Bacterial Diseases of the Respiratory System

Diseases of the Upper Respiratory System

Laryngitis & Tonsillitis

• Caused by:

  • Streptococcus pneumoniae, Streptococcus pyogenes, and viruses.

• Symptoms: Inflammation of the larynx (voice box) or tonsils, causing sore throat and difficulty speaking/swallowing.

Sinusitis

• Cause: Generally bacterial infection of the sinuses.

• Symptoms: Nasal congestion, pressure, facial pain.

Epiglottitis

• Causative agent: Haemophilus influenzae.

• Symptoms: Swelling of the epiglottis, which can obstruct the airway—medical emergency.

Scarlet Fever (Scarlatina)

Cause

• Group A Streptococcus (Streptococcus pyogenes).

• Produces erythrogenic toxin → responsible for red rash.

Epidemiology

• Common in children aged 2–8.

• Highly contagious, spreads via close contact (e.g., nurseries, schools).

Symptoms

• Fever, sore throat, red rash, strawberry tongue, flushed cheeks.

• Skin may peel as the rash fades.

Treatment

• Easily treated with antibiotics.

Complications

• If untreated:

  • Local: Ear infections, sinusitis, abscesses.

  • Systemic: Septicaemia, meningitis, arthritis, cellulitis.

  • Delayed: Heart, kidney, or joint problems.

New Strain

• emm1 (M1UK) strain with increased SpeA toxin production.

• Greater invasive potential, explaining increased recent incidence.

Diphtheria

Cause

• Corynebacterium diphtheriae (Gram-positive rod).

• Toxin produced only if bacterium is lysogenised (infected by a phage).

Pathology

• Thick grey membrane in throat: composed of fibrin, dead cells, and bacteria.

• Cutaneous diphtheria: Chronic skin ulcers.

Prevention

• Diphtheria toxoid vaccine (part of DTaP).

Diseases of the Lower Respiratory System

Pertussis (Whooping Cough)

Cause

• Bordetella pertussis (Gram-negative coccobacillus).

Virulence factors

• Tracheal cytotoxin damages ciliated cells.

• Pertussis toxin disrupts immune responses.

Stages

1. Catarrhal stage – mild, cold-like.

2. Paroxysmal stage – severe coughing fits.

3. Convalescent stage – slow recovery.

At-Risk Groups

• Infants: high risk for complications—seizures, brain damage, fatalities.

• Pregnancy: Vaccine recommended to pass antibodies to newborn.

Immunity

• Vaccine immunity wanes over time.

• Re-infections can occur, spreading the disease to vulnerable individuals.

Tuberculosis (TB)

Cause

• Mycobacterium tuberculosis (MTB):

  • Obligate human pathogen.

• Other species:

  • M. bovis (from cattle).

  • M. avium-intracellulare (opportunistic in late-stage HIV).

Transmission

• Airborne droplets (human to human).

• Infects lungs → can disseminate (miliary TB).

Types of TB

• Pulmonary TB: Chronic cough, blood-stained sputum (haemoptysis).

• Miliary TB: Disseminated lesions across body via blood.

Treatment

• First-line drugs:

  • Isoniazid (INH), Rifampicin, Pyrazinamide (PZA), Ethambutol (EMB).

Drug Resistance

• MDR: Multi-drug resistant.

• XDR: Extensively drug resistant.

• TDR: Totally drug resistant.

• TB drug resistance is a global concern.

Decline & Resurgence

• Previously declined due to housing, nutrition, and screening.

• London once had 50% of UK cases.

• Now rising due to:

  • Immigration from high-incidence countries.

  • Social and global changes.

  • HIV co-infection (accelerates progression from infection to disease).

Vaccination

• BCG vaccine: Not part of routine UK schedule since 2005.

• Offered to:

  • Babies at risk (e.g., family from high TB regions).

  • Healthcare workers or those exposed to animals.

Pneumonia

Definition

• Inflammation of lung tissues.

• Alveoli fill with fluid → affects gas exchange.

At-Risk Groups

• Infants, elderly, smokers, or immunocompromised individuals.

Types of Pneumonia

Pneumococcal Pneumonia

• Streptococcus pneumoniae (Gram-positive diplococci).

• Penicillin is effective.

Haemophilus Influenzae Pneumonia

• H. influenzae (Gram-negative coccobacillus).

• Risk factors: Alcoholism, diabetes, cancer.

• Treated with second-gen cephalosporins.

Mycoplasmal Pneumonia

• Mycoplasma pneumoniae (pleomorphic, no cell wall).

• Walking pneumonia – mild, common in young people.

• Diagnosed via PCR or IgM antibody tests.

Legionellosis

• Legionella pneumophila (Gram-negative, intracellular).

• Source: Water (e.g., air conditioning).

• Not spread person-to-person.

• Pathogenesis:

  • Inhaled → alveoli → engulfed by macrophages.

  • Replicates in vacuoles → kills macrophages.

  • Tissue damage from both host immune response and bacterial proteases.

• Treated with erythromycin.

Psittacosis (Ornithosis)

Cause

• Chlamydophila psittaci (Gram-negative, intracellular).

• Spread by bird droppings (inhaled).

• Inside body: transforms into reticulate body to replicate.

• Treated with tetracycline.

Fungal Pneumonias

General

• Rare in healthy UK individuals.

• More common in immunocompromised.

• Often associated with travel to endemic regions.

Examples

• Histoplasmosis

• Pneumocystis

• Coccidioidomycosis

• Blastomycosis

Opportunistic Fungi

• Aspergillus

• Rhizopus

• Mucor

✅ Key Takeaways

• Upper respiratory infections are mostly caused by Streptococcus spp. or viruses.

• Scarlet Fever is a childhood illness caused by S. pyogenes with increased cases linked to a new, more virulent strain.

• Diphtheria is rare due to vaccination but potentially fatal.

• Pertussis (Whooping cough) is dangerous in infants—waning immunity means booster shots (e.g. during pregnancy) are crucial.

• Tuberculosis remains a global health issue with emerging drug resistance and close links to HIV.

• Pneumonia can be caused by several bacteria; treatment varies depending on the organism.

• Legionella infection is linked to water systems and causes lung damage through immune overreaction.

• Psittacosis is a zoonotic infection linked to birds.

• Fungal pneumonias mainly affect immunocompromised individuals and travellers.