Community-acquired pneumonia (CAP) refers to pneumonia (any of several lung diseases) contracted by a person outside of the healthcare system. In contrast, hospital-acquired pneumonia (HAP) is seen in patients who have recently visited a hospital or who live in long-term care facilities. CAP is common, affecting people of all ages, and its symptoms occur as a result of oxygen-absorbing areas of the lung (alveoli) filling with fluid. This inhibits lung function, causing dyspnea, fever, chest pains and cough. CAP, the most common type of pneumonia, is a leading cause of illness and death worldwide. Its causes include bacteria, viruses, fungi and parasites. CAP is diagnosed by assessing symptoms, performing a physical examination, by x-ray or by sputum examination. Patients with CAP sometimes require hospitalization, and it is treated primarily with antibiotics, antipyretics and cough medicine. Some forms of CAP can be prevented by vaccination and by abstaining from tobacco products. Signs and symptoms
Common symptoms
Coughing which produces greenish or yellow sputum
A high fever, accompanied by sweating, chills and shivering
Sharp, stabbing chest pains
Rapid, shallow, often painful breathing

Less-common symptoms
Coughing up blood (hemoptysis)
Headaches, including migraines
Loss of appetite
Excessive fatigue
Bluish skin (cyanosis)
Nausea
Vomiting
Diarrhea
Joint pain (arthralgia)
Muscle aches (myalgia)
Rapid heartbeat
Dizziness or lightheadedness

In the elderly
New or worsening confusion
Hypothermia
Poor coordination, which may lead to falls

In infants
Unusual sleepiness
Yellowing of the skin (jaundice)
Difficulty feeding

Complications
Major complications of CAP include:

Sepsis - A life-threatening reaction to infection. A common cause of sepsis is bacterial pneumonia, frequently the result of infection with streptococcus pneumoniae. Patients with sepsis require intensive care with blood pressure monitoring and support against hypotension.
Pseudomonas aeruginosa, an uncommon cause of CAP, is a difficult bacteria to treat. Bacteria and fungi typically enter the lungs by inhalation of water droplets, although they can reach the lung through the bloodstream if an infection is present. In the alveoli, bacteria and fungi travel into the spaces between cells and adjacent alveoli through connecting pores. The immune system responds by releasing neutrophil granulocytes, white blood cells responsible for attacking microorganisms, into the lungs. The neutrophils engulf and kill the microorganisms, releasing cytokines which activate the entire immune system. This response causes fever, chills and fatigue, common symptoms of CAP. The neutrophils, bacteria and fluids leaked from surrounding blood vessels fill the alveoli, impairing oxygen transport. Bacteria may travel from the lung to the bloodstream, causing septic shock (very low blood pressure which damages the brain, kidney, and heart). Parasites
A variety of parasites can affect the lungs, generally entering the body through the skin or by being swallowed. They then travel to the lungs through the blood, where the combination of cell destruction and immune response disrupts oxygen transport. Diagnosis
Patients with symptoms of CAP require evaluation. Diagnosis of pneumonia is made clinically, rather than on the basis of a particular test. Evaluation begins with a physical examination by a health provider, which may reveal fever, an increased respiratory rate (tachypnea), low blood pressure (hypotension), a fast heart rate (tachycardia) and changes in the amount of oxygen in the blood.