Riassunto esame Pneumologia, prof. Centanni, libro consigliato Pulmonary Infections and Pneumonia, Robbins

Pulmonary infections and pneumonia

Respiratory tract infections are more frequent than infections to other organs. The vast majority are viral infections of the upper respiratory tract, but bacterial, viral, mycoplasmal, and fungal infections of the lung account for a significant amount of morbidity, leading to 1/6 deaths in the US.

Pneumonia

Pneumonia is broadly defined as an infection of the lung parenchyma. It may occur when local pulmonary defenses are impaired or when systemic resistance to hosts is lowered, for example, in chronic diseases, immunological deficiency, or treatment with immunosuppressive agents.

Local defense mechanisms of the lung can be lowered by many factors:

• Loss or suppression of cough reflex (coma, anesthesia, neuromuscular disorders, drugs, or chest pain) may lead to aspiration of gastric contents.
• Injury of mucociliary apparatus (cigarette smoke, corrosive gas inhalation, viral diseases, genetic defects).
• Accumulation of secretions (cystic fibrosis or bronchial obstruction).
• Interference with bactericidal and phagocytic function of alveolar macrophages (smoke, alcohol, anoxia, O₂ intoxication). Anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen".
• Pulmonary congestion or edema.

Defects in innate immunity and humoral immunodeficiency lead to an increased incidence of pyogenic bacteria. Cell-mediated immune defects increase the incidence of intracellular pathogens, such as mycobacteria and herpes virus. One type of pneumonia can predispose to the development of another type, for example, the development of bacterial pneumonia on the basis of viral influenza. The major portal of entry is the respiratory tract, but hematogenous spread can occur. Many patients acquire terminal pneumonia while hospitalized (nosocomial), where bacteria may have acquired resistance to antibiotics, facilitated spread, and equipment contamination.

Community acquired pneumonias

Community-acquired pneumonia (CAP) is one of several diseases in which individuals who have not recently been hospitalized develop an infection of the lungs (pneumonia). It may be bacterial or viral; bacterial infection often follows viral infection. Bacterial invasion of the lung causes alveoli to be filled with inflammatory exudate, leading to consolidation of parenchyma.

Predisposing conditions include:

• Extremes of age;
• Chronic diseases (COPD, heart failure, diabetes);
• Congenital or acquired immune deficiencies;
• Decreased or absent splenic functions (sickle cell disease, post-splenectomy) which increase the risk of infection with encapsulated bacteria.

S. pneumoniae

The most common cause of community-acquired pneumonia. Gram-stained sputum is important for diagnosis, showing numerous neutrophils and Gram-positive lancet-shaped diplococci. It's part of the endogenous flora, leading to possible false positives. Blood cultures may be performed but are less sensitive, with only 20-30% of patients positive in the first phases of the disease. Pneumococcal vaccines are recommended in high-risk patients.

H. influenzae

Pleomorphic Gram-negative organism. Pleomorphism, in microbiology, is the ability of some bacteria to alter their shape or size in response to environmental conditions. A major cause of life-threatening lower respiratory tract infections and meningitis in children, H. influenzae is a common cause of community-acquired acute pneumonia and is an ubiquitous colonizer of the upper respiratory tract. It exists in two forms: encapsulated (5%) and unencapsulated (95%). Vaccines are available. Pili aid adherence to the mucosa and secretion of factors inhibit mucociliary function. Protease degrades...