Overview on Pathophysiology of Pneumonia
Krushna K. Zambare*1, Avinash B. Thalkari1
SBSPM’s B. Pharmacy College, Ambajogai – 431517. Dist. Beed. Maharashtra.

*Corresponding Author E-mail: krushnazambare1@gmail.com



Pneumonia is an infection in one or both lungs. It is caused by bacteria, viruses, or fungi etc. In greek language "pneumon" means "lung," so the word "penumonia" means "lung disease. With pneumonia, the lungs may fill with fluid or pus. The pneumonia can be life-threatening to anyone, but predominantly infants, children and people over 65 are at higher risk. Pneumonia symptoms may vary from so milder to severe that hospitalization is required. Patients with pneumonia should get medical attention to prevent the complications and health hazards. Proper treatment and care of pneumonia patient can prevent the morbidity and mortality associated with it.


KEYWORDS: Pneumonia, Community acquired pneumonia, Streptococcus pneumonia, chronic pneumonia.




Pneumonia is an inflammation of lung primarily affecting the air sacs called alveoli or interstitial spaces.1 In greek language "pneumon" means "lung," so the word "penumonia" means "lung disease."2 Peoples of all ages are affected by this disease but occur more severe in older adults, babies, and people with other disorders can become very ill.3 Pneumonia causes the morbidity and mortality in HIV infected patients4.



Pneumonia is classified in various ways some of which are as follows,

1.    By site acquired

a)    Community acquired pneumonia

b)    Hospital acquired pneumonia

2.    Clinically

3.    Area of lung infected

4.    Other


1.      By site acquired:

These pneumonias are acquired by the location and further classified into the following classes,

a)    Community acquired pneumonia (CAP):

It is acquired infectiously from normal social contact with peoples. Most commonly the peoples are affected by this disorder. It is mainly caused by bacteria or viruses such as Streptococcus pneumonia, Haemophilus influenza, Staphylococcus aureus, Moraxella catarrhalis, Klebsiella pneumonia, Pseudomonas aeruginosa, Legionella pneumophila. These bacteria and viruses mainly causes the inflammation of the upper respiratory tract. The severity and the extent of disease depend on host immunity, illness, causative organism, and age. The problems associated with it are difficulty breathing, fever, chest pains, and a cough.3,5,6,7


b)   Hospital acquired pneumonias:

It is acquired due to before or after hospitalization of individual for the any other disease. Hospital acquired microorganisms mainly Enteric Gram-negative organisms Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus are important causative agents for the disease. The patients with mechanical ventilation, prolonged malnutrition or antibiotic therapy, immunocompromised patient, underlying lung and heart diseases, decreased gastric acid are at higher risk of acquiring pneumonia. 3,5,6,7


2.    Clinically: It is classified in two types

a)    Acute pneumonia:

It is an inflammation of the alveoli and interstitial tissues of the lungs by an infectious agent resulting in acute respiratory symptoms and signs. People with acute pneumonia usually have symptoms that appear very quickly. Primarily viruses and bacteria’s are responsible for the acute pneumonia such as Streptococcus pneumoniae, Mycoplasma pneumoniae or Chlamydia pneumoniae. Symptoms of acute pneumonia may include fatigue, body aches, and chills. Acute Pneumonia develops quickly and usually lasts less than three weeks.7

b)   Chronic pneumonia:

Chronic pneumonia is an inflammation of the lungs that persists for longer duration of time, without a sudden onset. It is caused by mycobacteria, fungi, or bacteria which mainly include Nocardia, Actinomyces, Blastomyces dermatitidis, Mycobacterium tuberculosis, Coccidioides immitis, Histoplasma capsulatum that colonize the lungs and cause irritation. Signs of chronic pneumonia can include coughing, difficulty breathing, fever, wheezing, fatigue, night sweats, and chest pains.7


3.    Area of lung infected:

The part of the lung tissue affected is the another way for classifiying pneumonia. Commonly it is classified as follows,

a)    Lobar pneumonia:

Lobar Pneumonia is inflammation or infection of lungs and involves large portion of a lobe or an entire lobe of the lung. It is primarily affecting the young, adults, and infants. It is more commonly occur in men than in women. The disorder is mainly caused by microorganisms Streptococcus pneumoniae, Staphylococcus aureus, H. influenza, Klebsiella pneumoniae, Pseudomonas, Proteus, E. coli etc.  It is characterized by severe fever, dyspnea, debility and even loss of consciousness.7,8

b)   Lobular Pneumonia:

Also known as Bronchopneumonia. It is the acute inflammation and infection of the terminal bronchioles. Commonly it shows multiple foci of isolated, acute patchy consolidation, affecting one or more lobules of lung. These lesions are 1–4 cm in diameter, grey-yellow, dry, often centred on a terminal bronchiole wall. Symptoms include cough with mucus, chills, fever, chest pain, sweating, rapid breathing and shortness of breath.7,8


4.    Others: these include following types

a)    Aspiration pneumonia:

