Pneumonia is an inflammatory condition of the lung, especially of the alveoli (microscopic air sacs in the lungs) or when the lungs fill with fluid (called consolidation and exudation). There are many causes, of which infection is the most common. Infecting agents can be bacteria, viruses, fungi, or parasites. Chemical burns or physical injury to the lungs can also produce pneumonia.
Typical symptoms include cough, chest pain, fever, and difficulty in breathing. Diagnostic tools include x-rays and examination of the sputum. Treatment depends on the cause of pneumonia; bacterial pneumonia is treated with antibiotics.
Pneumonia is a common disease that occurs in all age groups. It is a leading cause of death among the young, the old, and the chronically ill. Vaccines to prevent certain types of pneumonia are available. The prognosis depends on the type of pneumonia, the treatment, any complications, and the person's underlying health.
People with infectious pneumonia often have a cough producing greenish or yellow sputum or phlegm and a high fever that may be accompanied by shaking chills. Shortness of breath is also common, as is sharp or stabbing chest pain during deep breaths or coughs. Less frequent symptoms of pneumonia include coughing up blood, headaches, sweaty and clammy skin, loss of appetite, fatigue, blueness of the skin, nausea, vomiting, mood swings, and joint pains or muscle aches. Some forms of pneumonia can cause specific symptoms. Pneumonia caused by Legionella may cause abdominal pain and diarrhea, while pneumonia caused by tuberculosis or Pneumocystis may cause only weight loss and night sweats. Symptoms in the elderly can include new or worsening confusion (delirium) or may experience unsteadiness, leading to falls. Infants with pneumonia may have many of the symptoms above, but in many cases they are simply sleepy or have a decreased appetite.
Physical examination may reveal signs of illness including fever or sometimes low body temperature, an increased respiratory rate, low blood pressure, a high heart rate, or a low oxygen saturation, which is the amount of oxygen in the blood as indicated by either pulse oximetry or blood gas analysis. Struggling to breathe, confusion, and blue-tinged skin are signs of a medical emergency.
Findings from physical examination of the lungs may be normal, but often show decreased expansion of the chest on the affected side. Harsher sounds from the larger airways transmitted through the inflamed lung are heard as bronchial breathing on auscultation with a stethoscope. Rales (or crackles) may be heard over the affected area during inspiration. Percussion may be dulled over the affected lung, and increased rather than decreased vocal resonance distinguishes pneumonia from a pleural effusion. Because some of these signs are subjective, physical examination alone is insufficient to diagnose or rule out pneumonia.
Pneumonia can be due to microorganisms, irritants or unknown causes. When pneumonias are grouped this way, infectious causes are the most common.
The symptoms of infectious pneumonia are caused by the invasion of the lungs by microorganisms and by the immune system's response to the infection. Although more than one hundred strains of microorganism can cause pneumonia, only a few are responsible for most cases. The most common causes of pneumonia are viruses and bacteria. Less common causes of infectious pneumonia are fungi and parasites.
Viruses have been found to account for between 18—28% of pneumonia in a few limited studies. Viruses invade cells in order to reproduce. Typically, a virus reaches the lungs when airborne droplets are inhaled through the mouth and nose. Once in the lungs, the virus invades the cells lining the airways and alveoli. This invasion often leads to cell death, either when the virus directly kills the cells, or through a type of cell controlled self-destruction called apoptosis. When the immune system responds to the viral infection, even more lung damage occurs. White blood cells, mainly lymphocytes, activate certain chemical cytokines which allow fluid to leak into the alveoli. This combination of cell destruction and fluid-filled alveoli interrupts the normal transportation of oxygen into the bloodstream.
As well as damaging the lungs, many viruses affect other organs and thus disrupt many body functions. Viruses can also make the body more susceptible to bacterial infections; for which reason bacterial pneumonia may complicate viral pneumonia.
Viral pneumonia is commonly caused by viruses such as influenza virus, respiratory syncytial virus (RSV), adenovirus, and parainfluenza. Herpes simplex virus is a rare cause of pneumonia except in newborns. People with weakened immune systems are also at risk of pneumonia caused by cytomegalovirus (CMV).
