Pneumonitis, Lobar Pneumonia, Bronchopneumonia, Viral Pneumonia, Bacterial Pneumonia
What is Pneumonia?
Pneumonia is a general term used to describe inflammation of the lungs due to infection. Most cases of pneumonia are caused by viruses or bacteria, but it can also be caused by mycoplasma (an organism intermediate between a bacterium and a virus), fungus, yeast, protozoa, or C. psittaci (a bacteria-like organism caught from birds). Whatever the cause, the organism multiplies, resulting in an inflammatory reaction within the small air spaces of the lung (alveoli). The alveoli fill up with fluid and white blood cells, interfering with the lung's ability to receive oxygen. This process can occur gradually or quickly, depending on the potency of the infecting organism and the ability of the body's immune system to fight off the infection. Pneumonia can be mild enough to be cured with oral antibiotics and a few days rest, or it can be severe enough to require hospitalization in an intensive care unit. Death may occur as a result of respiratory failure.
What is Pneumonitis?
Pneumonitis is a term that also refers to inflammation of the lungs. It may be due to infection, an allergic reaction (caused by inhalation of dust containing animal or plant material), exposure to radiation, accidental inhalation of vomit or other liquid (aspiration pneumonia), or as a rare side effect of certain drugs (acebutolol, azathioprine).
Types of Pneumonia
Several classification systems are used to define the types of pneumonias.
- One system classifies pneumonia by its anatomic location within the lungs. If the pneumonia involves all or most of the alveoli in just one lobe of the lung, it may be called "lobar pneumonia."
- If the pneumonia starts in the bronchi and bronchioles (airways) and then spreads to patches of tissue in one or both lungs, it may be called "bronchopneumonia."
- Another classification system is based on whether the symptoms are "typical pneumonia" or "atypical pneumonia."
- Pneumonia may also be classified by its place of origin. Pneumonia acquired in a hospital setting is referred to as "nosocomial" pneumonia, while pneumonia acquired in the community is referred to as "community acquired" pneumonia.
Although each of these classifications supply some helpful information about the characteristics of an individual's pneumonia, the most important classification is the one that is based on the organisms causing the infection.
For example, pneumonia can be referred to as viral, pneumococcal, staphylococcal, or Klebsiella pneumonia according to the infecting agent.
Viral infections make up about one-half of all cases of pneumonia. Most often caused by influenza viruses, viral pneumonia can also be caused by the chickenpox virus or by adenovirus (a group of related viruses that cause respiratory tract infections). Because it is caused by a virus rather than a bacterium, viral pneumonia does not generally respond well to antibiotics.
What is Bacterial pneumonia?
Pneumonia is the sixth leading cause of death in the US and the fourth leading cause of death among the elderly.
Bacterial pneumonia is more common in the adult population. Bacteria may enter the alveoli of the lungs by four routes: inhalation from the surrounding air, spread via the bloodstream from an infection elsewhere within the body, contact with nearby infected sites, or by inhaling organisms growing in the individual's mouth or throat. Because pneumonia tends to occur when the defenses that normally protect the lower respiratory tract are overwhelmed by pathogenic agents, a recent illness such as influenza can lead to pneumonia.
Other risk factors include adults over the age of 60, malnutrition, smoking, alcoholism, and drug addiction. Pneumonia can also occur if the body's overall immune system has been compromised by chronic medical conditions, such as cystic fibrosis, congestive heart failure, chronic obstructive pulmonary (lung) disease, cancer, diabetes, cirrhosis of the liver, or kidney failure.
AIDS, chemotherapy against cancer, and corticosteroid therapy can also result in a depressed immune system. It is estimated that each year over one million cases of community acquired pneumonia are severe enough to require hospitalization. These infections are usually viral or bacterial in origin, with rare instances of fungal or parasitic infection. Hospital acquired (nosocomial) pneumonia is diagnosed in over 275,000 individuals per year, and has a very high mortality rate.
How is it diagnosed?
History: Typical symptoms of pneumonia include sudden onset, shortness of breath, fever, chills, headache, and muscle pain (myalgia). A cough may produce yellow-green sputum and occasionally blood. Chest pain is worse on inspiration (breathing in) because of inflammation in the membranes that line the lungs and chest cavity (pleurisy).
Symptoms of viral and atypical pneumonia differ in that the fever is not accompanied by chills, and the cough is dry and non-productive (no mucus is coughed up). Flu-like symptoms include headache, muscle pain, and weakness may be present. Within 12 to 36 hours, breathlessness may increase accompanied by a worsening cough that now produces a small amount of mucus. Typical respiratory symptoms may be masked in the elderly and in individuals taking corticosteroids or aspirin. These individuals may instead present with confusion, lethargy, and an elevated respiratory rate.
