Typical Bacterial Pneumonia – Causes, Symptoms, Treatment

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Typical Bacterial Pneumonia/Pneumonia has been defined as an infection of the lung parenchyma. Rather than looking at it as a single disease, health care professionals must remember that pneumonia is an umbrella term for a group of syndromes caused by a variety of organisms resulting in varied manifestations and sequelae.

The severe form of acute lower respiratory tract infection that affects the pulmonary parenchyma in one or both lungs is known as pneumonia. It is a common disease and a potentially serious infectious disease with considerable morbidity and mortality. Pneumonia is the sixth leading cause of death and the only infectious disease in the top ten causes of death in the United States.

Pneumonia can be classified into 2 types based on how the infection is acquired:
  1. Community-acquired pneumonia (CAP): Most common type
  2. Nosocomial pneumonia
  • Hospital-acquired pneumonia (HAP)
  • Ventilator-associated pneumonia (VAP)
  • Healthcare-associated pneumonia (HCAP)

Community-acquired¬†pneumonia¬†is diagnosed in non-hospitalized patients or a¬†previously ambulatory patient within 48 hours after admission to the hospital. CAP is further divided into “typical” and “atypical.”

HAP develops more than 48 hours after hospital admission. Patients who are mechanically ventilated for more than 48 hours after endotracheal intubation can develop pneumonia known as VAP. HCAP occurs in ambulatory patients who are not hospitalized and have had extensive healthcare contact within the last 3 months.

Lobar Pneumonia

Lobar pneumonia is diffuse consolidation involving the entire lobe of the lung. Its evolvement can be broken down into 4 stages as follows

  • Congestion ¬†This stage is characterized by grossly heavy and boggy appearing lung tissue, diffuse congestion, vascular engorgement, and the accumulation of alveolar fluid rich in infective organisms. There are few red blood cells (RBC) and neutrophils at this stage.
  • Red hepatization ¬†Marked infiltration of red blood cells, neutrophils, and fibrin into the alveolar fluid is seen. Grossly, the lungs appear red and firm akin to a liver, hence the term hepatization.
  • Gray hepatization –¬†The RBC break down¬†and is associated with fibrinopurulent exudates causing a red to gray color transformation.
  • Resolution ¬†Characterized by clearing of the exudates by resident macrophages with or without residual scar tissue formation.

Bronchopneumonia

Bronchopneumonia is characterized by suppurative inflammation localized in patches around bronchi which may or may not be localized to a single lobe of the lung.

Causes of Typical Bacterial Pneumonia

Pneumonia occurs secondary to airborne infection which includes bacteria, viruses, fungi, parasites, among others.

The typical bacteria which cause pneumonia are Streptococcus pneumoniae, Staphylococcus aureus, Group A Streptococcus, Klebsiella pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, anaerobes, and gram-negative organisms. These organisms can be easily cultured on standard media or seen on Gram stain, unlike atypical organisms.

Streptococcus pneumoniae is the most commonly identified bacterial cause of CAP in all age groups worldwide. Methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli, and other Enterobacteriaceae are the predominant causes of HAP, VAP, and HCAP.

Although it is not necessary to have a predisposing condition to acquire pneumonia, having such factors makes a person more likely to develop lung infection. Any condition or disease that impairs the host immune response, for example, older age (older than 65 years), immunosuppression, diabetes, cystic fibrosis, lung cancer, among others. Conditions that increase the risk of macro- or micro-aspiration include stroke, seizures, anesthesia, drug intoxication. Cigarette smoking, alcoholism, malnutrition, obstruction of bronchi from tumors are other common predisposing conditions.

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Community-Acquired Pneumonia

Bacterial causes

They have been classically studied under the subheadings “typical” and “atypical” organisms in terms of ease of culture positivity. Common typical organisms include¬†Pneumococcus,¬†Haemophilus influenzae,¬†Moraxella catarrhalis, Group A¬†Streptococcus, and other aerobic and anaerobic gram-negative organisms. Atypical organisms commonly seen in clinical practice include¬†Legionella,¬†Mycoplasma,¬†Chlamydia, among others.¬†In the United States, the most common bacterial causes of CAP include¬†Streptococcus pneumoniae,¬†Staphylococcus aureus,¬†Mycoplasma pneumoniae, and gram-negative enteric bacilli.

Viral causes

It is often observed that viral species colonize nasopharynx of patients with CAP. Whether they are the primary cause or contribute to the pathogenesis by secondary bacterial causes is still being investigated. However, some of the most frequent viral agents implicated in CAP in the United States include the influenza virus followed by a respiratory syncytial virus, parainfluenza virus, and adenoviruses.

