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Pneumonia – Definition, incidence, etiology, types

Pneumonia is a common sickness, arises in all age groups, and is a top cause of death among the elderly and people who are persistently ill. Vaccines to put off specific types of pneumonia are accessible. The diagnosis for an individual rests on the kind of pneumonia, the proper treatment, any complications, and the person’s health. The discovery of sulpha drugs ,pencillin was pivotal in the treatment of pneumonia ,but still is related to significant morbidity and mortality


Pneumonia is a disease of the lungs and respiratory system in which the alveoli (microscopic air-filled sacs of the lung accountable for taking in oxygen from the environment) become swollen and inundated with fluid.


Acute respiratory illness accounts for 3.9 million young children dying globally. About 90% of these deaths are due to pneumonia ,in developed countries the incidence of pneumonia is as low as 3%to4% but in developing countries it is as high as 30%to 40%. It has been estimated that in India respiratory infections caused 9,87,000 deaths of which 9,69,000 were due to respiratory infections alone.


Normally the airway distal to the larynx is sterile because of protective defence mechanisms including filtration of the air ,humidification of the inspired air , epiglottis closure over the trachea, cough reflex, alveolar macrophages.

Factors predisposing to pneumonia: It is more likely to develop when defence mechanisms become insufficient or are overwhelmed by the virulence of infectious agent. So factors predisposing to pneumonia are

  1. Aging
  2. Air pollution
  3. Altered consciousness: alcoholism ,head injuries ,seizures ,anesthesia ,drug overdose, stroke
  4. Altered oropharangyl flora secondary to antibiotics
  5. Bed rest and prolonged immobility
  6. Chronic diseases: chronic lung disease ,diabetes, heart disease ,ESRD (End Stage Renal Disease)
  7. Debilitating illness
  8. HIV infection
  9. Immunosuppressive drugs e.g. steroids chemotherapy
  10. Inhalation of noxious substances
  11. Intestinal or gastric feedings
  12. Malnutrition
  13. Smoking
  14. Tracheal intubation
  15. URTI (Upper Respiratory Tract Infection)

Acquisition of the organisms

  1. Aspiration from the nasopharynx or oropharynx:  Many of the organisms are normal inhabitants of the healthy pharynx in healthy adults.
  2. Inhalation of microbes present in the air.
  3. Hematogenous spread from a primary infection elsewhere in the body e.g. staphylococcus aureus.



  1. LOBAR PNEUMONIA :If a substantial portion of one or more lobes is involved .
  2. BRONCHO PNEUMONIA: It is used to describe pneumonia that is distributed in a patchy fashion having originated in one or more localized areas with in the bronchi and extending to the adjacent surrounding lung parenchyma.

The most clinically effective way to classify pneumonia is




It is defined as a lower respiratory tract infection of a lung parenchyma with onset in the community or during the first two days of hospitalization. The number of pneumonia cases peak in winter. Smoking is the one of the factor. Organisms community implicated in CAD includes

  • S Pneumonia
  • Mycoplasm
  • Chlamydia
  • Viruses

It occurs 48 hrs or longer after hospital admission and not incubating at the time of hospitalization .

  1. Ventilator associated pneumonia(VAP) :- This refers to pneumonia that occurs more than 48 hrs to 72 hrs after endotracheal intubation .

This includes any patients with new onset pneumonia who

  • Hospitalized in any acute case for more than 2 or more days with in 90 days of the infection.
  • Resides in long term care facility .
  • Received any recent antibiotic therapy, chemotherapy or wound care with in past 30 days of the current infection.
  • Attended a hospital or hemodialysis clinic .

The microorganism responsible for HAP, VAP, HCAP are usually bacterial and rarely viral or fungal .Many of the organism enters the lung after aspiration of particles from the patient’s own oropharyngeal immune supportive therapy, general dyes and endotracheal aspiration are usually risky factors predisposing to pneumonia, which contaminated health care device and the general environment are identical source of pathogens.

3 .Aspiration Pneumonia 

Results from inhalation of foreign matters such as stomach contents, vomitus ,or food particles into the bronchi. It is more likely to occur in elderly or debilitated patients, those receiving nasogastric tube feedings, high prevalence in those with an impaired gag reflex , poor oral hygiene or a decreased level of consciousness.

Opportunistic pneumonia certain patients with altered immune response are highly susceptible to respiratory infections.

Individual at high risk includes

  1. Those who have severe protein calorie malnutrition.
  2. Those who have immune deficiencies.
  3. Those who have received transplantation and are on treatment with immunosuppressive drugs.
  4. Patients who are treated with radiation therapy, chemotherapy drugs, corticosteroids.

These individual have a variety of altered parameter , including altered B & T lymphocytes function, depressed bone marrow function, and reduced levels or function of neutrophills and macrophages.