What is it?
Pneumonia is an infection of the lungs, an invasion of lower respiratory tract by microrganisms that can cause a disease that ranges from mild to life-threatening. Worldwide, pneumonia kills more people than any other infectious disease, more than 4 million people a year, half of them under 5 years old.
Although anyone can get pneumonia, it is most common and potentially severe in those who are very young, over 65, immune compromised, or who have an another disease or condition that affects their lungs. This group of conditions includes people who have HIV/AIDS or have had an organ transplant and those who are on chemotherapy for cancer, are pregnant, in intensive care (ICU), on mechanical ventilation, have scarred or damaged lungs as occurs from smoking, or who have a lung disease such as cystic fibrosis.
Pneumonia can occur at any time, but the greatest numbers of cases are seen in the late autumn through to early spring. Infection of the lungs can occur in five different ways:
- Microorganisms can move downwards from the breathing airways into the lungs
- Airborne droplets from a sneeze or cough can be inhaled
- Surfaces contaminated with mucus or other respiratory secretions when touched by hands can spread through the mouth or eyes
- Microorganisms in a person's own mouth or stomach can enter the lungs
- An infection may spread from another site in the body, through the blood and into the lungs
It takes more than exposure to a potential disease-causing microorganism (pathogen) to get pneumonia. Microorganisms are always present in the environment, and we are exposed to infection daily. In most cases, the lungs can take care of these infections. The body has layers of defences that include mechanical barriers, protective microorganisms (normal flora), and the immune system. Pneumonia occurs when these defences are weakened or damaged and/or when the invading microorganisms are strong enough to overcome them.
A wide range of viruses, bacteria, and (less commonly) fungi or parasites can cause pneumonia, but the majority of cases are due to just a few of these. The most likely microorganism to cause pneumonia will depend upon the age and health of the person and on the time of the year. Those with poor immune systems and those who have been traveling abroard may develop pneumonia that is due to more unusual microorganisms.
Pneumonia may be grouped by the medical community into different categories. These distinctions are most useful in finding a cause of the pneumonia, how best to prevent its spread, and in guiding treatment.
- Community-acquired pneumonia—when a person becomes infected during normal daily activities
- Hospital-acquired pneumonia—when an infection occurs, for example, after surgery while connected to a ventilator or in an intensive care unit
- Healthcare-associated pneumonia—when a person is infected from a healthcare establishment such as a nursing home or dialysis clinic
Hospital-acquired and healthcare-associated microorganisms are more likely to be resistant to first-line antibiotics where as community-acquired pneumonia is more likely to be due to bacteria that are susceptible to commonly prescribed antibiotics or due to seasonal viruses for which antimicrobial agents are not the appropriate treatment.
Pneumonia symptoms vary, depending on the age and health status of the person affected and on the microorganism causing the infection. Very young infants may grunt and wheeze, breathe rapidly, and be irritable and/or lethargic. The elderly may experience confusion. Bacterial pneumonia may emerge following a viral infection and may just be seen as a lingering or worsening cold or bout of the flu. Common pneumonia symptoms include:
- Cough
- Fever and chills
- Tiredness
- Shortness of breath
- Headache
- Muscle aches
- Chest pain
- Nausea and vomiting
Complications
Complications that can occur with pneumonia include the build-up of fluid in the lungs, the scarring of lung tissue (which can lead to recurrent infections), respiratory failure, sepsis, and rarely lung abscesses (pockets of pus in lung tissue).
The goals with testing are to find out what is the microorganism causing the pneumonia, to limit it’s spread to other people, to determine the severity of the pneumonia, and to guide treatment. It is often not possible to workout the exact cause of acute pneumonia, and treatment is then based symptoms, medical history, the doctor's experience, likely microorganisms present in the community at the time, and on established guidelines for the care of lower respiratory infections. If treatment is not working then tests may be performed to help diagnose less common causes of pneumonia.
Non-laboratory Tests
The search for the cause of symptoms typically begins with a physical exam. As part of the exam, a doctor listens to a person's lungs for abnormal rumbling, crackling, and bubbling noises that may indicate a lung infection. This is often followed with imaging studies. These may include:
- Chest X-ray - used to detect and help evaluate the severity of lung infection
- CT (Computed Tomography) scan — sometimes use to detect and evaluate lung infection and to look for other causes of a person's symptoms
Laboratory Tests
Depending on the affected person's medical history and the signs and symptoms that are present at the time of the physical exam, a number of laboratory tests may be performed to help make a diagnosis.
General laboratory tests may include:
- FBC (Full Blood Count) — requested to evaluate the type and number of white blood cells
- Urea & Electrolytes “U&E”s — blood tests for sodium, potassium, and other chemicals to help determine the severity of the illness
- Arterial Blood gases — to also help determine the severity of the illness by assessing how much oxygen, carbon dioxide and hydrogen ion (pH) is in the blood.
Tests for suspected bacterial pneumonia
- Sputum culture and Gram stain — primary tests requested to detect and identify the cause of bacterial pneumonia
- AFB smear and culture — requested when tuberculosis or a non-tuberculous mycobacteria infection is suspected
- Blood culture — used to detect septicaemia when it is suspected that infection has spread from the lungs to the blood or from the blood to the lungs
Tests for suspected viral pneumonia:
- Polymerase chain reaction (PCR) — to detect a broad range of viral pathogens in respiratory secretions or a nose or throat swab.
Other types of tests that may be performed depending on patient history and clinical presentation:
- Pleural fluid analysis — if fluid has accumulated in the space between the lungs and chest wall, the fluid may be tested to help determine the cause of infection
- Fungal culture — sometimes ordered when a fungal infection is suspected
- Mycoplasma testing — blood test or special culture to help diagnose a mycoplasma infection
- Legionella testing — urine test for the specific antigen; culture or molecular test on respiratory secretions; or blood sample for antibodies to diagnose a suspected Legionella infection
Individuals can protect themselves from causes of pneumonia by following good hygiene practices. Such practices as frequent hand washing, coughing or sneezing into a tissue, elbow or sleeve, and cleaning surfaces that are regularly touched by hands prevent contact with these pathogens.
Several vaccines are available to help protect against or decrease the risk of certain types of pneumonia, including pneumococcal, Haemophilus influenzae type b, seasonal influenza, and several others. People should talk to their doctors about these options.
Bacterial and mycoplasma pneumonias are typically treated with antibiotics. Fungal infections are treated with antifungal medications. Some infections may require treatment for an extended period of time.
Those with viral pneumonia are sometimes treated with antiviral medications but often are just given supportive care.
People with severe cases of pneumonia may require admission to hospital, treatment with oxygen or other breathing assistance, and intravenous antimicrobial drugs.