Fungal causes

Fungal infections are usually implicated in patients with certain predisposing immunocompromised states like HIV and organ transplant recipients, among others. However, often overlooked, some fungal species can cause pneumonia in immunocompetent individuals which results in a delay in diagnosis and leads to unfavorable outcomes. The 3 commonest ones in North America include Histoplasma, Blastomyces, and Coccidioides. 

Hospital-Acquired Pneumonia and Ventilator-Associated Pneumonia

There is considerable overlap in the etiologic agents in non-ventilated hospitalized patients and ventilated patients with pneumonia, and it is, therefore, appropriate to consider them together. These include:

  • Gram-negative bacilli like¬†Escherichia coli,¬†Pseudomonas Aerugenosa,¬†Acinetobacter, and¬†Enterobacter¬†among others
  • Gram-positive cocci like¬†Staphylococcus aureus;¬†both Methicillin-sensitive and resistant, although the latter is more prevalent
  • Other viruses and fungi that are more prevalent in immunocompromised and severely ill patients.

Symptoms Of Typical Bacterial Pneumonia

Symptoms of pneumonia caused by bacteria usually come on quickly. They may include:

Diagnosis of Typical Bacterial Pneumonia

Histopathology

Based on the area of the lung involved, pneumonia can be classified histologically into lobular, lobar, bronchopneumonia, and interstitial. The major types of acute bacterial pneumonia include:

  • Bronchopneumonia ¬†A descending infection started around the bronchi and bronchioles, which then spreads locally into the¬†lungs. Lower lobes are usually involved. Patchy areas of consolidation which represents neutrophil collection in the alveoli and bronchi.
  • Lobar pneumonia ¬†Acute exudative inflammation of the entire lobe. Uniform consolidation with a complete or near-complete consolidation of a lobe of a lung. The majority of these cases are caused by Streptococcus pneumonia.
Lobar pneumonia has 4 classical stages of inflammatory response if left untreated, namely
  • Congestion/consolidation – in the first 24 hours in which the lungs are heavy, red, and, boggy. Microscopically characterized by vascular engorgement and intra-alveolar edema. Many bacteria and few neutrophils are present.
  • Red hepatization/early consolidation – begins 2 to 3 days after consolidation and lasts for 2 to 4 days and named because of firm liver-like consistency. The affected lung is red-pink, dry, granular and, airless. Fibrin strands replace the edema fluid of the previous phase. Microscopically marked cellular exudate of neutrophils with some showing ingested bacteria, extravasation of erythrocytes, desquamated epithelial cells, and fibrin within the alveoli are seen. The alveolar septa become less prominent because of the exudate.
  • Grey hepatization/late consolidation – occurs 2 to 3 days following red hepatization and lasts for 4 to 8 days. The lung appears gray with liver-like consistency due to fibrinopurulent exudate, progressive disintegration of red blood cells, and hemosiderin. The macrophages begin to appear.
  • Resolution and restoration – of the pulmonary architecture start by the eighth day. The enzymatic action begins centrally and spreads peripherally which liquefies the previous solid fibrinous content and eventually restores aeration. Macrophages are the predominant cells which contain engulfed neutrophils and debris.

History and Physical

The signs and symptoms vary according to disease severity. The common symptoms of bacterial pneumonia include fever, cough, sputum production (may or may not be present). The color and quality of sputum provide the clue to microbiological etiology. Bacterial pneumonia mostly presents with mucopurulent sputum.

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Pleuritic chest pain due to localized inflammation of pleura can be seen with any kind of pneumonia but, is more common with lobar pneumonia. Constitutional symptoms such as fatigue, headache, myalgia, and arthralgias can also be seen.

Severe pneumonia can lead to dyspnea and shortness of breath. In severe cases, confusion, sepsis, and multi-organ failure can also manifest.

Tachypnea, increased vocal fremitus, egophony (E to A changes), dullness to percussion are the major clinical signs depending on the degree of consolidation and presence/absence of pleural effusion. Chest auscultation reveals crackles, rales, bronchial breath sounds.

The respiratory rate closely correlates with the degree of oxygenation and, therefore essential in determining the severity. Hypoxia is seen in severe pneumonia, which leads to hyperventilation.

Evaluation

To start with the evaluation of any pneumonia, clinical suspicion based on careful patient history and physical exam should always be followed by chest radiography which is the most important initial test.

