Pulmonary Infectious Diseases Overview

Pulmonary Infectious Diseases

• Pulmonary infections are a broad category of diseases affecting the lungs, encompassing various types of pneumonia and other conditions.
• The presentation covers community-acquired bacterial pneumonia, community-acquired interstitial pneumonia, nosocomial pneumonia, and aspiration pneumonia.
• Chronic pneumonia, caused by Mycobacterium tuberculosis, Histoplasma capsulatum, Blastomyces dermatitides, and Coccidioides immitis, is also discussed.
• Opportunistic infections in HIV patients are highlighted.
• Pneumonia is an infection of the lung parenchyma.
  • Decreased systemic resistance of the host is a factor in pneumonia, contributing factors include chronic diseases, immunologic deficiencies, leukopenia, and treatment with immunosuppressive agents.
  • Impaired local defense mechanisms contribute to pneumonia. Examples include loss of cough reflex, problems with the mucociliary apparatus (e.g., immotile cilia syndrome), accumulation of secretions, and interference with alveolar macrophage activities (e.g., by alcohol or tobacco smoke).

Session Objectives

• Students will become familiar with mechanisms leading to bacterial and interstitial pneumonia, and their morphology.
• Define healthcare-associated pneumonia (nosocomial), aspiration pneumonia, and lung abscess.
• Explain the morphology of chronic pneumonia caused by various pathogens (Mycobacterium tuberculosis, Histoplasma capsulatum, Blastomyces dermatitides, Coccidioides immitis).
• Describe morphology of pneumonia caused by opportunistic agents in HIV patients.

Pneumonia Classification

• The presentation describes various categories of pneumonia, including community-acquired, healthcare-associated (nosocomial), and aspiration pneumonia.
• A detailed breakdown of bacterial, viral (influenza type A), fungal (histoplasmosis, blastomycosis, coccidioidomycosis) types are categorized.

Bacterial Pneumonia

• Alveoli (air sacs in the lungs) show inflammatory exudate, leading to consolidation ("solidification") of pulmonary tissue.
• Predisposing conditions include extremes of age, chronic diseases (congestive heart failure, COPD, diabetes), congenital/acquired immune deficiencies, and decreased/absent splenic function, which increase the risk of infection with encapsulated bacteria like pneumococcus.
• Clinical features include abrupt onset of high fever, shaking chills, mucopurulent cough with sputum or sometimes hemoptysis, and pleuritic pain (if pleuritis is present).
• The clinical picture is significantly changed (altered and improved) with antibiotics. Clinically improving patients may become afebrile within 48-72 hours of antibiotic therapy.

Bacterial Pneumonia Morphology

• Bronchopneumonia: patchy consolidation, common in infancy and old age, spreading to involve large areas of a lobe or the entire lung from previous bronchitis or bronchiolitis.
• Lobar pneumonia: involves a large portion or the whole lung resulting in consolidation.
• The same organisms (e.g., S. pneumoniae, Legionella, Klebsiella) may cause either pattern, depending on patient susceptibility.

Natural History of Lobar Pneumonia

• Progressive stages of lobar pneumonia are detailed, with phases of congestion, red hepatization, gray hepatization, resolution.

Chronic Pneumonia

• Often involves a localized lesion in immunocompetent patients, possibly with lymph node involvement.
• Caused by bacteria (Mycobacterium tuberculosis) or fungi (histoplasmosis, blastomycosis and coccidioidomycosis).
• Mycobacterium tuberculosis causes granulomatous inflammation, histoplasmosis is a fungal infection, and blastomycosis is another fungal infection, while coccidioidomycosis is caused by two species of fungi.

Primary and Secondary Tuberculosis

• This describes the characteristics of primary tuberculosis:
  • Early stage, localized granuloma/inflammation, with a possibility of draining to lymph nodes causing caseation.
  • Commonly found in the apex of the lungs (upper lobes) of the lung with central necrosis.
• Secondary tuberculosis/Reactivation Tuberculosis is typically found in immunocompetent individuals.
• The pneumonia lesion grows initially and then develops fibrosis, a scar, granuloma and central caseation.

Histoplasmosis

• Acquired by inhaling spores from contaminated soil, typically from bird or bat droppings.
• Affects immune-compromised severely.
• Macrophages ingest, but don't kill, the organism without assistance from T-cells, with help, the macrophages kill the fungus.
• Histological characteristics are detailed, including granulomas and yeast forms.

Blastomycosis

• Pneumonia resolved spontaneously in most cases, however, can progress to a chronic form.
• In normal hosts, lung lesions are often characterized by, suppurative granulomas.
• Lesions can be disseminated to other systems.
• Macrophages have limited ability to kill the fungus.

Coccidioidomycosis

• Involves a delayed-type hypersensitivity reaction.
• In most cases, the lung infection is resolved spontaneously.
• Involves the skin and meninges in disseminated infections.
• Organisms can be ingested by macrophages but resist intracellular killing, preventing phagosome-lysosome fusion (meaning the fungus can't be destroyed).

Pneumonia in Immunocompromised Hosts

• Presentation of a pulmonary infiltrate may occur without infection.
• Includes a wide range of opportunistic pathogens, such as bacteria, fungi, and viruses.

Pulmonary Infections in HIV Patients

• "Typical" bacterial pneumonias are common in HIV patients.
• S. pneumoniae, S. aureus, H. influenzae, and gram-negative rods are frequently implicated.
• Bacterial infections tend to become severe if bacteremia occurs.
• Opportunistic infections are also important considerations in this patient population (Pneumocystis, CMV).

Pneumonia in HIV Infection/Immunocompromised Host

• Several opportunistic infections (e.g., Pneumocystis carinii, CMV, Cryptococcus) are notable.
• Specific features and characteristics of each opportunistic infection are addressed in these sections.