Bacteria are the most common cause of community acquired pneumonia with Streptococcus pneumoniae the most commonly isolated bacteria. Another important Gram-positive cause of pneumonia is Staphylococcus aureus, with Streptococcus agalactiae being an important cause of pneumonia in newborn babies. Gram-negative bacteria cause pneumonia less frequently than gram-positive bacteria. Some of the gram-negative bacteria that cause pneumonia include Haemophilus influenzae, Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa and Moraxella catarrhalis. These bacteria often live in the stomach or intestines and may enter the lungs if vomit is inhaled. "Atypical" bacteria which cause pneumonia include Chlamydophila pneumoniae, Mycoplasma pneumoniae, and Legionella pneumophila.
Bacteria typically enter the lung when airborne droplets are inhaled, but can also reach the lung through the bloodstream when there is an infection in another part of the body. Many bacteria live in parts of the upper respiratory tract, such as the nose, mouth and sinuses, and can easily be inhaled into the alveoli. Once inside, bacteria may invade the spaces between cells and between alveoli through connecting pores. This invasion triggers the immune system to send neutrophils, a type of defensive white blood cell, to the lungs. The neutrophils engulf and kill the offending organisms, and also release cytokines, causing a general activation of the immune system. This leads to the fever, chills, and fatigue common in bacterial and fungal pneumonia. The neutrophils, bacteria, and fluid from surrounding blood vessels fill the alveoli and interrupt normal oxygen transportation.
Fungal pneumonia
Fungal pneumonia is an infection of the lungs by fungi. It can be caused by either endemic or opportunistic fungi or a combination of both. Case mortality in fungal pneumonias can be as high as 90% in immunocompromised patients, though immunocompetent patients generally respond well to anti-fungal therapy.
Cause
Specific instances of fungal infections that can manifest with pulmonary involvement include:
- histoplasmosis, which has primary pulmonary lesions and hematogenous dissemination
- coccidioidomycosis, which begins with an often self-limited respiratory infection (also called "Valley fever" or "San Joaquin fever")
- pulmonary blastomycosis
- pneumocystis pneumonia, which typically occurs in immunocompromised people, especially AIDS
- sporotrichosis - primarily a lymphocutaneous disease, but can involve the lungs as well
- cryptococcosis - contracted through inhalation of soil contaminated with the yeast, it can manifest as a pulmonary infection and as a disseminated one
- aspergillosis, resulting in invasive pulmonary aspergillosis
- rarely, candidiasis has pulmonary manifestations in immunocompromised patients.
Diagnosis
Fungal pneumonia can be diagnosed in a number of ways. The simplest and cheapest method is to culture the fungus from a patient's respiratory fluids. However, such tests are not only insensitive but take time to develop which is a major drawback because studies have shown that slow diagnosis of fungal pneumonia is linked to high mortality ). Microscopy is another method but is also slow and imprecise. Supplementing these classical methods is the detection of antigens. This technique is significantly faster but can be less sensitive and specific than the classical methods.
A molecular test based on real-time PCR is also available from Myconostica. Relying on DNA detection, this is the most sensitive and specific test available for fungi but it is presently limited to detecting only pneumocystis jirovecii and aspergillus. fungi pneumonia also could be spread to one person to another in places such as dorms and can not be detected through a chest x-ray and may need hospital treatment if nessary.
Parasitic pneumonia
Parasitic pneumonia is an infection of the lungs by parasites. It is a rare cause of pneumonia, occurring almost exclusively in immunocompromised persons (persons with a weakened or absent immune system). This is a respiratory infection that may or may not be serious.
There are a variety of parasites which can affect the lungs. In general, these parasites enter the body through the skin or by being swallowed. Once inside the body, these parasites travel to the lungs, most often through the blood. There, a similar combination of cellular destruction and immune response causes disruption of oxygen transportation. Depending on the type of parasite, antibiotics can be prescribed.