The inhalation of either foreign material into the bronchial tract leads to aspiration pneumonia. It is caused due to aspiration of oral or gastric contents at the time of eating, or after reflux or vomiting into bronchi. This may result in to infection of lung as aspirated material may contain the bacteria.  Sometimes aspiration may leads to death of the person. Aspiration of lipid content like liquid paraffin may lead to lipid pneumonia.3,6,7,8

b)   Chemical pneumonia:

It may be caused by inhalation of fumes of toxic chemicals such as pesticides.7

c)    Immunocompromised people pneumonia:

The persons mainly on the anticancer, corticosteroid therapy or with AIDS are more likely to get these type of pneumonias. Some microorganisms are also responsible for this disease which are cytomegalovirus, invasive aspergillosis and candidiasis, Pneumocystis jiroveci, Mycobacterium avium-intracellulare.7

d)   Severe acute respiratory syndrome (SARS):

It is deadly disease mainly caused by coronaviruses which infects respiratory tract. Symptoms include shortness of breath, tachypnea, and pleurisy.7

e)    Necrotizing pneumonia:

Necrosis of the pulmonary cells may leads to necrotizing pneumonia. Sometimes it may result in lung abscess. Commonly it caused by Mycobacterium tuberculosis, Staphylococcus aureus, Haemophilus influenzae, Klebsiella pneumoniae, Streptococcus pyogenes, Pneumococcus type III, Pseudomonas, adenovirus, influenza virus, human immunodeficiency virus (HIV), and Aspergillus species etc.7



As described previously different types of pneumonias have different causes. Generally some conditions and risk factors are important for causing the pneumonia such as smoking, alcoholism, COPD, liver disease, kidney disease, immunodeficiency etc. Some medications are also necessary for the generation of pneumonia which are proton pump inhibitors and histamine H-2 blockers. Microorganisms are the main causative agents of the pneumonias which are illustrated below,


Various viruses are responsible for causing pneumonia like rhinovirus, influenza virus, adenovirus, Herpes simplex virus, coronavirus, and cytomegalovirus.


Generally different forms of bacteria’s are the most leading cause of pneumonias eg. Mycoplasma pneumoniae, Staphylococcus aureus, Moraxella catarrhalis, Legionella pneumophilaHaemophilus influenzae, Chlamydophila pneumoniae.


Lung can also be affected by some of the fungal classes which may include  Histoplasma capsulatum, Cryptococcus neoformans, Pneumocystis jiroveci, and Coccidioides immitis.


Some parasites are also causing pneumonia eg. Toxoplasma gondii, Strongyloides stercoralis, Ascaris lumbricoides, and Plasmodium malariae.2,5,6,7,8,9



Ÿ  Variety of organisms leads to infection of the lungs leading to the different forms of pneumonia. Commonly the upper respiratory tract infection or infection to the other organs of body may lead to the infection of lower respiratory tract.

Ÿ  Bacteria gain the entry inside the lungs via haematogenous route if other organs of body are infected with them, through aspiration of contaminated food from gastrointestinal tract, or may be via inhalation. Viruses and the parasites enter the lung through the mouth, nose or skin.

Ÿ  After invading the lungs, bacteria’s or viruses proliferate and infect the parenchyma of lungs leading death of the lung parenchyma via apoptosis, this leads to the activation of immune system.

Ÿ  As a result the neutrophils, lymphocyte get activated and infiltrated into the alveoli, destroying the invading organisms and release the inflammatory mediators like cytokines, prostaglandin etc.

Ÿ  These inflammatory mediators cause the vasodilation which leads to the increased permeability resulting into accumulation of fluid in alveoli (edema).

Ÿ  The neutrophils, lymphocytes, invading organism, and fluid filled alveoli interrupt normal gaseous transportation in the lungs leading to pneumonia.10,11,12



Fig.1. Pathogenesis of pneumonia


Ÿ  Viral pneumonia tends to develop slowly over a number of days, whereas bacterial pneumonia generally develops rapidly, frequently over a day.

Ÿ  Patients of pneumonia generally show productive cough, fever, shortness of breath, chest pain during deep breaths, fever, confusion, and an increased rate of respiration.

Ÿ  Fever is not specific symptom as it may appear with other illnesses. Inflammation, white blood infiltration, purulent sputum, muscular aches, fatigue, nausea, vomiting, may also be seen in pneumonias.

Ÿ  In severe cases the symptoms include cyanosis, decreased thirst, convulsions, persistent vomiting, or decreased level of consciousness, increased heard rate etc.3,5,6


Fig.2. Symptoms of pneumonia



1)    Medical history and physical examination:

Physician may examine the chest with the stethoscope to listen coarse breathing, wheezing, crackling sounds and reduced breathing sounds in specific parts of lung which may indicate presence of pneumonia. Sometimes low blood pressure, high heart rate, or low oxygen saturation may also be indicators of pneumonia.