To assist in identifying exposure to less common infectious organisms, the medical history should include a complete history of the illness (including non-respiratory symptoms such as rash, diarrhea, nausea, and mental status), and a history of the individual's occupation, hobbies, pets, and recent travel. Also helpful to know is if there is a history of alcoholism, swallowing difficulties, or decreased mental alertness, all of which can cause inhalation of food or liquid into the lungs (aspiration pneumonia).
Physical exam: On physical exam, breathing may be labored, using accessory muscles in the neck, chest and abdomen. In severe pneumonia, the individual may exhibit a respiratory rate above 30 breaths per minute. Listening through a stethoscope (auscultation) may reveal abnormal breath sounds indicating fluid in the lungs (rales), or areas lacking air exchange (consolidative breath sounds).
Tests: A chest x-ray can establish the diagnosis of pneumonia, determine the extent of lung infection, and track the progression of the disease. A complete blood count (CBC) is routinely obtained, but viral pneumonias do not produce the high white cell count generally associated with bacterial pneumonia. Blood oxygen level is often low. Culture of a sputum sample may be done to identify the infecting organism. Rarely, a bronchoscopy or an open lung biopsy (surgical removal of tissue for microscopic examination) may be required in analyzing very difficult cases, or pneumonia that occurs in immunocompromised individuals.
How is Pneumonia treated?
Antibiotics are the mainstay of treatment for most pneumonias. In mild to moderate cases, oral antibiotics are given for the most likely causative organisms. If an individual does not begin to respond to the selected antibiotic therapy in two to three days, additional diagnostic tests may be performed to pinpoint the causative agent, and the medication changed accordingly.
Supportive therapy includes increased fluid intake (hydration) and agents to thin and mobilize secretions (mucolytic and mucokinetic agents), medication to widen the airways in the lungs (bronchodilators), cough suppressants, and medication to reduce fever (antipyretics) and reduce pain (analgesics).
Viral pneumonia, most often caused by influenza viruses, does not respond effectively to antibiotic therapy unless a secondary bacterial infection develops in the lungs. Although various anti-viral agents can be used, depending on the specific vial pathogen, there is no effective drug treatment for most viral pneumonias. General treatment measures include adequate fluid intake and analgesics for chest pain. Oxygen is administered only if the individual becomes hypoxic (oxygen deprived).
Individuals with severe pneumonia often require hospitalization to provide supplemental oxygen, respiratory therapy, intravenous antibiotics, and intravenous fluids. Individuals with multiple risk factors indicating poor outcome from pneumonia (such as those with chronic underlying medical conditions) may also be treated in the hospital setting for closer observation. Preventive treatment with vaccines is possible for influenza, viral, and pneumococcal pneumonias.
What might complicate it?
Viral infection can progress into a bacterial infection. Pneumonia can cause fluid to accumulate in the space between the lung and the chest wall (pleural effusion). This fluid can then become infected (empyema), spreading the infection to the blood stream (sepsis). As a result, other tissues may become infected, including joints (arthritis), membranes lining the brain and spinal cord (meningitis), the brain itself (encephalitis), or kidneys (nephritis). Septic shock, a severe complication, results when multiplying bacteria release toxins into the bloodstream.
Other serious complications include respiratory failure or the development of an abscess in the lung. Individuals with chronic medical conditions such as diabetes, heart disease, kidney disease, or lung disease often experience a worsening of their medical condition during pneumonia.
The outcome for any individual diagnosed with pneumonia is quite variable. It will depend on the overall health and immune competence of the individual, the virulence of the organism causing the pneumonia, and the effectiveness of the prescribed treatment. Most cases of mild to moderate pneumonia respond well to oral antibiotic therapy. However, elderly or debilitated individuals may fail to respond to treatment. As a result, more and more of their lung tissue becomes affected. Death may occur as a result of respiratory failure.
In general, pneumonia that requires hospitalization and intensive care has a mortality rate of 25% to 50%. Pneumonia acquired in the hospital setting (nosocomial pneumonia) has an even higher mortality rate.
Conditions with similar symptoms include bronchitis, chronic obstructive pulmonary disease (COPD), pulmonary embolism, asthma, bronchiectasis, tuberculosis, cancer, congestive heart failure, and AIDS. The adult respiratory distress syndrome (ARDS) is a non-infectious, serious lung disease with some similarities to pneumonia.
Internist, pulmonologist and infectious disease specialist.
Last updated 28 May 2021