsils with or without white patches. Bacterial pharyngitis (strep throat) needs antibiotics to prevent complications.
• Otitis Media (OM): Middle ear infection, often following a cold. The Eustachian tube, connecting the middle ear to the throat, facilitates spread during colds. Fluid buildup puts pressure on eardrum, causing ear pain and sometimes reduced hearing. More common in children due to smaller Eustachian tubes and reduced immunity. Typically viral, but sometimes bacterial. Often self-limiting.
• Common Cold (Viral Rhinitis): Caused by rhinoviruses, coronaviruses, or adenoviruses. Mild symptoms include nasal congestion, runny nose, sore throat, cough, and sneezing.
• Influenza (Flu): Caused by influenza viruses (types A, B, and rarely C). Shows sudden onset of high fever, chills, headache, muscle aches, fatigue, dry cough, and sore throat. Can lead to severe complications (pneumonia) in high risk individuals.
• Sinusitis (Sinus Infection): Often follows a viral URTI or allergies. Symptoms include facial pain or pressure, nasal congestion, headache, and post-nasal drip. Can be bacterial.
• Strep Throat (Streptococcal Pharyngitis): Caused by Group A Streptococcus (Streptococcus pyogenes). Symptoms include severe sore throat, difficulty swallowing, fever, and swollen tonsils with white patches. Left untreated, can lead to complications like rheumatic fever or post-streptococcal glomerulonephritis.
• Bronchitis: Typically a lower RTI, also affects trachea (part upper RTI). Inflammation of bronchial tubes, frequently viral. Symptoms include persistent cough, sometimes with sputum production, chest discomfort, and low-grade fever. Treatment with antibiotics may be necessary for bacterial bronchitis.

Pathogenesis

• Most URTIs are caused by viruses
• Microbes spread to cause localized infection or spread throughout the body
• The immune response (adaptive) may be needed to resolve an infection

Virulence Factors

• Crucial for bacteria to cause infection - bacteria must colonize, multiply, and evade the immune system.
• Examples include pili (adhesins), capsules, M proteins, and toxin production.

Influenza (detailed)

• Influenza viruses (types A, B, and C)
• Transmission by droplet inhalation and contact
• Antigenic variation causes changes in the virus's form over time (antigenic drift or shift)
• Major historical influenza outbreaks include Spanish Flu, Asian Flu, Hong Kong Flu, Russian Flu, H5N1, and 2008 flu or swine flu.

Treatment & Prevention (Influenza)

• Vaccination is the foremost preventive measure
• Treatment should begin within 48 hours of symptom onset.
• Neuraminidase inhibitors (oseltamivir, zanamivir) limit infection severity.
• Amantadine blocks virus uncoating in the host cell.

URTI Bacterial Causes & Treatment

• Streptococcus pyogenes: Most common cause of pharyngitis; treat with penicillin.
• Streptococcus pneumoniae: Causes sinusitis, pneumonia, otitis media; treat with penicillin (check resistance guidelines).
• Haemophilus influenzae: Common in children, causing sinusitis and otitis media; Hib vaccine significantly reduced severe infections.
• Staphylococcus aureus: Often associated with skin infections but can cause sinusitis/otitis media in susceptible individuals; treat with flucloxacillin
• Moraxella catarrhalis: May cause sinusitis and otitis (in adults/children with underlying respiratory conditions, like cystic fibrosis).
• Bordetella pertussis: Causes whooping cough—severe coughing fits; vaccination highly effective in reducing this disease.

Complications of Streptococcus pyogenes

• Otitis media, sinusitis, mastoiditis
• Scarlet fever
• Rheumatic fever (myocarditis/pericarditis)
• Rheumatic heart disease
• Acute glomerulonephritis

Additional Information

• Mumps is a viral infection causing swelling in the parotid salivary glands. It can cause complications in males, and is generally self-limiting.
• Investigations for URTIs are usually not necessary except for suspected strep throat (throat swab).

Treatment Options (Bacterial URTI)

• For bacterial infections like tonsillitis, sinusitis, and otitis media, phenoxymethylpenicillin is a common treatment. Alternatives include clarithromycin or doxycycline (caution with children). Amoxicillin is an often used alternative.