The most common parasites involved:
- Ascariasis
- Schistosoma
- Toxoplasma gondii
Idiopathic interstitial pneumonia
In medicine, idiopathic interstitial pneumonia (IIP), is a term used for a type of diffuse parenchymal lung disease (DPLD), also called interstitial lung disease (ILD). There are seven distinct subtypes of IIP.
Classification can be complex, and the combined efforts of clinicians, radiologists, and pathologists can help in the generation of a more specific diagnosis.
If pneumonia is suspected on the basis of symptoms and findings from physical examination, further investigations are needed to confirm the diagnosis. Information from a chest X-ray and blood tests are helpful, and sputum cultures in some cases. The chest X-ray is typically used for diagnosis in hospitals and some clinics with X-ray facilities. However, in a community setting (general practice), pneumonia is usually diagnosed based on symptoms and physical examination alone. Diagnosing pneumonia can be difficult in some people, especially those who have other illnesses. Occasionally a chest CT scan or other tests may be needed to distinguish pneumonia from other illnesses.
Pneumonia can be classified in several ways, most commonly by where it was acquired (hospital verses community), but may also by the area of lung affected or by the causative organism. There is also a combined clinical classification, which combines factors such as age, risk factors for certain microorganisms, the presence of underlying lung disease or systemic disease, and whether the person has recently been hospitalized.
An important test for pneumonia in unclear situations is a chest x-ray. Chest x-rays can reveal areas of opacity (seen as white) which represent consolidation. Pneumonia is not always seen on x-rays, either because the disease is only in its initial stages, or because it involves a part of the lung not easily seen by x-ray. In some cases, chest CT (computed tomography) can reveal pneumonia that is not seen on chest x-ray. X-rays can be misleading, because other problems, like lung scarring and congestive heart failure, can mimic pneumonia on x-ray. Chest x-rays are also used to evaluate for complications of pneumonia (see below.)
If antibiotics fail to improve the patient's health, or if the health care provider has concerns about the diagnosis, a culture of the person's sputum may be requested. Sputum cultures generally take at least two to three days, so they are mainly used to confirm that the infection is sensitive to an antibiotic that has already been started. A blood sample may similarly be cultured to look for bacteria in the blood. Any bacteria identified are then tested to see which antibiotics will be most effective.
A complete blood count may show a high white blood cell count, indicating the presence of an infection or inflammation. In some people with immune system problems, the white blood cell count may appear deceptively normal. Blood tests may be used to evaluate kidney function (important when prescribing certain antibiotics) or to look for low blood sodium. Low blood sodium in pneumonia is thought to be due to extra anti-diuretic hormone produced when the lungs are diseased (SIADH). Specific blood serology tests for other bacteria (Mycoplasma, Legionella and Chlamydophila) and a urine test for Legionella antigen are available. Respiratory secretions can also be tested for the presence of viruses such as influenza, respiratory syncytial virus, and adenovirus. Liver function tests should be carried out to test for damage caused by sepsis.
There are several ways to prevent infectious pneumonia. Appropriately treating underlying illnesses (such as AIDS) can decrease a person's risk of pneumonia. Smoking cessation is important not only because it helps to limit lung damage, but also because cigarette smoke interferes with many of the body's natural defenses against pneumonia.
Research shows that there are several ways to prevent pneumonia in newborn infants. Testing pregnant women for Group B Streptococcus and Chlamydia trachomatis, and then giving antibiotic treatment if needed, reduces pneumonia in infants. Suctioning the mouth and throat of infants with meconium-stained amniotic fluid decreases the rate of aspiration pneumonia.
Vaccination is important for preventing pneumonia in both children and adults. Vaccinations against Haemophilus influenzae and Streptococcus pneumoniae in the first year of life have greatly reduced the role these bacteria play in causing pneumonia in children. Vaccinating children against Streptococcus pneumoniae has also led to a decreased incidence of these infections in adults because many adults acquire infections from children. Hib vaccine is now widely used around the globe. The childhood pneumococcal vaccine is still as of 2009 predominantly used in high-income countries, though this is changing. In 2009, Rwanda became the first low-income country to introduce pneumococcal conjugate vaccine into their national immunization program.
