Pneumonia

Pneumonia is an acute infection of the lungs. In order to classify as pneumonia, the pathogen must reach the alveoli of the lungs.

The respiratory tract has a number of defense systems that need to be overwhelmed in order for pneumonia to occur. Respiratory secretions contain antimicrobial compounds including alpha-1-antitrypsin, lysozyme, and lactoferrin. The alveoli contain macrophages and dense vasculature with the capability of delivering lymphocytes, granulocytes and lymphatic drainage directly to the area in a short period of time. The upper respiratory tract includes a lot of IgA, and the lower respiratory tract contains IgG to neutralize viral and bacterial infections.

If any of these systems is overwhelmed, bacterial or viral infection can reach the alveoli of the lungs. Common causes include deficient neutrophil quality or quantity, deficient immunoglobulins, or deficient respiratory tract secretions.

Typical symptoms include a productive cough, fever and chills, shortness of breath, and chest pain that is often worse on breathing in. Fatigue, sweating, and a rapid heart rate are common, and older or frail patients may instead present with confusion or general decline.

Diagnosis is based on the combination of clinical features and examination findings such as crackles, bronchial breathing, and dullness to percussion over the affected area. A chest X-ray typically confirms areas of consolidation, while blood tests and sputum culture help assess severity and identify the causative organism.

Pneumonia is more frequent and more severe in people with chronic lung disease, heart failure, diabetes, or a weakened immune system. Complications can include pleural effusion, lung abscess, and spread of infection to the bloodstream (sepsis).