Like many illnesses, there isn't just one primary cause of pneumonia; certain strains can be brought on by many different types of germs that you inhale, including viruses, bacteria and fungi.
• Bacterial pneumonia affects people of all ages, and can either develop on its own or after a severe case of cold or flu.1
• Viral pneumonia is brought on by respiratory viruses, and is prevalent in young children and seniors. This is usually not serious, and heals in a short span of time. However, viral pneumonia caused by the flu virus can be severe or fatal, and is especially dangerous to pregnant women or individuals with heart or lung problems. Bacteria can also lead to complications with viral pneumonia.
• Fungal pneumonia is caused by opportunistic fungi and may develop upon the inhalation of damaging spores, such as stirred up into the air from the soil, or from birds' droppings.2 Although it is relatively uncommon in most of the U.S, fungal pneumonia is most prevalent in locations such as Mexico, South America and Africa.3
Examples of infections that can lead to fungal pneumonia include histoplasmosis, cryptococcosis coccidioidomycosis, aspergillosis and blastomycosis.4
Another potential cause of pneumonia is mycoplasma. Mycoplasma are the smallest free-living disease agents known today. They are neither bacteria nor virus, yet they possess traits of both. Mycoplasma usually leads to a mild form of pneumonia, although it can become severe in some cases. It affects all age groups, but is most common in older children and young adults.
Most of the time, your body can effectively filter out these harmful organisms — your immune system, your ability to cough and the cilia (small hair-like structures) in your nose all work together to keep these germs out of your lungs and body.
However, there are instances when the germs manage to infiltrate your body and enter your lungs, leading to infections. Factors that may influence this include:
- Having a weak immune system
- When the fungi, bacteria strain or virus is very strong
- Being unable to cough, such as when you're sedated or you've had a stroke — this causes germs to stay in your airway
When these damaging organisms reach your lungs, your immune system immediately goes into action, and sends many types of cells to attack the invading organism. These cells cause your lungs' alveoli or air sacs to become red and inflamed, filling up with fluid and pus. This is what leads to the common symptoms of pneumonia.
So, how do you catch these pneumonia-causing organisms? They can be acquired through different settings, such as:
- Your community or environment — Also known as community-acquired pneumonia, this refers to pneumonia cases that come from sources other than hospitals or health care facilities.
- Hospital-acquired pneumonia — This refers to pneumonia that develops during a hospital stay, and may be more serious, as the bacteria may be more resistant to antibiotics. Patients who use ventilators and other breathing machines are at a high risk of this type.
- Health care acquired pneumonia — People who live in long-term care facilities such as nursing homes, or who are treated in outpatient clinics and kidney dialysis centers, are at high risk of health care acquired pneumonia.
Another possible cause of pneumonia is aspiration, which occurs when you accidentally inhale food, saliva or vomit into your lungs. Aspiration pneumonia is most common in people who have problems with their gag reflex, such as those with brain injury or who excessively use drugs or alcohol.5 Knowing the cause of pneumonia is crucial in determining the course of treatment for this illness.