August 22, 2020

Pneumonia: key facts, causes, risk factors, features, treatment, prevention and prognosis

Pneumonia is one of the most common reasons people go to see their doctor. Strictly speaking it describes any inflammatory condition affecting the alveoli of the lungs, although in the vast majority of patients this is due to a bacterial infection.

What is pneumonia?

Pneumonia, in the strict sense of the word, is any inflammatory condition affecting the alveoli of the lungs, however in the vast majority of cases it is due to an acute infection, usually by bacteria. It is right, therefore, to say pneumonia is a form of acute respiratory infection that affects the lungs.

The lungs are made up of small sacs called alveoli, which fill with air when a healthy person breathes (see fig 1 below). When an individual has pneumonia, the alveoli are filled with pus and fluid, which makes breathing painful and limits oxygen intake (see fig 2 below).

Human lungs showing the different parts
Fig 1: A diagram of the anatomy of the normal human lungs, including a close-up of an alveolus.

The alveolus in Pneumonia
Fig 2: Pneumonia fills the lung's alveoli with fluid, hindering oxygenation. The alveolus on the left is normal, whereas the one on the right is full of fluid from pneumonia.
Pneumonia is the single largest infectious cause of death in children worldwide. Pneumonia killed 808 694 children under the age of 5 in 2017, accounting for 15% of all deaths of children under five years old. Pneumonia affects children and families everywhere, but is most prevalent in South Asia and sub-Saharan Africa. Children can be protected from pneumonia, it can be prevented with simple interventions, and treated with low-cost, low-tech medication and care.

Key facts about pneumonia

These are key facts to know about Pneumonia:
  • Pneumonia accounts for 15% of all deaths of children under 5 years old, killing 808 694 children in 2017.
  • Pneumonia can be caused by viruses, bacteria, or fungi.
  • Pneumonia can be prevented by immunization, adequate nutrition, and by addressing environmental factors.
  • Pneumonia caused by bacteria can be treated with antibiotics, but only one third of children with pneumonia receive the antibiotics they need.

Causes of pneumonia

Pneumonia is caused by a number of infectious agents, including viruses, bacteria and fungi. However, as mentioned earlier, bacterial pneumonia is by far the most common type of pneumonia seen in clinical practice. The most common infections are:
  • Streptococcus pneumoniae – the most common cause of bacterial pneumonia;
  • Haemophilus influenzae type b (Hib) – the second most common cause of bacterial pneumonia;
  • Respiratory syncytial virus is the most common viral cause of pneumonia;
  • In infants infected with HIV, Pneumocystis jiroveci (a fungus) is one of the most common causes of pneumonia, responsible for at least one quarter of all pneumonia deaths in HIV-infected infants.
The table below shows some of the organisms which can cause pneumonia
Streptococcus pneumoniae
Accounts for 80% of cases
Particularly associated with high fever, rapid onset and herpes labialis
A vaccine to pneumococcus is available
Haemophilus influenzaeParticularly common in patients with COPD
Staphylococcus aureusOften occurs in patient following influenza infection
Mycoplasma pneumoniaeOne of the atypical pneumonias, which often present a dry cough and atypical chest signs/x-ray findings
Autoimmune haemolytic anaemia and erythema multiforme may be seen
Legionella pneumophiliaAnother one of the atypical pneumonias
Hyponatraemia and lymphopenia common
Klebsiella pneumoniaeClassically seen in alcoholics
Pneumocystis jiroveciTypically seen in patients with HIV
Presents with a dry cough, exercise-induced desaturations and the absence of chest signs

Idiopathic interstitial pneumonia

Idiopathic interstitial pneumonia is a group of non-infective causes of pneumonia. Examples include cryptogenic organizing pneumonia which describes a form of bronchiolitis which may develop as a complication of rheumatoid arthritis or treatment with the drug, Amiodarone.

Community vs. hospital-acquired pneumonia

The majority of patients develop pneumonia within the community, i.e. outside of hospital and these patients are said to have community-acquired pneumonia (CAP). Patients who develop pneumonia within hospitals are said to have hospital-acquired pneumonia. The distinction is important as the causative organisms vary and hence first-line antibiotic guidelines are also different.

Transmission of pneumonia

Pneumonia can be spread in a number of ways. The viruses and bacteria that are commonly found in the nose or throat, can infect the lungs if they are inhaled. They may also spread via air-borne droplets from a cough or sneeze. In addition, pneumonia may spread through blood, especially during and shortly after birth in infants.

