Pneumonia 101: Symptoms, Causes, Types, Stages & Treatment

Accounting for 20.7% of total deaths in 2019, pneumonia is a leading cause of death in Singapore, just behind cancer. Read on to learn more about this deadly disease in our comprehensive guide.

by Elaine Francis, R.N.

What is pneumonia?

Pneumonia is an infection in our lung or lungs which causes swelling of the delicate tissues of the lung. We may also talk about people having a ‘chest infection’ or lower respiratory tract infection (‘LRTI’), either of which may be pneumonia.

Pneumonia can become serious and can cause life-threatening complications such as sepsis or abscesses in the lung. Pneumonia may be caused by a virus, bacteria, occasionally a fungus. The body’s immune response to an infection causes inflammation of the tissues of the alveoli – the tiny sacs in the lungs where the gases are exchanged.

To understand pneumonia, it helps to understand how our lungs work.

How Our Lungs Work

The main function of our lungs is to get carbon dioxide out of our bloodstream so that we can breathe it out as a waste product, and to get oxygen – the chemical essential for the health of every part of our body – from the air into our bloodstream.

When we breathe, we draw in air through our nose and mouth. This air travels down our trachea or windpipe and into our lungs. The airways continue to branch off into each lobe, and then into further, smaller branches. At the end of each of the smallest branches are bundles of air sacs, called alveoli.

The alveoli are surrounded by a network of fine blood vessels. Blood that has delivered oxygen all around the body returns to the heart depleted of nutrients and is pumped into the fine vessels in the tissues of the lungs. It can then excrete carbon dioxide, and pick up oxygen then return to the heart where the oxygen-rich blood can be pumped around the body again. This cycle continues throughout our lives with every heartbeat. 

With every breath, we take in microbes – bacteria, viruses and fungal spores. Thankfully, our lungs have several lines of defence to ensure that these microbes don’t cause any serious problems. Some get stuck in the moisture and mucous of our nose and mouth and are filtered through the fine hairs inside our noses. Microscopic cells in the lining of our respiratory system then push these particles out of the system. Our lungs are also lined with fine mucous which act as a protective barrier and the immune system provides cells which identify and destroy any microbes that enter.

Sometimes, however, our body’s natural defence system is not enough. Certain microbes are particularly good at crossing those barriers. Some health conditions may also weaken our defence system and make it easier for this to happen. When there are enough microbes colonising our lung tissue, they start to affect our lung function. Our immune system responds, filling our tissues with fluids and the fighter cells of the immune system. This causes swelling or inflammation, restricting the amount of tissue that can be used for gas exchange.

When we have reduced lung function, our body finds it harder to get enough oxygen and to blow off enough carbon dioxide. Our bodies automatically try to compensate for this by increasing the heart rate and by breathing harder and faster. If our lung function is seriously impaired, we can develop a build-up of carbon dioxide in the body which develops into a condition called acidosis, where our blood is literally more acidic than is healthy. Our kidneys will then try to compensate for this, which then affects the function of every essential organ in the body. This systemic, whole-body, response is known as sepsis and can be deadly.

What causes pneumonia?

Pneumonia is an infection caused by a microbe or ‘germ’. This microbe can be:

  • Bacterial: There are several types of bacteria that can cause pneumonia. Most community-acquired pneumonia and all aspiration pneumonia are caused by bacteria. Bacterial pneumonia can usually be well treated with a course of antibiotics.
  • Viral: The most common type of virus that causes pneumonia in adults is the influenza virus or ‘flu’. Viruses are not affected by antibiotics. In children, pneumonia is commonly caused by a virus called ‘RSV’.
  • Fungal: Pneumonia can also develop from an infection caught by breathing in the spores of certain types of fungus. This is less common, but when it does occur, it tends to happen in people who already have a compromised immune system.

Is pneumonia contagious?

The microbes that cause pneumonia can be passed from person to person, especially those that cause viral pneumonia. Some microbes can be passed from other animals to humans as well. Bacteria can also be introduced to the lungs when someone accidentally inhales food or fluids. These microbes can cause lung infections. 

However, it is important to note that exposure to the microbes that may cause pneumonia does not necessarily mean that you will get ill, and if you do get ill, it may not necessarily become pneumonia. Sometimes our natural immune response can prevent infectious microbes from causing serious problems, but other times infections can become severe. The combination of a serious infection and our own immune system’s response to it is what causes pneumonia.

People most at risk of infections and complications should take extra care to avoid people or situations where they will be exposed to the microbes that cause infections. As the bugs that cause pneumonia are contagious, people living in close quarters are at higher risk of having pneumonia. This includes people living in military barracks, student accommodation, and in care homes. People in care homes are also more likely to have other risk factors.

Pneumonia Risk Factors

Some people are more at risk than others, and being aware of your risk factors can help you make healthy choices to avoid serious illness.

Common risk factors include:

Having A Pre-Existing Condition

Existing health conditions that affect the lungs, such as chronic obstructive pulmonary disease (COPD), asthma, or heart failure can increase the chances of an individual developing pneumonia.

