Bacterial Pneumonia

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What is Bacterial Pneumonia?

Bacterial Pneumonia is an infection of lung Parenchyma. Lung parenchyma consists of functional part of lung tissue, which consists of alveolar tissue with respiratory bronchioles, alveolar ducts and terminal bronchioles.

In top ten causes of death in United States, Pneumonia is the only infectious cause. It is sixth leading cause of death in US

Pathophysiology of Bacterial Pneumonia:

Bacteria causing pneumonia mostly have three routes of entry to lungs

1-Through blood stream (If there are infections to other parts of body
3-Bacteria living in upper respiratory tract being continuously inhaled and reaches alveolar tissue.

Once inside the lung tissue, the foreign body (Bacteria) causes the immune system to respond via neutrophils. Neutrophils kills the bacteria by engulfing it and release chemicals, enzymes and cytokines which results in signs and symptoms like fever, chills and weakness. The enzymes released by neutrophils, killed bacteria causes leakage of fluid from surrounding blood vessels into the alveoli resulting in impaired oxygen exchange and thus resulting in breathlessness.

From lungs bacteria can spread into blood stream causing septic shock damaging multiple organs of the body or can reach into plural cavity (area between lungs and chest wall)

Risk Factors for Bacterial Pneumonia

It is not necessary to have a predisposing condition for bacterial pneumonia to occur, but there are few instances when some conditions makes it easier for bacteria to infect the lung tissue.

Cigarette Smoking
Obstruction of bronchioles by tumor
Decreased Immunity

Agents Causing Bacterial Pneumonia

Typical Agents- responsible for 40-60% of all cases 

Sterptococcus pneumoniae 

Atypical Agents- responsible for 10-30% of all cases of pneumonia


Pneumonia can be classified into two major groups depending upon the source of infection:

1- Community Acquired Bacterial Pneumonia : Number one cause is streptococcus pneumoniae in all age groups other than in children less than 5 years of age where virus is the most common cause

2-Hospital Acquired Pneumonia: Mostly from "Gram Negative Bacilli" like E.coli, pseudomonas and klebsiella or gram positive bacilli like staph aureus

Signs and Symptoms of Bacterial Pneumonia:

Patients with pneumonia usually present with:

Sputum Production- Rusty, currant jelly
Breathlessness (If pneumonia is severe)
Chest Pain

Bacterial Pneumonia caused by atypical organism might present without productive cough (dry cough).

Legionella associated bacterial pneumonia may present with CNS (brain) involvement causing confusion and headache with loose stools and abdominal pain.

Diagnosis Of bacterial Pneumonia

Chest X ray is the most important test in diagnosing bacterial pneumonia. X-ray not only helps in diagnosis but also give a clue about the organism depending upon the involvement of lung tissue.

Lobar- Limited to one lobe with or without pleural effusion (Typical Pneumonia by strep pneumoniae)

Interstetial and bilateral- caused by Mycoplasma, chalmydia, coxiella and sometimes legionella.

Sputum culture is the most specific diagnostic test for lobar pneumonia, while sometimes more invasive tests are required to confirm the diagnosis of bacterial pneumonia especially if caused by atypical agents.

Antibiotics are the mainstay for the treatment of the Bacterial Pneumonia

Hospitalization is required or not depends upon the severity of the disease. there are several markers of severity like

Oxygen Saturation of Hemoglobin
Partial Pressure of oxygen
Respiratory rate
Low Blood pressure
Confusion, disorientation
Rapid pulse

Treatment of Community Acquired Bacterial Pneumonia

If hospitalization is not required community acquired pneumonia is usually treated with macrolides (azithromycin, clarithromycin) or new generation fluroquinolones (Levofloxacin, moxifloxacin, gatifloxacin)

If patient is admitted in the hospital the antibiotic of choice is new generation fluroquinolones (Levofloxacin, moxifloxacin, gatifloxacin) or 2nd/3rd generation cephalosporins (Cefuroxime, ceftriaxone) with macrolide (Azithromycin, clarithromycin) or doxycycline.

Treatment of Hospital Acquired Bacterial Pneumonia

As discussed during hospital stay pneumonia can be caused by gram negative bacilli like pseudomonas, klebsiella , E.coli or gram positive bacilli like methicillin resistant staphylococcus aureus (MRSA).

Emperical therapy is usually with :

3rd generation cephalosporins with antipseudomonal activity like ceftazidime/cefortaxime or imipenem or piperacillin/tazobactam. Coverage for MRSA with vancomycin or linezolid.

Aminoglycosides (gentamycin, tobramycin, amikacin) are usually added for synergy.