More research needs to be done on the different pathogens causing pneumonia and the ways they are transmitted, as this is of critical importance for treatment and prevention.

Risk factors for pneumonia

While most healthy children and adults can fight the infection with their natural defences, people whose immune systems are compromised are at higher risk of developing pneumonia. A person's immune system may be weakened by malnutrition or undernourishment, especially in infants who are not exclusively breastfed. See the separate article Infant and Young Child Feeding and also see Breastfeeding Dos' and Donts' You Need to Know.

Pre-existing illnesses, such as symptomatic HIV infections, diabetes, cancer, or even measles in children, are a few of the conditions that increase a person's risk of contracting pneumonia.

The following environmental factors also increase susceptibility to pneumonia:
  • indoor air pollution caused by cooking and heating with biomass fuels (such as wood or dung)
  • living in crowded homes
  • parental smoking, in the case of children.

Presenting features of pneumonia

The presenting features of viral and bacterial pneumonia are similar. However, the symptoms of viral pneumonia may be more numerous than the symptoms of bacterial pneumonia.

The symptoms patients often complain of are:
  • cough
  • sputum
  • shortness of breath (dyspnoea)
  • chest pain: may be pleuritic (i.e chest pain worsened on taking deep breaths)
  • fever
The signs trained health professionals look out for are:
  • signs of systemic inflammatory response: fever, abnormal fast heart beats (tachycardia)
  • reduced oxygen saturations
  • ausculatation: reduced breath sounds, bronchial breathing (a harsh type of sound heard from the lungs with the stethoscope)
In children under 5 years of age, who have cough and/or difficult breathing, with or without fever, pneumonia is diagnosed by the presence of either fast breathing (tachypnoea) or lower chest wall indrawing where their chest moves in or retracts during inhalation (in a healthy person, the chest expands during inhalation). Wheezing is more common in viral infections.

Very severely ill infants may be unable to feed or drink and may also experience unconsciousness, low temperatures (hypothermia) and convulsions.

Investigations for pneumonia

Important investigations for anyone suspected of having pneumonia are:

1). Chest x-ray
  • the classical x-ray finding in pneumonia is consolidation
x-ray of lobar pneumonia
Chest radiograph of a 67 year old man, showing lobar pneumonia, affecting the right middle lobe. Consolidation is seen in the right middle lobe. Credit: Mikael Häggström, M.D. Written informed consent was obtained from the patient, including for online publication. Public domain.
2). Bloods
  • full blood count: would usually show a neutrophilia in bacterial infections
  • urea and electrolytes: check for dehydration (remember the 'U' for urea in CURB-65, see below) and also other changes seen with some atypical pneumonias
  • CRP: raised in response to infection
3). Arterial blood gases
  • indicated if the oxygen saturations are low or the patient has pre-existing respiratory disease, for example COPD

Management and treatment of pneumonia

Patients with pneumonia require the following:
  • antibiotics: to treat the underlying infection
  • supportive care: for example oxygen therapy if the patient has low levels of oxygen in their blood (hypoxaemic), intravenous fluids if the patient is hypotensive or shows signs of dehydration
Pneumonia should be treated with antibiotics. The antibiotic of choice is amoxicillin dispersible tablets. Most cases of pneumonia require oral antibiotics, which are often prescribed at a health centre. These cases can also be diagnosed and treated with inexpensive oral antibiotics at the community level by trained community health workers.

However, the management of patients with community-acquired pneumonia is usually determined according to a risk stratification process using a scoring system called CURB-65. Hospitalization is recommended for severe cases of pneumonia.

The CURB-65 score is as follows:

CConfusion (abbreviated mental test score < or = 8/10)
UUrea >7 mmol/L
RRespiration rate > or = 30/min
BBlood pressure: systolic < or = 90 mmHg and/or diastolic < or = 60 mmHg
65Aged > or = 65 years
Score 1 point for each positive marker. Possible total score of 5 points.

Patients with a CURB-65 score of 0 should be managed in the community.

Patients with a CURB-65 score of 1 should have their oxygen saturations (Sa02) assessed which should be >92% to be safely managed in the community and a CXR performed. If the CXR shows bilateral/multilobar shadowing hospital admission is advised.

Patients with a CURB-65 score of 2 or more should be managed in hospital as this represents a severe community acquired pneumonia.