2)    Chest radiography:

Exact Confirmation of pneumonia is typically done by using combination of physical signs and a chest X-ray. The radiologic examination shows airspace opacity, lobar consolidation or interstitial opacities. Commonly it is used to check area of lung affected by pneumonia.

3)    Blood test: 

In this test complete Blood Count is done to check white blood cells level, Arterial blood gases for checking oxygen level in blood, and sometimes serum electrolytes and C-reactive protein are also used for detecting the pneumonia. Additionally they are useful for identifying the infection in the blood.

4)    Sputum culture:

A sputum culture is carried out to find and identify the microorganism causing an infection leading to pneumonia. The test is having limited diagnostic value because they are easily contaminated with upper respiratory secretions. It is useful in extremely ill patients.

5)    Pulse oximetry:

Pulse oximetry very simple, cheap and non-invasive method to examine level of oxygenation in body as the oxygen level falls in the pneumonia. It detects the amount of haemoglobin that is saturated with oxygen. In this method a sensor device is positioned on a thin part of the patient's body, generally fingertip or earlobe, or in case of an infant, across a foot. The technique utilizes the light absorptive property of hemoglobin and the pulsating nature of arterial blood flow to determine the oxygenation level in the body.  

6)    Computed tomography (CT) scan:

A CT scan can give additional details of the lungs and detect pneumonia that may be more difficult to see on a plain x-ray. It shows the airway in detail and help to determine if pneumonia is due to problem within the airway. It also shows the complications associated with pneumonia like abscesses or pleural effusions and enlarged lymph nodes.

7)    Ultrasound of the chest:

Ultrasound of lung is done if fluid surrounding the lungs is suspected. It shows amount of fluid is present and infection to the lungs.

8)    Needle biopsy of the lung:

Physician may sometime perform biopsy of lung to check the cause of pneumonia. This involves removing several small samples of lung and investigating them. Biopsies can be done using x-ray, CT, ultrasound and/or MRI.

9)    Pleural fluid culture:

The test is useful to determine the cause of lung infection. In this test the fluid is withdrawn from pleural area and examined to see if this fluid contains any bacteria, viruses, or fungi. This procedure is commonly called thoracentesis.

10) Bronchoscopy:

Bronchoscopy is used to look into the lungs' airways, which would be performed using a tube which is inserted inside the airways. The test examines the patient’s lungs, airways, vocal cord, and trachea. Bronchoscopy is a procedure that is performed to diagnose the cause of pneumonia.3,5,6,9,13



·      Non pharmacological therapy:

·      Drink ample of fluids to avoid dehydration and help loosen secretions and bring up phlegm.

·      Take plenty of rest to help body recover.

·      Cessation of Smoking also prevents the risk of pneumonia.



Pharmacological therapy:

·      Antibiotics:

Primarily these are used if the pneumonia is of bacterial origins such as amoxicillin, doxycycline, clarithromycin, Vancomycin, Fluoroquinolones, Minoglycosides.


·      Antiviral agents:

If the pneumonia is caused by viruses then antiviral drugs are useful which includes Oseltamivir, Zanamivir, Orperamivir, Rimantadine, Amantadine.


·      Vaccination:

To prevent the pneumonia infection the vaccination is important. Vaccination for influenza A and B are available.5,6,9,13



1.     https://www.mayoclinic.org/diseases-conditions/pneumonia/symptoms-causes/syc-20354204

2.     Sattar SBA, Sharma S. Bacterial Pneumonia. 2019; StatPearls Publishing.

3.     https://www.medicalnewstoday.com/articles/151632.php

4.     Feldman C. Pneumonia associated with HIV infection. Curr Opin Infect Dis. 2005; 18(2):165-70.

5.     https://www.webmd.com/lung/pneumonia-types#1

6.     https://www.mayoclinic.org/diseases-conditions/pneumonia/symptoms-causes/syc-20354204.

7.     Dunn L. Pneumonia: classification, diagnosis and nursing management. Nurs Stand. 2005; 19 (42): 50–4.

8.     Bodhankar SL, Vyawahare NS. A textbook of Pathophysiology. Nirali Prakashan, Sixth edition 2008, pp 4.9-4.10.

9.     Ramya Chellammal M. Bacterial Pneumonia. Research J. Pharm. and Tech. 2014; 7(8): 942-945.

10.   Alcón A, Fàbregas N. Torres A Pathophysiology of pneumonia. Clin Chest Med 2005; 26(1): 39-46.

11.   https://www.slideshare.net/hasnahnoi/pneumonia-38313892

12.   https://www.britannica.com/science/pneumonia

13.   Ramya Chellammal M. Bacterial Pneumonia. Asian J. Nur. Edu. & Research 2014; 4(3): 317-320.






Received on 27.06.2019        Accepted on 21.07.2019

© Asian Pharma Press All Right Reserved

Asian J. Pharm. Res. 2019; 9(3):177-180.

DOI: 10.5958/2231-5691.2019.00028.5