Pneumonia: Symptoms, Causes, Treatment

Pneumonia is an infectious disease of the lungs. In this disease sacs of one or both lungs get infected. The infected lungs sacs may be filled with pus or fluid thereby causing cough with pus or phlegm, difficulty in breathing, chill, and fever. The disease has been caused by various organisms including bacteria, viruses, parasites, and fungi.
Pneumonia ranges from mild illness to life-threatening disease. It is dangerous for infants, young children, and people with age more than 65 years, and individuals that have weak immune systems or with other health problems. 
According to UNICEF (United Nation International Children Emergency Fund), the mortality of children due to pneumonia is more than any other illness and about one million children of age 2-5 died every year in the world.

Signs and Symptoms

The symptoms and signs of pneumonia vary depends on the range of seriousness of the disease, type of disease-causing organism, overall health, and age of an individual. As a whole, pneumonia has the following symptoms

  • Fever, shaking chills and sweating
  • Lower than normal body temperature in aged persons and persons having a weak immune system.
  • Difficulty in breathing
  • Chest pain during coughing and breathing
  • Diarrhea, nausea, or vomiting
  • Fatigue
  • Weakness
  • Confusion or change in mental state in aged persons.
  • Cough with phlegm.
  • In a few cases, newly born children and infants do not show signs of pneumonia. But the children of age 2-5 may show the symptoms.


The disease is caused by various germs including viruses and bacteria, present in the air that breathed in by individuals. Usually, the body prevents these germs to attack the internal organs. But when the body’s immune system is weak, these germs attack the lungs and cause the disease.


Most types of bacteria are responsible for causing pneumonia.

  • Staphylococcus aureus is gram-positive cocci and causes pneumonia, its infection spreads from the blood to the lungs. 
  • Streptococcus pneumonia is gram-positive cocci and responsible for causing lobular pneumonia.
  • Klebsiella pneumonia is a gram-negative, non-motile, facultative anaerobic microorganism and responsible for causing pneumonia.
  • Streptococcus pyogenes causes typical pneumonia.
  • Streptococcus agalactiae mostly causes pneumonia in neonates.
  • Mycoplasma pneumoniae is a bacterial microorganism and causes pneumonia but pneumonia caused by this microorganism is less severe than caused by other organisms.
  • Mycobacterium tuberculosis is also responsible for causing a severe form of lung infection.
  • Legionella pneumophila and Legionella micdadei are the most common cause of pneumonia in humans.
  • Chlamydia pneumoniae may cause a mild or severe form of lung infection.
  • Pseudomonas aeroginosa and the other species of Pseudomonas cause pneumonia, especially Pseudomonas aeroginosa causes ventilator-associated pneumonia or hospital-acquired pneumonia.
  • Acinetobacter species also mostly cause hospital-acquired pneumonia.


Most fungi are also responsible for causing lungs infection in humans. Most humans get the fungal lung infection when they inhaled spores of fungi through dust and spores are present in soil and bird’s droppings, 

  • Histoplasma capsulatum causes an infection in the lungs when inhaled by a person. It causes a severe form of lung infection in adults, infants, immunocompromised, and AIDS patients. It typically causes flask shape ulcers.
  • Blastomyces dermatitis sometimes causes only the infection of the upper respiratory tract but also causes chronic pneumonia.
  • Some opportunistic fungi also cause lungs infection like species of Candida, Cryptococcus, and Aspergillus. They cause severe lung infection in immunocompromised patients.


Viruses are mostly responsible for causing flu and cold in humans and the symptoms of viral pneumonia are the same as that of infection caused by Influenza virus-like coughing, headache, weakness, and fever. But some viruses cause severe respiratory tract problems. Such as Covid-19 (Coronavirus) causes severe pneumonia in humans, Respiratory syncytial virus (RSV), Influenza virus, Adenovirus, Picornaviruses, Human metapneumovirus, and varicella-zoster virus also cause pneumonia in humans.
It is estimated that about 100 million cases of viral pneumonia are reported each year.


Parasites like Toxoplasma gondi, Ascaris lumbricoid cause pneumonia in humans. But mostly parasites cause pneumonia in immunocompromised patients. 

Is pneumonia contagious?

All the microorganisms responsible for causing pneumonia are contagious. They can spread from one person to another person. A person can acquire the microorganism causing pneumonia by inhaling the aerosols when an infected person coughs, sneezes, yawns, or talks. 
But the fungal pneumonia is not contagious, a person can get this infection by inhaling the organism or spores of fungi from the environment.

Types of Pneumonia 

Pneumonia disease is classified on two bases: one is the type of germ, and the other is the place where one gets the infection.