The CURB-65 score also correlates with an increased risk of mortality (i.e. death) at 30 days with patients with a CURB-65 score of 4 approaching a 30% mortality rate at 30 days.

Prevention of pneumonia

Preventing pneumonia is important for everyone, however it is an essential component of a strategy to reduce child mortality. Immunization against Hib, pneumococcus, measles and whooping cough (pertussis) is the most effective way to prevent pneumonia.

Adequate nutrition is key to improving children's natural defences, starting with exclusive breastfeeding for the first 6 months of life. In addition to being effective in preventing pneumonia, it also helps to reduce the length of the illness if a child does become ill.

Addressing environmental factors such as indoor air pollution (by providing affordable clean indoor stoves, for example) and encouraging good hygiene in crowded homes also reduces the number of individuals who fall ill with pneumonia.

In people infected with HIV, the antibiotic cotrimoxazole is given daily to decrease the risk of contracting pneumonia.

Prognosis of pneumonia

With treatment, most types of bacterial pneumonia will stabilize in 3–6 days. It often takes a few weeks before most symptoms resolve. X-ray findings typically clear within four weeks and mortality is low (less than 1%). In the elderly or people with other lung problems, recovery may take more than 12 weeks. In persons requiring hospitalization, mortality may be as high as 10%, and in those requiring intensive care it may reach 30–50%.

Pneumonia is the most common hospital-acquired infection that causes death. Before the advent of antibiotics, mortality was typically 30% in those that were hospitalized. However, for those whose lung condition deteriorates within 72 hours of hospital admission, the problem is usually due to sepsis. If pneumonia deteriorates after 72 hours, it could be due to hospital-acquired (nosocomial) infection or exacerbation of other underlying co-morbidities.

About 10% of those discharged from hospital are readmitted due to underlying co-morbidities such as heart, lung, or neurology disorders, or due to new onset of pneumonia.

Complications may occur in particular in the elderly and those with underlying health problems. This may include, among others: empyema, lung abscess, bronchiolitis obliterans, acute respiratory distress syndrome, sepsis, and worsening of underlying health problems

WHO and UNICEF response to pneumonia

The WHO and UNICEF integrated Global action plan for pneumonia and diarrhoea (GAPPD) aims to accelerate pneumonia control with a combination of interventions to protect, prevent, and treat pneumonia in children with actions to:
  • protect children from pneumonia including promoting exclusive breastfeeding and adequate complementary feeding. See the separate article Infant and Young Child Feeding and also see Breastfeeding Dos' and Donts' You Need to Know;
  • prevent pneumonia with vaccinations, hand washing with soap, reducing household air pollution, HIV prevention and cotrimoxazole prophylaxis for HIV-infected and exposed children. See the separate article How to Wash Your Hands the Right Way to Stay Healthy;
  • treat pneumonia focusing on making sure that every sick child has access to the right kind of care -- either from a community-based health worker, or in a health facility if the disease is severe -- and can get the antibiotics and oxygen they need to get well;
A number of countries have developed district, state and national plans to intensify actions for the control of pneumonia and diarrhoea. Many more have integrated diarrhoea and pneumonia specific action into their national child health and child survival strategies. For many countries the post Millenium Development Goal agenda has explicitly included ending preventable diarrhoea and pneumonia deaths as a priority action.

1). World Health Organization: Pneumonia - WHO Fact Sheets. Available online:
2). NICE (2014): Pneumonia in adults: diagnosis and management. Available online:
3). Behera, D. (2010). Textbook of pulmonary medicine (2nd ed.). New Delhi: Jaypee Brothers Medical Pub. pp. 296–97. ISBN 978-81-8448-749-7.
4). Nair GB, Niederman MS (November 2011). "Community-acquired pneumonia: an unfinished battle". The Medical Clinics of North America. 95 (6): 1143–61. doi:10.1016/j.mcna.2011.08.007. PMC 7127066. PMID 22032432.
5). Elena, Prina; Otavio, T Ranzani; Anthoni, Torres (12 August 2015). "Community-acquired pneumonia". The Lancet. 386 (9998): 1097–1108. doi:10.1016/S0140-6736(15)60733-4. PMC 7173092. PMID 26277247.
6). Eddy, Orin (December 2005). "Community-Acquired Pneumonia: From Common Pathogens To Emerging Resistance". Emergency Medicine Practice. 7 (12).

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