Understanding Pneumonia: Types, Causes, Treatments and Preventions

Pneumonia is a form of acute respiratory infection that affects the lungs. It is characterised by inflammation of the alveoli, the air sacs of the lungs where the gas exchange of oxygen and carbon dioxide occurs. When an individual has pneumonia, the alveoli fill with pus and fluid, limiting oxygen intake and making it hard to breathe. In vulnerable populations, it is a disease of poverty and occurs most commonly when a child’s developing immune system is weakened by malnutrition, air pollution, co-infections with HIV/AIDS or  measles, and low birthweight.

Not only is it the largest single cause of death in young children, but in those that do survive, pneumonia increases their risk of developing chronic pulmonary disorders later in adult life. In wealthier nations, adults over 65 years of age and people with chronic health problems bear the greater burden of pneumonia. The combined death rate for pneumonia and influenza positions these respiratory infections as the sixth leading cause of death in Australia. Indigenous Australians are disproportionately affected. Compared to the non-indigenous population. Indigenous Australians have a 4-fold greater hospitalisation rate from pneumonia and a 9 to 11-fold greater mortality rate from respiratory infections.

Causes of Pneumonia

There are five main causes of pneumonia of which bacteria and viruses are the most common.

• Bacteria
• Viruses
• Mycoplasmas
• Other infectious agents, such as fungi
• Various chemicals

Bacterial Pneumonia

Bacterial pneumonia can occur on its own or it can develop after a cold or the flu. People at greatest risk for bacterial pneumonia include people recovering from surgery, people with respiratory diseases or viral infections and people who have weakened immune systems.

If the body’s defences are weakened—by illness, old age, malnutrition, or impaired immunity—the pneumonia bacteria, which can live in healthy throats, can multiply and work their way into the lungs.

The infection can quickly spread through the bloodstream and invade the entire body.  

Many different types of bacteria can cause pneumonia

• The most common cause of bacterial pneumonia in adults is Streptococcus pneumoniae (pneumococcus), but there is a  vaccine available for this form of pneumonia.
• Atypical or "walking" pneumonia is a form of pneumonia that is characterised by symptoms similar to those of the flu and is generally less serious than other types of pneumonia. Causes of atypical pneumonia include: Legionella pneumophila, Mycoplasma pneumoniae, and Chlamydophila pneumoniae. Widespread outbreaks of mycoplasma pneumonia occur every 4 to 8 years.
   
• Other bacteria that can cause pneumonia include Staphylococcus aureus, Moraxella catarrhalis, Streptococcus pyogenes, Neisseria meningitidis, Klebsiella pneumoniae, and Haemophilus influenzae.

Viral pneumonia

Viruses are the most common cause of pneumonia in children and young adults. Most of these pneumonias are not serious and last a short time but others can be severe. Viral pneumonia is most often caused by one of several viruses:

• Adenovirus
• Influenza
• Parainfluenza
• Respiratory syncytial virus
• Rhinovirus
• Herpes simplex virus
• Severe acute respiratory syndrome (SARS) virus

Viral pneumonia caused by the influenza virus may be severe and sometimes fatal. The virus invades the lungs and multiplies; however, there are almost no physical signs of lung tissue becoming filled with fluid. This pneumonia is most serious in people who have pre-existing heart or lung disease and pregnant women. In extreme cases, the patient has a desperate need for air and extreme breathlessness. Viral pneumonias may be complicated by an invasion of bacteria, with all the typical symptoms of bacterial pneumonia.

The SARS virus is caused by a member of the coronavirus family. When someone with SARS coughs or sneezes, infected droplets spray into the air. You can catch the SARS virus if you breathe in or touch these particles. The SARS virus may live on hands, tissues, and other surfaces for up to 6 hours in these droplets and up to 3 hours after the droplets have dried. The death rate from SARS is 9 to 12% of those diagnosed. In people over age 65, the death rate is higher than 50%. The illness is milder in younger patients. Public health policies have been effective at controlling outbreaks. Many nations have stopped the epidemic in their own countries. All countries must continue to be careful to keep this disease under control.

Other Types of Pneumonia

Mycobacterium tuberculosis can cause pneumonia (tuberculosis pneumonia). This bacterium usually attacks the lungs, but can also attack other parts of the body such as the kidney, spine, and brain. If not treated properly, tuberculosis can be fatal. Tuberculosis was once the leading cause of death in the United States.