Community drive pneumonia 

It is the most common type of pneumonia. Individuals get this type of infection outside the hospital and other health care facilities environment. It is caused by bacteria, fungi, and viruses.

Hospital-acquired pneumonia 

This type of pneumonia is caused by the germs present in a hospital. Hospital-acquired pneumonia is more severe, because the germs in the hospital environment are more resistant to antibiotics, and the people in the hospital are already ill such as the species of Pseudomonas and Acinetobacter. The infection which a person gets from the hospital is called nosocomial infection

Health-care acquired pneumonia

A person acquired this form of pneumonia when she/he stays in a health care unit or hospital for a longer period of time or due to the interaction with the patients.

Aspiration pneumonia

It happens when one inhales food, drink, saliva, and vomits into the lungs. It can also occur due to swallowing problems, brain injury, and excessive intake of alcohol and drug.

Ventilator-associated pneumonia

Most of the patients in the ICU acquired the infection from the contaminated pieces of equipment of the hospital. Most important is the Pseudomonas aeroginosa which causes ventilator-associated pneumonia in hospitalized patients.

Risk factors of pneumonia 

Pneumonia can affect anyone. But children and aged people are more at risk. Other risk factors include being hospitalized, having chronic illnesses, drug addiction, alcohol consumption, taking immunosuppressive drugs such as steroids, weak immune system, and people who already have other infections like flu, cold, diabetes, heart problems, and asthma.
Sometimes environmental factors also increase the risk of pneumonia-like pollution, gases in the air, and chemicals.

Stages of pneumonia


This is the first stage which occurs in the initial 24 hours of pneumonia. In this stage bacteria or any other specific microorganism starts multiplying in the alveoli and causes the congestion of capillaries in the alveolar walls. Specific symptoms of this stage are coughing and difficulty in breathing.

Red Hepatization:

This stage comes after the congestion. In this stage capillaries of alveoli are inflamed with blood. Color of lungs become red resembles with liver and alveoli accumulated with more erythrocytes, neutrophils, and epithelial cells.

Grey Hepatization:

In this stage, the color of the lungs appears as yellow or grey-brown due to the breakdown of a large number of RBCs in the infected area.


In this stage, complete recovery of lungs occurs due to the ingestion of debris by macrophages.


The infection could result in complications in some people that are at high risk including the entrance of bacteria in the bloodstream causing bacteremia, difficulty in breathing, accumulation of fluid in lungs and pus formation in the cavities of the lungs called lungs abscess which can be treated with antibiotics or can be removed by surgery.

Walking pneumonia

Walking pneumonia is a milder form of pneumonia even a person having this type of pneumonia does not know that she/he has pneumonia. Symptoms of walking pneumonia are coughing mild fever and weakness.


For the treatment of bacterial pneumonia and fungal pneumonia, doctors prescribe antibacterial drugs and antifungal drugs respectively. In the case of viral pneumonia as antiviral drugs are not available patient can recover in a few days.


Pneumonia can be prevented by:

  • Vaccination- Pneumonia, and flu can be prevented by some available vaccines. Doctor review must be consulted before taking vaccines, as vaccine guidelines have been changed with time. Children vaccination must also be insured to save infants and early age children from the infection. Available vaccines of pneumonia are Prevnar 13 and Pneumovax 23.

Prevnar 13: 

this vaccine is effective against the 13 different types of bacteria causing pneumonia and according to the CDC this vaccine can be used by people age about 2-65. 

Pneumovax 23: 

this vaccine is effective against 23 different types of bacteria causing pneumonia.

  • Strengthen the immune system by taking proper diet and doing exercise.
  • Avoid smoking, alcohol, and drugs.
  • Practicing good hygienic conditions (washing of hands properly).
  • Cover the mouth while coughing and sneezing.

Diagnosis of pneumonia

First, the patient with typical signs and symptoms has to consult the doctor and the doctor will ask questions about the medical history of a patient and may ask for the tests. Diagnostic tests for pneumonia are:

Chest X-ray

It tells about the inflammations in the and through x-ray doctor will come to know about the site of infection in the lungs.

Blood culture

This test is used for the confirmation of the lung infection.

Sputum culture

In this test, sputum is taken as a sample and then cultured to identify the microorganism causing infection.

CT scan

It provides a clear picture of the lungs.     


Pneumonia is an infection of the lungs and can be caused by bacteria, viruses, and fungi. Signs and symptoms of pneumonia can be milder or severe depending on its type, age, and health of the patients. It is a contagious disease and can be prevented by taking precautionary measures.

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