According to a 2018 report released by Our World in Data, an online publication focusing on problems affecting the globe, pneumonia is a leading cause of death among children under five years of age globally. It also reveals that in 2017 alone, more than 809,000 children under five years lost their lives to this lung condition. 
Pneumonia is an inflammatory lung infection that primarily affects the alveoli (tiny air sacs in the lungs). The air sacs or alveoli may even get filled with fluid or pus, and the symptoms range from mild to severe. These prominent symptoms include cough with phlegm or pus, high fever, chills and breathing difficulties. Pneumonia, which can affect one or both the lungs, can be caused by viral or bacterial infections. Senior citizens (above 65 years of age), infants below two years, people with chronic lung conditions and severe infections are more vulnerable to pneumonia. This is because their immune systems are compromised. Also, lifestyle habits like smoking and alcoholism escalate your risk of catching this lung infection.
Based on the causative organism and the location of infection, pneumonia can be divided into the following types.
Community-Acquired Pneumonia (CAP)
This occurs when the individual has not visited a hospital or a health care facility recently and is further subdivided as follows.
- Bacteria – Streptococcus pneumoniae is the causative organism here. It commonly occurs after the flu and may affect a part of the lung leading to lobar pneumonia.
- Atypical pneumonia – Also called walking pneumonia, this type does not warrant bed rest and is less in severity. It may be caused by Mycoplasma or Chlamydia organisms.
- Fungi – This occurs in individuals with weak immune systems. The fungi found in soil or bird droppings is the causative factor.
- Viruses like COVID-19 – The viruses causing cold and flu may also cause pneumonia. This is commonly seen in children under five years of age. COVID-19 is seen to cause severe pneumonia.
This occurs within health care institutions. It includes Hospital-acquired pneumonia (HAP) and Ventilator-associated pneumonia (VAP)
This occurs due to inhalation of the vomit, mucus, certain chemicals or a foreign object. This inhalation results in inflammation of the bronchi and lungs. 
Consolidation, red hepatisation, grey hepatisation and resolution are the four stages of pneumonia. Their brief explanation is given below:
This stage occurs within the first 24 hours. Due to bacteria and fluid, the lungs become red, heavy and congested. A person experiences coughing and deep breathing during this stage.
This stage occurs around three days after the first stage. The lungs resemble the liver due to its red, firm and airless appearance. This stage is characterised by alveoli filled with erythrocytes, neutrophils, desquamated epithelial cells, and fibrin.
This is an avascular (no involvement of blood vessels) stage that occurs two to three days after the red hepatisation. In this stage, red blood cells collapse, which gives the lungs a greyish appearance. Lungs appear pale and dry. Fibrin and exudate (fluids consisting of cells and proteins which leak out from blood vessels into surrounding tissues) dominate this stage.
This stage is achieved when the pulmonary structure returns to normal. Enzymatic digestion of exudate occurs, which gets reabsorbed, coughed out or ingested by macrophages. The consolidate tissue gets re- aerated. Fluid infiltration may cause excess sputum.
Pneumonia mainly affects the lungs. The primary responsibility of the lungs is to oxygenate your blood and remove the excess carbon dioxide. For optimal functioning of the lungs, your airways (the bronchi) need to be open and clear. Any obstruction due to mucus will obstruct your airways, and this will lead to the symptoms of pneumonia.
Pneumonia is characterized by symptoms that include breathing issues, cough and high- grade fever. However, the signs and symptoms may differ based on age and the type of pneumonia you have as well as your overall health condition. Here, we guide you through some common manifestations.
- Pain in the chest, especially when you breathe or cough
- Phlegm or mucus- producing cough- the mucus may vary from yellow, greenish to even blood tinged.
- Extreme fatigue
- Loss of appetite
- Sweats and chills
- Nausea and vomiting
- Difficulty in breathing
Apart from these, kids and senior citizens may experience certain other symptoms of pneumonia. While children under five years of age may undergo manifestations like fast breathing or wheezing, infants may have no other symptoms other than vomiting, depleted energy levels, or difficulty in drinking or eating. Elderly people, on the other hand, may experience confusion, abnormally low body temperature, etc. 
CAUSES AND RISK FACTORS
Viruses, bacteria and fungi are the main culprits behind pneumonia. You are likely to catch this infection via droplets (loaded with these pathogens) which are emitted by an infected person as he coughs and sneezes. Contaminated fomites may also give you pneumonia. You can acquire this infection during a hospital stay while undergoing procedures related to ventilators, or from the people around you. The bacteria that are commonly responsible for this ailment are commonly known as Streptococcus pneumoniae and Mycoplasma pneumoniae. Respiratory viruses that could also be the culprits for pneumonia include influenza (flu), respiratory syncytial virus (RSV) and rhinoviruses (common cold). Additionally, fungi from the soil and bird droppings may also lead to pneumonia. Examples of these pathogens are Pneumocystis jirovecii, Cryptococcus species, Histoplasmosis species, etc.
