Lung Infection (Pneumonia): Symptoms, Signs and Diagnosis

Pneumonia causes more disease and death than any other infection in the US and the world, including from HIV, heart attacks, cancer, and malaria. There are more than three million cases of pneumonia each year in the United States.

Key takeaways:
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    There are more than three million cases of pneumonia each year in the United States.
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    Pneumonia is a disease where the alveoli (air sacs in the lungs) become inflamed.
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    There are different bacteria, viruses, and fungi that can cause pneumonia.
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    The most rapidly used test for diagnosis is the chest CT scan. The diagnosis is a result of taking in the entire clinical picture.

Pneumonia is a disease where the alveoli (air sacs in the lungs) become inflamed. There are different bacteria, viruses, and fungi that can cause pneumonia.

Pneumonia develops in two ways: extrinsic and intrinsic.

Extrinsic means exposure to the causative agent (usually a bacteria or virus), exposure to respiratory irritants, or direct injury to the lungs.

Intrinsic factors are related to the person (host), such as loss of protective airway reflexes or damage to the lungs themselves.

What is the respiratory system?

The respiratory system is the system made up of the organs and structures involved in ventilation, which is the process of bringing fresh air (oxygen) into the body and exhaling the stale air (carbon dioxide). Respiratory failure occurs when there is either too little oxygen (hypoxia) or too much carbon dioxide (hypercapnia).

Ventilation is important because it makes gas exchange possible, which is the process of swapping fresh oxygen from the lungs with stale carbon dioxide from the blood. The specific location where the gas exchange occurs is in tiny air sacs in the lungs called alveoli.

Gasses tend to move from an area of high concentration to a low concentration. This is the principle involved in the passive transportation mechanism known as diffusion. Gas exchange in our lungs occurs when the fresh air in the alveoli, rich in oxygen and low in carbon dioxide, comes close to the blood in the capillaries which is the opposite – it is low in oxygen and high in carbon dioxide.

For diffusion to occur, the two solutions that are exchanging gasses must be close together. The further they are apart, the lower the rate of diffusion, or gas exchange. That is why the alveoli, and the capillaries are practically stuck together.

To support absorption of oxygen and release of carbon dioxide, about five to eight liters (one-point-three to two gallons) of air per minute must be brought in and out of the lungs. It’s interesting to note that athletes can breathe in and out more than 100 liters (26 gallons) of air per minute during exercise.

In addition to distance, the other factor that determines the rate of diffusion is surface area. The greater the surface area, the greater the rate of diffusion. With hundreds of millions of alveoli, a human adult has lungs with potentially around 70 square meters or 750 square feet of surface area, allowing massive contact between the air in the lungs and the blood in the capillaries.

What is a respiratory disease?

A disease is a condition of the human body that impairs normal function.

Examples of diseases that can affect the respiratory system include emphysema, asthma, influenza, tuberculosis, and pneumonia. Diseases result from a variety of causes, ranging from genetic conditions to environmental pollutants to pathogens such as viruses and bacteria.

What is the difference between a bacterium and a virus?

Bacteria are small, single-celled, microscopic organisms. They are found almost everywhere and are vital to our planet’s ecosystems. Most bacteria are harmless, and some are even helpful. Only a few species cause disease.

Normally, our bodies can have up to 10 times more bacterial cells than human cells.

Bacteria are comparatively much larger than viruses. The size difference can be 100 to 1,000 greater, like a person standing next to a skyscraper. Bacteria lack a distinct nucleus and are called prokaryotes. Cells that have a nucleus are eukaryotes. Bacteria reproduce asexually through a process called binary fission.

Viruses are submicroscopic as well, and consist of a segment of DNA or RNA surrounded by a coat of protein, and which need a host cell in order to replicate.

What are the common causes of pneumonia?

A common cause of pneumonia is a bacterium known as Streptococcus pneumoniae (pneumococcus).

Other common causes are influenza, respiratory syncytial virus (RSV), and SARS-CoV-2 or COVID-19.

All pneumonias can spread when an infected person breathes out and there are tiny droplets of sputum and small particles that contain the pathogen. These droplets and particles can be breathed in by others or land on surfaces (as fomites) and people can become infected by touching the surfaces and then their mouths or eyes.

During the pandemic, precautions include distancing six feet apart, using gloves, hand sanitizer, and cleaning surfaces, which help reduce the transmission of germs.

How is pneumonia diagnosed?

The diagnosis of patients with suspected pneumonia depends on how sick the person is and if the accuracy of the diagnosis will alter empiric treatment. Diagnosis of the specific pathogen can be useful in determining the potential severity of the disease and how best to oversee the patient’s care.

With the more dangerous variants of COVID-19, diagnosis is paramount to try to avoid the need for inpatient care or the intensive care unit (ICU).

When everyone thinks about the possibility of pneumonia, we all think of a chest Xray.

While a chest Xray definitely remains the gold standard in diagnosis, it has drawbacks, including:

  • Chest X-Rays do not identify the cause of pneumonia, including the type of pathogen.
  • Chest X-Rays can be limited in accuracy for detecting pneumonia.
  • The accuracy of chest X-Rays detecting pneumonia decreases depending on the setting os the infection. That is, where the infection is in the lungs, for example.

here are many other tests that a doctor will use to determine if a patient has pneumonia, including routine laboratory tests, blood studies, sputum evaluation, transtracheal aspiration, chest ultrasound, bronchoalveolar lavage (taking washings of the lungs using a bronchoscope), or thoracentesis (obtaining fluid from the pleural space for laboratory analysis using a long needle).

Perhaps, the most rapidly used test now is the chest CT scan, although its usefulness is still evolving. The chest CT scan offers a look into the patterns of disease.

Abnormalities may include diverse types of lung opacities on CT scan. These patterns can offer vital diagnostic information.

In the diagnosis of COVID pneumonia and other types of influenza, often patients have a test called the ground glass opacity on a CT scan. This can be especially useful in determining how to treat a patient, monitor the extent of involvement, and also, aid in management as the patient improves.

Pneumonia can affect anyone at any time. The diagnosis is a result of taking in the entire clinical picture.

Most consistently the presenting symptom when someone has pneumonia is a cough producing sputum. But, like most diseases, pneumonia can fool both patients and healthcare providers with many different presentations.


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