Pneumonia is an inflammatory condition of the lung which can result from infection with particular bacteria, viruses or other organisms. It is characterised by lung parenchyma inflammation and the filling of the air-filled sacs of the lung (alveoli) with fluid resulting in a decrease in elasticity which leads to inefficient gas exchange. In excess of 5 million cases of infectious pneumonia are estimated to occur annually in the US resulting in more than 1 million hospitalizations. The onset of this condition is usually prompted following the weakening of an individual’s immune system, such as by a viral upper respiratory tract infection or following an incidence of influenza. It is a condition of particular concern in those over sixty five years of age, those with chronic immune disorders or young infants, all of whom have a reduced ability to combat infections.

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Almost half of all pneumonia cases originate bacterially. Some incidences of pneumonia are acquired by the inhalation of small droplets containing the organism or bacteria and these germs enter the air when the infected individual sneezes or coughs. In other circumstances the condition precipitates when bacteria or viruses that are present in the nose or mouth under normal conditions enter the lungs. However, if a person is weakened by an existing condition, severe pneumonia can develop. Along with classification based on the symptoms experienced, pneumonia can be categorized based on where or how the disease is contracted and can usually be divided into several subgroups which comprise hospital acquired pneumonia, community acquired pneumonia and aspiration pneumonia.

CAP can develop as a result of the attack unleashed by pathogenic microorganisms on the lung and the response of the immune system to the infection that ensues. S. pneumonia, H. influenza, C. pneumonia and M. pneumonia are the prevalent bacterial origins of the condition with S.pneumoniae presenting as the most frequent pathogen responsible following epidemiological studies (Luna et al., 2000). A relatively inoffensive form of pneumonia results that rarely involves hospitalization. In accordance with the guidelines developed by the American Thoracic Society for the management of CAP patients should be treated for the possibility of an atypical pathogen infection (Niederman et al., 2001). Organism-specific therapy may be possible in some patients depending on culture results. CAP is characterized by the presentation of a high fever, shaking chills and a cough with yellowish sputum which may be accompanied by chest pain. It can also cause shortness of breath which considerably impacts those with chronic lung conditions such as asthma and emphysema.

Hospital-acquired pneumonia (HAP) tends to be more severe than pneumonia acquired in the community mostly due to the fact that the organisms involved tend to be more aggressive and difficult to treat. Also, individuals in hospitals or care homes who contract this condition may often already have compromised immune systems and may not be able to fight off the infection. It remains the most frequent and severe nosocomial infection encountered in the ICU and the mortality incidence of patients with HAP is high (33% of unventilated patients) (Smith-Sims, 2001). The symptoms of HAP are usually the same as CAP in general. Early and suitable antibiotic therapy has been discovered to result in a decline in patient mortality rates in clinical studies due to this type of pneumonia. Patients diagnosed with nosocomial pneumonia are twice as likely to survive if in receipt of suitable antibiotic therapy, with the timing and adequacy of treatment being of crucial importance (Celis et al., 1988). Due to the fact that the timing of antibiotic therapy with respect to suspicion of pneumonia is an imperative factor affecting mortality and that HAP diagnosis remains elusive, initial empiric therapy appears to be best practice (Fiel, 2001).

An example of an additional type of pneumonia is aspiration pneumonia which is often described as the inhalation of foreign substances such as gastric matter into the lungs. This can lead toconditions such aspiration pneumonia and aspiration pneumonitis. Aspiration pneumonitis results from chemical injury due to the inhalation of sterile gastric materials whereas aspiration pneumonia is an infectious process resulting from inhalation of saliva which has been previously colonised by pathogenic bacteria (Marik, 2001). Factors that predispose an individual to aspiration pneumonia include a decreased level of consciousness, neurologic disorders, dysphagia and the aspiration of material in association with a tracheostomy (Finegold, 1991). Antimicrobial agents are the keystone of treatment and prolonged therapy is important in the prevention of relapse.

Viral pneumonia on the other hand can be caused by the influenza virus along with herpes or varicella, including those responsible for the outbreak of the common cold (adenoviruses). The two types of influenza virus, A and B, are characterised by respiratory complaints in conjunction with headaches, fever and muscle aches. Contracting herpes or varicella pneumonia is usually rare unless infection with the varicella zoster virus (chicken pox) occurs. Adenovirus originating pneumonia is frequently accompanied by common cold symptoms such as a runny nose and conjunctivitis. Viral pneumonia symptoms include muscle aches, tiredness, low grade fever and the presence of a cough with very little mucus It is rarely serious and usually does not require admittance to hospital. Medicines such as analgesics (to relieve chest pain) and acetaminophen (to reduce fever) may be given to alleviate symptoms however this particular type of pneumonia is resistant to treatment with antibiotics unlike its bacterial counterpart.

A vast range of diagnostic strategies are available to identify the presence of pneumonia in individuals. These include laboratory tests such as sputum examination, blood cultures or urinary antigen tests for the suspected bacterium involved. Chest X-rays are common diagnostic tools utilized and are helpful in the detection of complications of the condition also. The treatment for pneumonia can vary depending on the gravity of the symptoms and the category of pneumonia the patient has. Bacterial pneumonia requires the administration of an antibiotic, the choice of which is influenced by the age of the patient, chronic medical conditions they may have and the microorganism responsible for the infection. Macrolides are the most popular choice of antibiotic and are usually recommended in the treatment of CAP as they are effective against most microorganisms involved in this particular class of pneumonia. Trimethoprim and sulfamethoxazole may be administered if the patient has a history of COPD or smoking. These antibiotics are usually accompanied by anti-fever medications such as ibuprofen and occasionally a cough suppressant may be suggested.

There are fewer options in the treatment of viral pneumonia however as very few antiviral agents are available on the market. Acyclovir is efficacious in children with lung infections involving herpes simplex, herpes zoster or varicella varieties (Feldman, 1994). Ganciclovir has been successfully demonstrated in immunocompromised patients with conditions such as AIDS or transplant patients with CMV (cytomegalovirus) pneumonia (Reed et al., 1988).

The prognosis of pneumonia is quite good in patients without complications. To aid in the prevention of this condition, rigorous hygiene procedures should be followed in settings such as hospitals and nursing homes where there are individuals present with compromised immune systems. Also, smoking cessation should be encouraged in patients. Current research is underway to establish a more efficient treatment for this condition which will still eradicate the infectious microorganism and promote early defense but without the inflammatory tissue injury associated with sepsis (Cazzola et al., 2005).

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