Pneumonia is a common disease, which occurs in all age groups. However, pneumonia is the leading cause of death in elderly, people who are chronically and terminally ill, and children under five years old worldwide. It can result from a variety of causes, including infection with bacteria, viruses, fungi, or parasites, and chemical or physical injury to the lungs.
Pneumonia is an irregular inflammatory condition of the lung. It is often described as inflammation and abnormal fluid filling of the alveoli of the lung, which are microscopic air filled sacs in the lungs responsible for gas exchange. 2] Typical symptoms associated with pneumonia include cough, chest pain, fever, and difficulty in breathing. Diagnostic tools include x-rays and examination of the phlegm. Bacterial pneumonia is typically treated with antibiotics or antiviral drugs; therefore, treatment depends on the cause of pneumonia. There are vaccines available to prevent certain types of pneumonia. However, the prognosis depends on the type of pneumonia, the appropriate treatment, any complications, and the person’s underlying health.  Microorganisms, irritants and unknown causes, can cause pneumonia.
When pneumonias are grouped this way, infectious causes are the most common type. The symptoms of infectious pneumonia are caused by the infiltration of the lungs by microorganisms and by the immune system’s response to the infection. Only a few strains of microorganisms are responsible for most cases of pneumonia however, more than one hundred strains of microorganism can cause pneumonia. Viruses and bacteria are the most common causes of pneumonia. Fungi and parasites are less common causes of infectious pneumonia.  Viruses invade cells in order to reproduce.Usually, a virus reaches the lungs when viruses carried by the wind 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. Even more lung damage occurs when the immune system responds to the viral infection. This combination of cell destruction and fluid-filled alveoli interrupts the normal transportation of oxygen into the bloodstream.
Many viruses affect other organs, which disrupt many body functions as well as damaging the lungs. Viruses can also make the body more vulnerable to bacterial infections. Therefore, bacterial pneumonia often complicates viral pneumonia. Viruses such as influenza virus, respiratory syncytial virus (RSV), adenovirus, and metapneumovirus commonly cause viral pneumonia. A rare cause of pneumonia except in newborns is the Herpes simplex virus.
People with weakened immune systems are also at risk of pneumonia caused by cytomegalovirus. 1] Bacteria usually enter the lung when bacteria carried by the wind are inhaled, but can also reach the lung through the bloodstream when there is an infection in another part of the body. In parts of the upper respiratory tract, such as the nose, mouth and sinuses, and can easily be inhaled into the alveoli is where most bacteria live.
Once inside, bacteria may invade the spaces between cells and between alveoli through connecting the pores. This invasion triggers the immune system to send a type of defensive white blood cell to the lungs.The defensive white blood cells engulf and kill the offending organisms, and release cytokines, which causes a general initiation of the immune system. This leads to the chills, fatigue, and fever, which are common in bacterial and fungal pneumonia.
The defensive white blood cells, bacteria, and fluid from surrounding blood vessels fill the alveoli and interrupt normal oxygen transport. Bacteria normally travel from an infected lung into the bloodstream, causing serious or even deadly disease such as septic shock, with low blood pressure and damage to multiple parts of the body including the brain, kidneys, and heart.Bacteria can also travel to the area between the lungs and the chest wall causing a complication where there is a buildup of pus around the lungs. The most common causes of bacterial pneumonia are Streptococcus pneumoniae and “atypical” bacteria. Atypical bacteria are parasitic bacteria that live inside the cell or do not have a cell wall. Furthermore, they cause generally less severe pneumonia, therefore atypical symptoms, and respond to different antibiotics than other bacteria. In the nose or mouth of many healthy people, you can find Gram-positive type bacteria that cause pneumonia.In developing countries, approximately one million children annually are killed by Streptococcus pnuemoniae.
Another important Gram-positive bacterium is Staphylococcus aureus, and Streptococcus agalactiae cause of pneumonia in newborn babies. Gram-negative bacteria cause pneumonia less often than gram-positive bacteria. Haemophilus influenzae, Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa and Moraxella catarrhalis are some of the gram-negative bacteria that cause pneumonia.
If vomit is inhaled, these bacteria may enter the lungs because t often lives in the stomach or intestines. Chlamydophila pneumoniae, Mycoplasma pneumoniae, and Legionella pneumophila are “atypical” bacteria, which cause pneumonia.  Fungal pneumonia is infrequent. However, individuals with immune system problems due to AIDS, immunosuppresive drugs, or other medical problems are vulnerable to fungal pneumonia. The pneumonia caused by fungi is similar to that of bacterial pneumonia. Histoplasma capsulatum, blastomyces, Cryptococcus neoformans, Pneumocystis jiroveci, and Coccidioides immitis are most often the cause of fungal pneumonia.In the Mississippi River basin, Histoplasma capsulatum is most commonly found, and Coccidioides immitis in the southwestern United States.
An assortment of parasites can affect the lungs. These parasites normally enter the body through the skin or by being swallowed. Once inside, they travel to the lungs, typically through the blood. Similar to other cases of pneumonia, a combination of cellular damage and immune response causes disruption of oxygen transportation. One type of white blood cell responds forcefully to parasite infection.
