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.