A Weakened Immune System

Some medications, particularly those given for cancer or for autoimmune diseases, disrupt the immune system and make it difficult to fight infections. Some conditions directly affect the immune system, such as AIDS.


Young children and the elderly population are more likely to develop pneumonia and related complications.


Smokers are much more likely to develop pneumonia and other lung disorders. Second-hand smoke is just as harmful and children who live in houses where people smoke are more likely to get pneumonia.


Dysphagia refers to difficulty in swallowing. People with dysphagia often have a reduced gag and cough reflex, meaning that food, fluids, and all kinds of microbes can enter the windpipe and stay in the lungs. Groups who may suffer from dysphagia include people with Parkinson’s disease or advanced dementia and individuals who have had a stroke.

Spinal Cord Injuries

Aside from potential swallowing difficulties, people with severe spinal cord injuries may be reliant on mechanical ventilation and have complex tracheostomy (a breathing tube through the front of the throat into the windpipe) care needs. They may also be unable to cough without mechanical assistance and hence find it harder to clear their lungs.

A Recent Illness

Having had a recent illness or being generally run-down and unwell can mean that it’s harder to fight off further illnesses.

Preventing Pneumonia

Pneumonia cannot always be prevented, but there are some steps we can take to avoid becoming ill, and to ensure that we’re able to recover as quickly and fully as possible when we do become ill.

Quit Smoking

Stopping smoking is one of the best things you can do for all aspects of your health, and that of the people around you. Smoking directly causes serious lung diseases and impairs the natural defences of the respiratory system.

Observe Good Hygiene Standards 

Handwashing, using and promptly throwing away tissues, and avoiding mingling with people who are ill can help to reduce our chances of developing pneumonia. If everyone follows basic hygiene standards, the risks of passing on coughs and colds can be greatly reduced.

Stay Healthy

We can’t always avoid catching a cough or chest infection, but if we generally follow a healthy lifestyle to try and maintain a baseline of good health, we’re less likely to become seriously unwell.

Manage Existing Conditions

If you have specific risk factors for pneumonia, managing them as well as possible is important. Maintaining good control of conditions like asthma or heart failure, and attending regular chronic disease management appointments can help prevent further complications.

Stay Up-To-Date With Vaccinations

Those at a higher risk of developing pneumonia are recommended to have seasonal vaccines. These include the flu vaccine and pneumococcal vaccine, which protects against a kind of bacteria that commonly causes pneumonia.

If you’re worried about being at risk of pneumonia and would like to discuss your health or concerns, a number of GP services are available, including online consultations and house calls.

Types of Pneumonia

There are several ways of describing pneumonia; we may talk about the areas of the lungs affected and the type of microbe that caused the infection. We may also talk about the way a person acquired pneumonia, which tells us a lot about the kind of microbe that may have caused it and the kind of path the illness may take.

Here are some of the common types of pneumonia:

Community-Acquired Pneumonia

This refers to pneumonia that started in the community and not in a hospital or institutional setting.

Hospital-Acquired Pneumonia

This refers to pneumonia which developed in a hospital, secondary to the reason for admission. It also has to be at least 48 hours after admission, as pneumonia which develops within 48 hours is most likely to come from a microbe caught in the community. 

People in hospitals are usually in close proximity to other people who are unwell and may have a compromised immune system due to existing illnesses. Hence, they may be more exposed to certain sorts of viruses and bacteria while in the hospital, including some which are harder to treat with antibiotics.

Ventilator-Acquired Pneumonia

Also referred to as ventilator-associated pneumonia, ventilator-acquired pneumonia is a type of hospital-acquired pneumonia which occurs when people are intubated and mechanically ventilated in a hospital’s intensive care unit. This means they have a tube in their throat attached to a machine which helps them to breathe or breathes for them. People on ventilators in intensive care are already unwell and so developing ventilator acquired pneumonia as a secondary complication can be highly dangerous.

Aspiration Pneumonia

This is a type of pneumonia developed as a result of food, fluid, or stomach contents entering the lungs. It usually occurs in people who have conditions resulting in the loss of their gag or cough reflex. This sometimes happens after a stroke, brain injury, or advanced dementia. Dislodged or misplaced nasogastric tubes are also a cause of aspiration pneumonia.

When food and fluids enter the lungs, they irritate and obstruct the delicate airways, introducing millions of microbes into the lung. Aspiration pneumonia is more common in the lower lobe of the right lung as the anatomy of the airways means that solids and liquids are more likely to be inhaled in that direction.

‘Walking’ or ‘Atypical’ Pneumonia 

Sometimes, people have a milder form of pneumonia and do not become severely ill; they may be able to continue normal activities but feel a little unwell. People may feel that the symptoms are too mild to see a doctor and have a proper diagnosis, and so ‘walking’ pneumonia may be more common than we realise.

Diagnosing Pneumonia

Typically, investigations for pneumonia begin when someone presents to their doctor or at a hospital with the symptoms of a chest infection – usually breathlessness, chest pain, coughing, and feeling generally unwell. The doctor will ask about your medical history, particularly risk factors and exposure, and the symptoms you are experiencing.

