Bacterial pneumonia is a serious infection of the lungs caused by bacteria. The three most common causes of bacterial pneumonia are Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus.
Streptococcus pneumoniae
Streptococcus pneumoniae, also called pneumococcus, is the most common cause of bacterial pneumonia in adults. S. pneumoniae is a gram-positive, lancet-shaped bacterium that often lives in the throat of healthy people. It can spread from person to person via respiratory droplets from coughing or sneezing. When the bacteria make their way into the lungs, they can cause an infection.
Pneumonia caused by S. pneumoniae starts out with symptoms like a cold or the flu. Symptoms include:
- Fever and chills
- Cough, which may produce mucus
- Rapid, shallow breathing
- Chest pain when breathing deeply or coughing
- Fatigue
As the infection worsens, pneumonia symptoms get more severe. People may feel very short of breath and have a high fever. The cough may produce thick yellow, green, or blood-tinged mucus. In very serious cases, the lips or fingernails may look blue or purple from lack of oxygen.
Risk factors for getting pneumococcal pneumonia include:
- Being over age 65
- Having certain chronic illnesses like heart or lung disease, cancer, or diabetes
- Smoking cigarettes
- Having a weakened immune system
S. pneumoniae spreads easily in settings like daycares, nursing homes, military barracks, and jails where people live in close quarters. Pneumococcal pneumonia often happens in winter and early spring when respiratory illnesses are most common.
Doctors diagnose pneumococcal pneumonia based on symptoms and by listening to the lungs with a stethoscope. A chest x-ray can confirm the diagnosis and show the extent of the infection. Pneumonia caused by S. pneumoniae can usually be treated with antibiotics. Very severe cases may require hospitalization.
There are vaccines available to prevent pneumococcal pneumonia in infants, young children, adults over 65, and people with certain medical conditions. Good hand hygiene helps prevent the spread of the bacteria. Overall S. pneumoniae is responsible for about 1 million pneumonia infections each year.
Key Points on Streptococcus pneumoniae
- Gram-positive bacterium that commonly lives in the throat
- Spread by respiratory droplets from coughing and sneezing
- Causes fever, cough, chest pain and more severe symptoms
- Most common cause of pneumonia in adults
- Treated with antibiotics and prevented with vaccination
Haemophilus influenzae
Another very common cause of bacterial pneumonia is Haemophilus influenzae (H. influenzae). This bacterium was originally called Pfeiffer’s bacillus. There are six subtypes of H. influenzae labeled a through f. The b subtype, also known as Hib, most often causes pneumonia.
Like S. pneumoniae, H. influenzae bacteria commonly live in the throats and noses of healthy people. The bacteria can be spread by coughing, sneezing, or touching contaminated surfaces. When H. influenzae migrates into the lungs, it can lead to pneumonia, particularly in adults with chronic health conditions.
Pneumonia caused by H. influenzae starts out with typical pneumonia symptoms like:
- Fever and chills
- Cough producing green or yellow mucus
- Shortness of breath, especially with activity
- Rapid heartbeat
- Muscle aches
As the H. influenzae pneumonia gets worse, people may feel very confused and fatigued. Coughing up blood-stained mucus may also occur. H. influenzae pneumonia can progress very quickly, sometimes leading to respiratory failure.
Those at increased risk for H. influenzae pneumonia include:
- Infants and young children
- Adults over 65 years old
- People with heart or lung conditions like COPD
- Individuals with weakened immune systems
- Smokers
H. influenzae spreads through daycares, hospitals, and other environments where people have close contact. Pneumonia caused by this bacteria most often occurs during fall and winter.
Doctors use a sputum culture or blood test to diagnose H. influenzae pneumonia. Treatment involves antibiotics, with very ill patients needing care in the intensive care unit. There are vaccines available to prevent Hib pneumonia in infants and children.
Key Points on Haemophilus influenzae
- Gram-negative coccobacillus bacterium
- Spread by respiratory droplets from coughing and sneezing
- Causes fever, cough, shortness of breath, and confusion
- More common in infants, elderly, those with chronic illness
- Treated with antibiotics and prevented with vaccination
Staphylococcus aureus
The third most frequent cause of bacterial pneumonia is Staphylococcus aureus (staph). This bacterium lives on the skin and in the noses of about 30% of healthy people. Staph can cause illness when it gets into cuts, wounds, or the lungs.
Pneumonia caused by methicillin-resistant Staphylococcus aureus (MRSA) has been increasing over the past few decades. MRSA is resistant to some commonly used antibiotics, making these pneumonias more difficult to treat.
Symptoms of staph pneumonia usually come on quickly and include:
- High fever
- Shaking chills
- Chest pain
- A cough that brings up thick, bloody mucus
- Shortness of breath
- Clammy, sweaty skin
Staph pneumonia progresses rapidly. It often leads to abscesses or fluid accumulation in the lungs. Sometimes holes or cavities form in the lungs.
People at increased risk for staph pneumonia include:
- Those hospitalized for other conditions
- People with viral respiratory infections
- Individuals with weakened immune systems
- Intravenous drug users
- Elderly adults
- People with chronic lung conditions
Staph spreads through direct contact with someone who has an active infection. Coughing and sneezing also transmit the bacteria. Staph pneumonia can occur year-round.
Doctors diagnose staph pneumonia using a sputum culture. Treatment involves strong antibiotics. Intravenous antibiotics are needed for severe cases. Often, treatment occurs in the ICU.
Preventing the spread of staph involves good handwashing. Those at risk may receive a pneumonia vaccine. Even with treatment, staph pneumonia has a high mortality rate.
Key Points on Staphylococcus aureus
- Gram-positive bacterium that lives on the skin and in nasal passages
- Increasing cases of pneumonia from antibiotic-resistant MRSA
- Causes fever, chest pain, bloody mucus, and lung abscesses
- More common in those with weakened immune systems
- Treated aggressively with antibiotics in hospital setting
Comparison of the Three Main Bacterial Causes of Pneumonia
| Bacteria | Streptococcus pneumoniae | Haemophilus influenzae | Staphylococcus aureus |
|---|---|---|---|
| Type | Gram-positive | Gram-negative | Gram-positive |
| Habitat | Respiratory tract | Respiratory tract | Skin, nose |
| Transmission | Respiratory droplets | Respiratory droplets | Contact, droplets |
| Symptoms | Fever, cough, chest pain | Fever, cough, confusion | Fever, chills, bloody mucus |
| Risk Factors | Elderly, smokers, chronic illness | Infants, elderly, chronic illness, smokers | Weak immune system, hospitalization |
| Prevention | Vaccination | Vaccination | Handwashing, vaccination in some |
Conclusion
Pneumonia caused by bacteria leads to over a million hospitalizations each year in the United States. The three most frequent bacterial causes of pneumonia are Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus.
S. pneumoniae is responsible for most pneumonia cases in adults, especially those who are elderly, smokers, or have chronic health conditions. Vaccination helps prevent infection. H. influenzae pneumonia mainly affects infants, young children, and those over 65 years old. Staph pneumonia occurs most often in people with weakened immune systems. Antibiotic-resistant MRSA is an increasing cause.
All three types of bacterial pneumonia have some similarities. They are spread by respiratory secretions and cause fever, cough, and chest pain. However, they also have some differences in their risk factors, typical symptoms, and treatment approaches.
While bacterial pneumonia can be serious and sometimes fatal, antibiotics and improved prevention methods have led to better outcomes. Seeking prompt medical treatment at the first signs of pneumonia is key to recovery. With appropriate care, most people can overcome these common bacterial lung infections.