  • Chest x-ray – not only shows the presence of the disease and demonstrates pulmonary infiltrate, but also provides the clue to the diagnosis whether its lobar, interstitial, unilateral or bilateral. Typical bacterial pneumonia is usually lobar pneumonia with para-pneumonic pleural effusions. However, a chest x-ray cannot reliably differentiate bacterial from a non-bacterial cause. When the labs and clinical features are positive, a positive chest radiograph is considered a gold standard for the diagnosis of pneumonia. Although computed tomography (CT) is a more reliable and accurate test, its use is limited due to relatively high radiation exposure and high cost. It can sometimes be done with high clinical syndrome favoring pneumonia with a negative chest x-ray. In a hospitalized patient with high clinical suspicion and negative radiograph, empiric presumptive antibiotic treatment should be started followed by a repeat chest x-ray after 24 to 48 hours.
  • Complete blood count (CBC) – with differentials, inflammatory biomarkers ESR, and acute phase reactants are indicated to confirm the evidence of inflammation and assess severity. Leukocytosis with a leftward shift is a major blood test abnormality whereas leukopenia can occur and points towards poor prognosis.
  • Sputum Gram stain and culture – should be done next if lobar pneumonia is suspected. The most specific diagnostic test for lobar pneumonia is a sputum culture. It is very important to identify the cause of proper treatment. It is preferable to test for influenza during the winter months as the combination of influenza and pneumonia is fatal.
  • CURB-65 and pneumonia – severity index help in the stratification of the patients and to determine if the patient needs hospitalization for treatment.
  • Routine diagnostic tests – are optional for outpatients with pneumonia, but hospitalized patients should undergo sputum culture, blood culture, and/or urine antigen testing preferably before the institution of antibiotic therapy.
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Thoracocentesis, bronchoscopy, pleural biopsy, or pleural fluid culture are invasive tests and are carried out very occasionally. An open lung biopsy is the ultimate specific diagnostic test.

Treatment of Typical Bacterial Pneumonia

The treatment depends on the severity of the disease. It is important to determine whether the patient needs to be treated inpatient or as an outpatient. CURB-65 pneumonia severity score or expanded CURB-65 can be used to stratify patients. One point for each factor which includes:

  • Confusion
  • Uremia (BUN greater than 20 mg/dL
  • Respiratory rate greater than 30 per minute
  • Hypotension (SBP less than 90 and DBP less than 60)
  • Age¬†older than more than 65 years

Patients with comorbid conditions such as renal disease, liver disease, cancer, chronic lung disease usually do better with inpatient treatment with IV medications.

A CURB-65 score of greater than or equal to 2 is an indication for hospitalization. A score of greater than or equal to 4 is an indication for an intensive care unit (ICU) admission and more intense therapy.

Depending on the clinical response, the therapy is indicated for 5 to 7 days. A favorable clinical response is the resolution of tachypnea, tachycardia, hypotension; absence of fever for more than 48 hours. In case of delayed response, the therapy should be extended.

Empiric therapy recommended for the following

  • Outpatient/non-hospitalized patient management Empiric therapy is almost always successful and usually testing is not required. In patients with no comorbidity, monotherapy with macrolides, such as azithromycin and clarithromycin are the first choice. Alternatively, newer fluoroquinolones like levofloxacin, moxifloxacin, or gemifloxacin can be used. The therapy is targeted against mycoplasma and chlamydia pneumonia which are the common causes of less¬†severe CAP. Patients with comorbid conditions (chronic lung or heart disease, diabetes, smoking, HIV, among others) do well with newer fluoroquinolones alone or with a combination of beta-lactam and a macrolide.
  • Inpatient non-ICU management ¬†The recommended therapy includes newer fluoroquinolones alone or a combination of beta-lactam/second or third-generation cephalosporin and a macrolide.
  • Inpatient ICU management – The recommended therapy is a combination of macrolide/newer fluoroquinolone and a beta-lactam. Ampicillin-sulbactam or ertapenem can be used in patients with a risk of aspiration. If there is a risk of Pseudomonas infection, a combination of anti-pseudomonal beta-lactam with an anti-pseudomonal fluoroquinolone is indicated. For MRSA, vancomycin or linezolid should be added. In case of complications such as empyema, chest tube drainage is required. Surgical decortication is needed in the case of multiple locations.

All hospitalized patients who test positive for the influenza virus must be treated with oseltamivir irrespective of the onset of illness.

Once the exact cause is determined, specific therapy should be initiated.

Differential Diagnosis

  • Asthma or reactive airway disease
  • Viral Pneumonia
  • Pneumonia, Fungal
  • Pneumonia, Atypical bacterial
  • Lung Abscess
  • Bronchiectasis
  • Bronchiolitis
  • Asthma
  • Acute and Chronic Bronchitis
  • Atelectasis
  • Croup
  • Respiratory distress syndrome
  • Aspiration of a¬†foreign body

Complications

References

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