Bacterial pneumonia

See pneumonia for a general overview of pneumonia and its other causes.

Bacterial pneumonia
Specialty	Pulmonology

Bacterial pneumonia is a type of pneumonia caused by bacterial infection.

Sign and symptoms

• Fever
• Rigors
• Cough
• Dyspnea
• Chest pain
• Pneumococcal pneumonia can cause Hemoptysis

Types

Gram positive

Streptococcus pneumoniae (J13) is the most common bacterial cause of pneumonia in all age groups except newborn infants. Streptococcus pneumoniae is a Gram-positive bacteria which often lives in the throat of people who do not have pneumonia.

Another important Gram-positive cause of pneumonia is Staphylococcus aureus (J15.2).

Gram negative

Gram-negative bacteria are seen less frequently: Haemophilus influenzae (J14), Klebsiella pneumoniae (J15.0), Escherichia coli (J15.5), Pseudomonas aeruginosa (J15.1) , Neisseria meningitidis, and Moraxella catarrhalis are the most common.

These bacteria often live in the gut and enter the lungs when contents of the gut (such as vomit or faeces) are inhaled.

Atypical

"atypical" bacteria are Coxiella burnetii, Chlamydophila pneumoniae (J16.0), Mycoplasma pneumoniae (J15.7), and Legionella pneumophila.

Many people falsely believe they are called "atypical" because they are uncommon and/or do not respond to common antibiotics and/or cause atypical symptoms. In reality, they are "atypical" because they do not gram stain like gram negative and gram positives organisms do.

Pneumonia caused by Yersinia pestis is usually called pneumonic plague.

Others

Mycobacterium tuberculosis may cause bacterial pneumonia.

Pathophysiology

Bacteria typically enter the lung with inhalation, though they can reach the lung through the bloodstream if other parts of the body are infected. Often, bacteria live in parts of the upper respiratory tract and are continually being inhaled into the alveoli. Once inside the alveoli, bacteria travel into the spaces between the cells and also between adjacent alveoli through connecting pores. This invasion triggers the immune system to respond by sending white blood cells responsible for attacking microorganisms (neutrophils) to the lungs. The neutrophils engulf and kill the offending organisms but also release cytokines which result in a general activation of the immune system. This results in the fever, chills, and fatigue common in bacterial and fungal pneumonia. The neutrophils, bacteria, and fluid leaked from surrounding blood vessels fill the alveoli and result in impaired oxygen transportation.

Bacteria often travel from the lung into the blood stream and can result in serious illness such as septic shock, in which there is low blood pressure leading to damage in multiple parts of the body including the brain, kidney, and heart. They can also travel to the area between the lungs and the chest wall, called the pleural cavity.

Treatment

Antibiotics are the treatment of choice for bacterial pneumonia and ventilation (oxygen supplement) as supportive therapy. The antibiotic choice depends on the nature of the pneumonia, the microorganisms most commonly causing pneumonia in the geographical region, and the immune status and underlying health of the individual. In the United Kingdom, amoxicillin is used as first-line therapy in the vast majority of patients who acquire pneumonia in the community, sometimes with added clarithromycin. In North America, where the "atypical" forms of community-acquired pneumonia are becoming more common, clarithromycin, azithromycin, or fluoroquinolones as single therapy, have displaced the amoxicillin as first-line therapy. Local patterns of antibiotic-resistance should always be considered when initiating pharmacotherapy. In hospitalized individuals or those with immune deficiencies, local guidelines determine the selection of antibiotics. These antibiotics are typically given through an intravenous line.

Gram-positive organisms

Streptococcus pneumoniae - amoxicillin (or erythromycin in patients allergic to penicillin); cefuroxime and erythromycin in severe cases. Staphylococcus aureus - flucloxacillin (to counteract the organism's β-lactamase)

Gram-negative organisms

• Haemophilus influenzae - doxycycline
• Klebsiella pneumoniae
• Escherichia coli
• Pseudomonas aeruginosa ciprofloxacin
• Moraxella catarrhalis

Atypical organisms

• Chlamydophila pneumoniae - doxycycline
• Chlamydophila psittaci - erythromycin
• Mycoplasma pneumoniae - erythromycin
• Coxiella burnetti - erythromycin
• Legionella pneumophila - erythromycin, with rifampicin sometimes added.

People who have difficulty breathing due to pneumonia may require extra oxygen. An extremely sick individual may require artificial ventilation and intensive care as life-saving measures while his or her immune system fights off the infectious cause with the help of antibiotics and other drugs.

Prevention

Prevention of bacterial pneumonia is by vaccination against Haemophilus influenzae type B, meningococcus, streptococcus pneumoniae (pneumococcal polysaccharide vaccine for adults and pneumococcal conjugate vaccine for children), and tuberculosis.

External links

• World Pneumonia Day