The doctor will need to listen to the sounds of your breathing so will use a stethoscope held against a few different places on your chest and back. The doctor may also use a pulse oximeter, which is a device that clips onto your fingertip, to measure the amount of oxygen in your blood.

A chest X-ray is one of the best tools used to diagnose and plan treatment for pneumonia, as it enables the doctor to visualize the amount of inflammation and fluids in the lungs, and exactly where they are. An x-ray can also show if there are any larger collections of fluid in or around the lungs. If your cough is ‘productive’ – if you are coughing up any phlegm – a sample should be taken to try and find out the specific type of microbe causing the infection. 

Signs and Symptoms of Pneumonia

Some of the signs of pneumonia are generalised, including aches, nausea and fatigue. Others could have more specific signs of infection, such as a fever, or, in some people, feeling confused.

The specific signs which indicate a chest infection or acute respiratory problem are:

  • A cough, especially if it brings up thick sputum.
  • Shortness of breath during exercise, or sometimes at rest too.
  • Chest pain, which may get worse when breathing or coughing.

A doctor or other healthcare professional can check for more signs of infection by measuring your oxygen levels, listening to the sounds of your breathing, and monitoring other vital signs such as blood pressure and heart rate.

Managing Pneumonia

Pneumonia management is different for everyone, depending on the underlying cause and your health condition. Some cases of pneumonia can be managed at home, whereas others will need hospital admission.

Managing Pneumonia At Home

Less severe cases of pneumonia can be managed at home. Maintaining an upright or slightly inclined position can help to keep the lungs clear. If you experience pain and fever, over-the-counter medications can help. A doctor may also prescribe antibiotic tablets if they think it is likely to be a bacterial infection. If you’re managing pneumonia at home, it’s important to know when to see a doctor or get more urgent help – if you become short of breath, drowsy, or develop severe pain.

Managing Pneumonia In Hospitals

In a hospital, healthcare professionals will closely monitor your temperature, breathing rate, oxygen levels, heart rate and blood pressure. This helps to guide treatment and identify problems early. People with severe infections may need to be given intravenous (drip) fluids and antibiotics.

Blood tests and sputum samples may be taken to make sure any antibiotics are targeting the right types of microbe. Doctors and nurses can also try to identify and manage any underlying cause of this pneumonia, for example, a reduced swallowing ability. Treatment in hospitals means that there are more options for treatment if pneumonia becomes more serious, such as specialist physiotherapists to help with breathing exercises to clear the lungs, non-invasive ventilators, and oxygen therapy.

Treatment for Pneumonia

Mild cases of pneumonia, particularly in people without any significant risk factors, may be manageable at home, but should be assessed by a doctor. Seeing a doctor means that they can prescribe antibiotics if they think it is likely to be bacterial pneumonia. Rest, fluids, antibiotics and simple over-the-counter treatments for pain and fever may be enough to treat mild cases of pneumonia.

For more severe cases of pneumonia, with chest pain, breathing difficulties and where the person becomes seriously unwell, a hospital admission will be necessary. Sometimes, people with mild pneumonia but who are at risk of becoming seriously ill and unable to clear the infection at home – people on medication to suppress the immune system, for example – may be admitted to hospital before they become seriously unwell.

In hospital, treatment for pneumonia will most likely take the form of strong intravenous (IV) antibiotics, IV fluids, and possible oxygen through a mask or a tube that sits in the nostrils. Vital signs will also be taken regularly to monitor your progress. This will include measuring your blood pressure, temperature, oxygen levels, heart rate and breathing rate.

Complications of Pneumonia

Most people, particularly those who are reasonably healthy to start with, recover from pneumonia with no complications. However, pneumonia can be a serious illness and is not always easy to treat. Severe pneumonia can trigger other serious conditions such as:

  • Sepsis: This is where the body’s inflammatory response to infection affects several organ systems. Kidney, heart and lung function may all be reduced. Around 20% of all deaths worldwide are caused by sepsis.
  • Abscesses in the lungs: A pocket of infected pus could develop in the lung. Larger abscesses may need to be drained.
  • Respiratory failure: This may occur if the function of the lungs is so reduced that the gas exchange is unable to meet the body’s demand. People with respiratory failure can become ill very quickly and need intensive care.

Staying Well And Getting The Right Care

The people most at risk of contracting or developing serious complications from pneumonia are usually those who already have other illnesses. Leading a healthy lifestyle, going for regular health screenings and ensuring that you are generally healthy is important. If you’re concerned about symptoms, risks, or how you can manage at home while you’re unwell, help is always available.

If you need support caring for a loved one with pneumonia, we can help.

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About the Writer
Elaine Francis, R.N.
Elaine Francis is a registered nurse with 17 years’ experience in healthcare. She turned to writing to follow her passion for realistic medical communication. She loves translating medical jargon into accessible language for the people who need to understand it most. When she’s not writing or working on a busy cardiology unit, she spends her time telling her children to hurry up.
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