High-risk groups for pneumonia are as follows:
- People above 65 years of age
- Malnourished patients
- People with existing lung problems like bronchiectasis, asthma or chronic obstructive pulmonary disease(emphysema)
- People with medical problems like diabetes, chronic kidney or heart disease
- People with a weak immune system due to HIV infection, organ transplant, chemotherapy, or long-term steroid use
- People who have had a recent upper respiratory tract viral infection, including influenza
- Stroke survivors
- People who have a problem in swallowing
- People with restricted mobility.
The best way to prevent pneumonia is through vaccination. Pneumococcal vaccine, PCV13 and Haemophilus Influenzae Type b (Hib) can protect you against bacterial pneumonia. A regular flu shot is recommended as well to safeguard you against pneumonia which often accompanies flu. Apart from vaccines, other infection control measures can be taken.
- Frequent hand-washing with soap and water or alcohol-based hand rubs can be effective.
- As pneumonia is spread by contact with infected respiratory secretions, people with pneumonia should limit face-to-face contact with uninfected family and friends.
- The mouth and nose should be covered while coughing or sneezing, and tissues should be disposed of immediately.
- Sneezing/coughing into the sleeve of one’s clothing (at the inner elbow) is another means of containing sprays of saliva and secretions and has the advantage of not contaminating the hands.
A review of medical history and physical examination are of priority to detect pneumonia. Lungs will make crackling, bubbling or rumbling sounds in case of pneumonia. On suspicion of pneumonia further tests may be advised.
- Blood tests: These may be recommended to diagnose an infection and its cause.
- Chest X-ray: It helps your physician detect the signs of inflammation in your lungs and figure out its exact location and extent.
- Sputum culture: In this diagnostic test, a sample of your mucus is sent to the lab in order to find the cause of infection.
- Pulse oximetry: This test tells your doctor about the efficiency of your lungs in moving oxygen through your bloodstream. A sensor placed on your fingers measures oxygen levels in your blood.
- CT scan: It allows your doctor to view your lungs more clearly, giving him a detailed picture.
- Fluid sample: Your physician will suggest this test if you have fluid in the pleural space of your chest. The aim is to figure out the cause of the infection. The fluid sample will be collected with the help of a needle placed between your ribs.
- Bronchoscopy: This imaging test is recommended for people with severe symptoms of pneumonia and those who fail to respond to medicines. It gives a clear picture of the airways to your doctor.
The line of treatment depends on the type of pneumonia you are suffering from. For bacterial pneumonia, your doctor will prescribe antibiotics. For viral form, he will suggest antiviral medications. Fungal pneumonia requires antifungal medications. Your physician may also prescribe cough medications to help you eliminate it. The infection will take long to recover.
Alongside your medicines, you will need to rest a lot and keep yourself sufficiently hydrated. In case of severe pneumonia, hospitalisation may be required. Hospital treatment may include intravenous antibiotics, respiratory therapies that involve administering drugs and breathing exercises, etc. You may also need oxygen therapy to increase its levels in your bloodstream. This therapy is carried out through a nasal tube, face mask, or ventilator. The severity of your condition will determine the device to be used.
Quit smoking because it can have a detrimental effect on your lungs.
Ensure adequate intake of vitamins including vitamin C rich foods like strawberries, papaya, broccoli and peas have proven beneficial in preventing and treating pneumonia.
Your diet should have sufficient minerals like zinc as these are useful in building immunity and preventing pneumonia.
PROGNOSIS AND COMPLICATIONS
The prognosis of an individual with pneumonia depends on three factors, viz age, existence of comorbidities and severity of disease, if any. For patients treated on an outpatient basis, mortality is less than 1%. For patients admitted in a ward, the mortality ranges from 5% to15% and from 20% to 50% for patients admitted in an ICU (Intensive care unit).
This lung infection may come with a host of other health complications. Here is a low-down on them.
- Septicshock and organ failure: This may occur if pneumonia-causing bacteria enter your bloodstream.
- Infection in fluid: In some cases of pneumonia, the fluid that builds up around the lungs and chest cavity may get infected.
Lung abscess: The pus that forms around your lungs can lead to an abscess.
1. Our World in Data2. Cleveland Clinic3. American Lung Association4. Winchester Hospital