Pneumocystis jiroveci pneumonia is caused by an organism believed to be a fungus. At first, the name Pneumocystis carinii was applied to the organism found in both rats and humans, as it was not yet known that the parasite was host-specific. In 1976, the name "Pneumocystis jiroveci" was proposed for the first time, to distinguish the organism found in humans from variants of Pneumocystis in other animals. Pneumocystis jiroveci may be the first sign of illness in many persons with AIDS. Pneumocystis jiroveci can be successfully treated in many cases. It may recur a few months later, but treatment can help to prevent or delay recurrence. Various less common pneumonias are caused by the inhalation of food, liquid, gases or dust, and by fungi. Rickettsiae are bacteria found in ticks, lice, fleas, mites, chiggers, and mammals. Q fever, also called rickettsial pneumonia, is caused by the rickettsia, Coxiella burnetii.

Transmission of  Rickettsiae by the bite of infected ticks or mites is deemed to be rare in humans. The common mode of infection appears to be by inhalation of contaminated material shed into the environment by infected livestock. Measles, caused by the rubeola virus, infects the respiratory tracts of nearly all affected persons. Pneumonia is the most common severe complication of measles and accounts for most measles-associated deaths.

Symptoms of Pneumonia

The most common symptoms  of pneumonia include:

• Cough (some pneumonias cause greenish or yellow mucus, or even bloody mucus)
• Fever, which may be mild or high
• Shaking chills
• Shortness of breath

Symptoms also can vary, depending on whether the pneumonia is bacterial or viral:

• In bacterial pneumonia, your temperature may rise as high as 40.5 degrees Celsius. This pneumonia causes profuse sweating, and rapidly increased breathing and pulse rate. Lips and nailbeds may have a bluish color due to lack of oxygen in the blood. A patient's mental state may be confused or delirious.
• The initial symptoms of viral pneumonia are the same as influenza symptoms: fever, a dry cough, headache, muscle pain, and weakness. Within 12 to 36 hours, there is increasing breathlessness; the cough becomes worse and produces a small amount of mucus. There is a high fever and there may be blueness of the lips.

Differentiating Pneumonia from other Respiratory Illnesses

Distinguishing pneumonia from other pulmonary pathologies, such as acute chronic obstructive pulmonary disease (COPD) or asthma exacerbation, can often present a significant challenge, particularly in patients with these underlying lung diseases.

Patients with pneumonia had increased procalcitonin and C-reactive protein levels compared with those patients with asthma. In most circumstances, virologic tests are the mainstay of precise etiologic diagnosis. Rapid antigen detection kits can provide results within hours, making them useful in the emergency department. The sensitivity and specificity of these kits varies between 80% and 95%. High-resolution computerised tomography (CT) scan can be useful in patients who have respiratory symptoms but normal results on chest films; additional information is needed on chest radiographic findings, or to look for concurrent parenchymal or pleural disease. CT scanning can also be quite beneficial in guiding diagnostic maneuvers such as bronchoscopy, bronchoalveolar lavage, or lung biopsy. Despite the inability to make a specific diagnosis from a CT scan, it may be helpful in differentiating infectious from noninfectious acute parenchymal lung diseases.

Classifying Pneumonias 

Pneumonias can be classified in several ways. They can be named after the causative microorganism (bacterial, viral, etc) as described above. They may be also be described anatomically. For example, if only one part, or lobe, of the lung is involved, it is referred to as ‘lobar pneumonia.’ ‘Multilobar’ pneumonia involves more than one lobe, and is often more severe. ‘Bronchial’ pneumonia affects the lungs in a widespread manner with patches seen on x-ray throughout both lungs. ‘Interstitial’ pneumonia involves the areas in between the alveoli and may also be called ‘interstitial pneumonitis.’ 

The combined clinical classification, now the most commonly used classification scheme, attempts to identify a person's risk factors when he or she first comes to medical attention. The advantage of this classification scheme over previous systems is that it can help guide the selection of appropriate initial treatments even before the microbiologic cause of the pneumonia is known.

There are two broad categories of pneumonia in this scheme: community-acquired pneumonia and hospital-acquired pneumonia.

• Community-acquired pneumonia (CAP) is infectious pneumonia in a person who has not recently been hospitalized. CAP is the most common type of pneumonia. The most common causes of CAP vary depending on a person's age, but they include Streptococcus pneumoniae, viruses, the atypical bacteria, and Haemophilus influenzae. Overall, Streptococcus pneumoniae (pneumococcal pneumonia) is the most common cause of community-acquired pneumonia worldwide.
   