Eosinophils, the one type of white blood cells, in the lungs can lead to eosinophilic pneumonia, therefore complicating the primary parasitic pneumonia. Toxoplasma gondii, Strongyloides stercoralis, and Ascariasis are the most common parasites causing pneumonia.  Further investigations are needed to confirm the diagnosis, if pneumonia is suspected based on a patient’s symptoms and conclusions from physical examination. In some cases, information from a chest X-ray and blood tests are helpful, and phlegm cultures in some cases.The chest X-ray is normally used for diagnosis in hospitals and some clinics with X-ray facilities. Nevertheless, in a common practice, pneumonia is usually diagnosed based on symptoms and physical examination alone.
It can be very difficult to diagnose pneumonia in some people, especially those who have other illnesses. A chest CT scan or other tests may be needed to distinguish pneumonia from other illnesses occasionally.  There are numerous ways to prevent infectious pneumonia. Properly treating primary illnesses, such as AIDS, can lessen a person’s risk of pneumonia.
Termination of smoking is important not only because it helps to limit lung damage, but also because cigarette smoke interferes with numerous body’s natural resistance against pneumonia.  Research shows that there are numerous ways to prevent pneumonia in newborn infants. Pregnant women test for Group B Streptococcus and Chlamydia trachomatis, then giving antibiotic treatment if needed, reduces pneumonia in infants. By suctioning the mouth and throat of infants with meconium-stained amniotic fluid lessens the rate of aspiration pneumonia.
4] Vaccination is important for preventing pneumonia in both children and adults. Vaccinations in opposition to Haemophilus influenzae and Streptococcus pneumoniae within the first year of life have greatly abridged the role these bacteria play in causing pneumonia in children. Since, many adults obtain infections from children, vaccinating children against Streptococcus pneumoniae has also led to a decreased occurrence of these infections in adults. Now commonly used around the world is Hib vaccine.As of 2009 predominantly used in high-income countries is the childhood pneumococcal vaccine, even though this is changing. Rwanda became the first low-income country to initiate pneumococcal conjugate vaccine into their national immunization program in 2009.  A vaccine against Streptococcus pneumoniae is also available for adults.
It is at this time suggested for all healthy individuals older than 65 and any adults with emphysema, congestive heart failure, diabetes mellitus, and cirrhosis of the liver, alcoholism, cerebrospinal fluid leaks, or those who do not have a spleen in the United States.A repeat vaccination may also be required after five or ten years.  The same individuals who receive vaccination against Streptococcus pneumoniae should be given yearly influenza vaccines. In addition, health care workers, nursing home residents, and pregnant women should receive the vaccine as well. Medications such as amantadine, rimantadine, zanamivir, and oseltamivir can help prevent influenza when an influenza outbreak is occurring.
 In all parts of the world, pneumonia is a common illness.Among all age groups, it is a major cause of death. Many of pneumonia deaths occur in the newborn period in children.
The World Health Organization estimates that one in three newborn infant deaths is caused by pneumonia. Over two million children under five die each year worldwide. In addition, the World Health Organization assesses up to 1 million of these vaccine preventable deaths are caused by the bacteria, Streptococcus pneumoniae, and over 90% of these deaths take place in developing countries.Mortality from pneumonia generally lessens with age until late adulthood. However, elderly individuals are at meticulous risk for pneumonia and associated mortality.
Because of the very high burden and relatively low awareness of disease in developing and industrialized countries, the global health community has declared November 2 to be World Pneumonia Day, a day for concerned citizens and policy makers to take action against the disease.  Most types of bacterial pneumonia can be restored back to health within two to four weeks with treatment.Viral pneumonia may last longer, and mycoplasmal pneumonia may take four to six weeks to heal completely. The concluding result of an incidence of pneumonia depends on how sick the person is when he or she is first diagnosed.  About one of every twenty people with pneumococcal pneumonia dies in the United States. In cases where the pneumonia progresses to blood poisoning, just over 20% of victims die. The mortality rate depends on the primary 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 pneumonia while on a ventilator will die. In regions of the world without highly developed health care systems, pneumonia is even deadlier. Limited access to clinics and hospitals, x-rays, antibiotic choices, and inability to treat primary conditions unavoidably 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.
5] In the United Kingdom, the annual incidence of pneumonia is approximately six cases for every 1000 people for the 18–39 age groups. For those over 75 years of age, it increases to 75 cases for every 1000 people. Approximately, 20–40% of individuals who contract pneumonia requires hospitalization however, between 5–10% are admitted to an intensive care unit. Correspondingly, the mortality rate in the United Kingdom is around 5–10%.
 Pneumonia cases increases during the winter months than during other times of the year.Pneumonia occurs more commonly in males than females, and more often in African Americans than Caucasians due to differences in producing Vitamin D from sunlight. Individuals with primary illnesses such as Alzheimer’s disease, cystic fibrosis, emphysema, tobacco smoking, alcoholism, or immune system problems are at a higher risk for pneumonia. These individuals are also more likely to have repeated episodes of pneumonia.
People who are hospitalized for any reason are also at high risk for pneumonia.