A vaccine against Streptococcus pneumoniae is also available for adults. In the U.S., it is currently recommended for all healthy individuals older than 65 and any adults with emphysema, congestive heart failure, diabetes mellitus, cirrhosis of the liver, alcoholism, cerebrospinal fluid leaks, or those who do not have a spleen. A repeat vaccination may also be required after five or ten years.
Influenza vaccines should be given yearly to the same individuals who receive vaccination against Streptococcus pneumoniae. In addition, health care workers, nursing home residents, and pregnant women should receive the vaccine. When an influenza outbreak is occurring, medications such as amantadine, rimantadine, zanamivir, and oseltamivir can help prevent influenza.
Antibiotics improve outcomes in those with bacterial pneumonia. Initially antibiotic choice depends on the characteristics of the person affected such as age, underlying health, and location the infection was acquired.
In the UK empiric treatment is usually with amoxicillin, erythromycin, or azithromycin for community-acquired pneumonia. In North America, where the "atypical" forms of community-acquired pneumonia are becoming more common, macrolides (such as azithromycin), and doxycycline have displaced amoxicillin as first-line outpatient treatment for community-acquired pneumonia. The use of fluoroquinolones in uncomplicated cases is discouraged due to concerns of side effects and resistance. The duration of treatment has traditionally been seven to ten days, but there is increasing evidence that short courses (three to five days) are equivalent. Antibiotics recommended for hospital-acquired pneumonia include third- and fourth-generation cephalosporins, carbapenems, fluoroquinolones, aminoglycosides, and vancomycin. These antibiotics are often given intravenously and may be used in combination.
With treatment, most types of bacterial pneumonia can be cleared within two to four weeks. Viral pneumonia may last longer, and mycoplasmal pneumonia may take four to six weeks to resolve completely. The eventual outcome of an episode of pneumonia depends on how ill the person is when he or she is first diagnosed.
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.
Adenovirus can cause severe necrotizing pneumonia in which all or part of a lung has increased translucency radiographically, which is called Swyer-James Syndrome. Severe adenovirus pneumonia also may result in bronchiolitis obliterans, a subacute inflammatory process in which the small airways are replaced by scar tissue, resulting in a reduction in lung volume and lung compliance. Sometimes pneumonia can lead to additional complications. Complications are more frequently associated with bacterial pneumonia than with viral pneumonia. The most important complications include respiratory and circulatory failure and pleural effusions, empyema or abscesses.
Pneumonia is a common illness in all parts of the world. It is a major cause of death among all age groups and is the leading cause of death in children in low income countries. In children, many of these deaths occur in the newborn period. The World Health Organization estimates that one in three newborn infant deaths are due to pneumonia. Globally, over two million children under five years of age die of pneumonia each year, with 90% of these in the developing world. Approximately half of these cases and deaths are theoretically preventable, being caused by the bacteria Streptococcus pneumoniae - an organism for which a safe and highly effective vaccine is available. Mortality from pneumonia generally decreases as the victim ages until late adulthood, with significant increases in mortality seen in the elderly.
In the United Kingdom, the annual incidence rate of pneumonia is approximately 6 cases per 1000 people in individuals aged 18–39 years. For those over 75 years of age, the incidence rate rises to 75 cases per 1000 people. Roughly 20–40% of individuals who contract pneumonia require hospital admission, with between 5–10% of these admitted to a critical care unit. The case fatality rate in the UK is around 5–10%. In the United States, community-acquired pneumonia affects 5.6 million people per year, and ranks 6th among leading causes of death.
More cases of pneumonia occur during the winter months than at other times of the year. Pneumonia occurs more commonly in males than in females, and more often among Blacks than Caucasians, partly due to quantitative differences in synthesizing Vitamin D after exposure to sunlight. Individuals with underlying chronic illnesses, such as Alzheimer's disease, cystic fibrosis, emphysema, and immune system problems as well as tobacco smokers, alcoholics, and individuals who are hospitalized for any reason, are at significantly increased risk of contracting, and having repeated bouts of, pneumonia.