• Hospital-acquired pneumonia, also called nosocomial pneumonia, is pneumonia acquired during or after hospitalisation for another illness or procedure with onset at least 72 hours after admission. The causes, microbiology, treatment and prognosis are different from those of community-acquired pneumonia. Up to 5% of patients admitted to a hospital for other causes subsequently develop pneumonia. Hospitalised patients may have many risk factors for pneumonia, including mechanical ventilation, prolonged malnutrition, underlying heart and lung diseases, decreased amounts of stomach acid, and immune disturbances. Additionally, the microorganisms a person is exposed to in a hospital are often different from those at home.

Hospital-acquired microorganisms may include antibiotic-resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, Klebsiella, Enterobacter, and Serratia. Because individuals with hospital-acquired pneumonia usually have underlying illnesses and are exposed to more dangerous bacteria, the pneumonia tends to be more deadly than community-acquired pneumonia.

Treating Pneumonia 

Bacterial pneumonia

Antibiotics are used to treat bacterial pneumonia. The choice of antibiotic should ideally be based on the causative microorganism and its known antibiotic sensitivity.

However, a specific cause for pneumonia is identified in only 50% of people, even after extensive evaluation.

Because treatment should generally not be delayed in any person with a serious pneumonia, empiric treatment is usually started well before laboratory reports are in. 

Community-acquired pneumonia

In North America, where the "atypical" forms of community-acquired pneumonia are becoming more common, macrolides (such as azithromycin and clarithromycin), the fluoroquinolones, and doxycycline have displaced amoxicillin as first-line outpatient treatment for community-acquired pneumonia. The duration of treatment has traditionally been seven to ten days, but there is increasing evidence that shorter courses (as short as three days) are sufficient.

Hospital-acquired pneumonia

Antibiotics for hospital-acquired pneumonia include third- and fourth-generation cephalosporins, carbapenems, fluoroquinolones, aminoglycosides, and vancomycin.

These antibiotics are usually given intravenously. Multiple antibiotics may be administered in combination in an attempt to treat all of the possible causative microorganisms. Antibiotic choices vary from hospital to hospital because of regional differences in the most likely microorganisms, and because of differences in the microorganisms' abilities to resist various antibiotic treatments.15 People who have difficulty breathing due to pneumonia may require extra oxygen. Extremely sick individuals may require intensive care, often including endotracheal intubation and artificial ventilation.

Viral pneumonia

Viral pneumonia caused by influenza A may be treated with rimantadine or amantadine, while viral pneumonia caused by influenza A or B may be treated with oseltamivir or zanamivir. These treatments are beneficial only if they are started within 48 hours of the onset of symptoms. Many strains of H5N1 influenza A, also known as avian influenza or "bird flu," have shown resistance to rimantadine and amantadine. There are no known effective treatments for viral pneumonias caused by the SARS coronavirus, adenovirus, hantavirus, or parainfluenza virus.

Prognosis for Pneumonia

The death rate (or mortality) also depends on the underlying cause of the pneumonia. Pneumonia caused by mycoplasma, for instance, is associated with little mortality. However, about half of the people who develop methicillin-resistant Staphylococcus aureus (MRSA) pneumonia while on a ventilator will die. In regions of the world without advanced health care systems, pneumonia is even deadlier. Limited access to clinics and hospitals, limited access to x-rays, limited antibiotic choices, and inability to treat underlying conditions inevitably leads to higher rates of death from pneumonia. For these reasons, the majority of deaths in children under five due to pneumococcal disease occur in developing countries.

Preventing Pneumonia

A vaccine called Pneumovax is available in Australia that can help prevent pneumonia due to the pneumococcus bacterium (pneumococcal pneumonia). It is usually given to those most at risk such as the over-65s, people whose immune systems are impaired, Aboriginal and Torres Strait Islander people over 50 years of age, and people with chronic illness that would put them at high risk if they contracted pneumococcal pneumonia.

Another pneumococcal vaccine (Prevenar) is recommended for all Australian children to prevent pneumonia and other pneumococcal infections. According to the National Centre for Immunisation Research and Surveillance, pneumococcal disease rates declined significantly after 2004 when a universal pneumococcal vaccine program was instituted for young children. Pneumococcal disease notification rates, Australia, 2002 to 2007,* by age group and year of diagnosis.

A flu vaccination (e.g. Fluvax, Fluarix or Vaxigrip) every year before winter comes is a sensible precaution for those at risk of flu. Pneumonia can be a complication of flu in people who are immunocompromised (e.g. whose immune systems are suppressed by drugs or medical conditions) or who are not in optimal health.

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