Bacterial Pneumonia – Causes, Symptoms, Treatments

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Atypical Bacterial Pneumonia /The word “pneumonia” takes its origin from the ancient Greek word “pneumon,” which means “lung,” so the word “pneumonia” becomes “lung disease.” Medically it is an inflammation of one or both lungs’ parenchyma that is more often, but not always, caused by infections. The many causes of pneumonia include bacteria, viruses, fungi, and parasites. This article will focus on bacterial pneumonia, as it is the major cause of morbidity and mortality. According to the new classification of pneumonia, there are four categories: community-acquired (CAP), hospital-acquired (HAP), healthcare-associated (HCAP) and ventilator-associated pneumonia (VAP). 

Pneumonia is a lower respiratory tract infection, specifically involving the pulmonary parenchyma. Viruses, fungi, and bacteria can cause pneumonia. The severity of pneumonia can range from mild to life-threatening, with uncomplicated disease resolving with outpatient antibiotics and complicated cases progressing to septic shock, acute respiratory distress syndrome (ARDS) and death. It affects all age groups, accounts for over 2 million emergency visits annually, and is a leading cause of mortality in both adults and children. Atypical micro-organisms are known to cause a disproportionate disease burden in children and adolescents. Atypical organisms are difficult to culture.  They present subacutely and with progressive constitutional symptoms.

Atypical pneumonia

Typical pneumonia generally begins with a sudden high fever and chills and then coughing with phlegm coming later.

Atypical pneumonia is caused by other germs, which are also referred to as “atypical.” Older people, in particular, have fewer or slightly different symptoms if they have atypical pneumonia: It then starts off rather slowly with a mild fever and/or headache and aching limbs. Rather than coughing with phlegm, they have a dry, tickly cough.

Atypical symptoms don’t mean that the lungs are less severely inflamed or that the disease will take a milder course though.

Upper, middle and lower lobe pneumonia

X-rays play an important role in distinguishing between these types: the term lobar pneumonia is used if an entire lung lobe is visibly inflamed. Depending on which lung lobe is affected, the pneumonia is referred to as upper, middle or lower lobe pneumonia.

If there are several multi-lobe focal inflammations in the lungs, the term focal pneumonia is used. Some people use the term bronchopneumonia if the focal inflammations started in inflamed airways ().

Types of Bacterial Pneumonia

  • CAP: The acute infection of lung tissue in a patient who has acquired it from the community or within 48 hours of the hospital admission.
  • HAP: The acute infection of lung tissue in a non-intubated patient that develops after 48 hours of hospitalization.
  • VAP: A type of nosocomial infection of lung tissue that usually develops 48 hours or longer after intubation for mechanical ventilation.
  • HCAP: The acute infection of lung tissue acquired from healthcare facilities such as nursing homes, dialysis centers, and outpatient clinics or from a patient with a history of hospitalization within the past three months.

Some articles include both HAP and VAP under the category of HCAP, so defining HCAP is problematic and controversial.

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Causes of

Community-acquired pneumonia can be caused by an extensive list of agents that include bacteria, viruses, fungi, and parasites, but this article will focus on bacterial pneumonia and its causes. Bacteria have classically been categorized into two divisions on the basis of etiology, “typical” and “atypical” organisms. Typical organisms can be cultured on standard media or seen on Gram stain, but atypical organisms do not have such properties.

  • Typical pneumonia refers to pneumonia caused by Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, Group A streptococci, Moraxella catarrhalis, anaerobes, and aerobic gram-negative bacteria.
  • Atypical pneumonia is mostly caused by Legionella, Mycoplasma pneumoniae, Chlamydia pneumoniae, and Chlamydia psittaci.
  • Congestion – In this stage, pulmonary parenchyma is not fully consolidated, and microscopically, the alveoli have serous exudates, pathogens, few neutrophils, and macrophages.
  • Red hepatization – In this stage, the lobe becomes consolidated, firm, and liver-like. Microscopically, there is an addition of fibrin along with serous exudate, pathogens, neutrophils, and macrophages. The capillaries are congested, and the alveolar walls are thickened.
  • Gray hepatization – The lobe is still liver-like inconsistency but gray in color due to suppurative and exudate-filled alveoli.
  • Resolution – After a week, it starts resolving as lymphatic drainage or a productive cough clears the exudate.

While taking the history, it is crucial to explore the patient’s potential exposures, risks of aspiration, host factors, and presenting symptoms.

Exposure – A detailed history of possible exposures should be sought as it can help in establishing the potential etiologies. The following are some associations of exposures and etiologies of bacterial pneumonia:

  • Contaminated air-conditioning and water systems may cause legionella pneumonia
  • Crowded places, such as jails, shelters, etc. expose a person to streptococcus pneumonia, mycobacteria, mycoplasma, and chlamydia
  • Exposures to several animals, such as cats sheep, and cattle may lead to infection with Coxiella burnetii
  • Some birds, such as chickens, turkeys, and ducks, can expose a person to Chlamydia psittaci.

Risks of Aspiration – Patients who have an increased risk of aspiration are more prone to develop pneumonia secondary to aspiration. Associated risks are:

  • Altered mentation
  • Drug abuse
  • Dysphagia
  • Gastroesophageal reflux disease (GERD)
  • Alcoholism
  • Seizure disorder

Host mechanisms – It is of utmost importance to explore a detailed history to find clues towards the etiology of pneumonia. For instance, a history of asthma, COPD, smoking, and immunocompromised status can be indicative of H influenza infection. H influenza most commonly appears in the winter season. Similarly, social, sexual, medication and family history can all be useful in determining the cause of illness.

Features in the history of bacterial pneumonia may vary from indolent to fulminant. Clinical manifestation includes both constitutional findings and findings due to damage to the lung and related tissue. The following are significant history findings:

  • Fever with tachycardia and/or chills and sweats.
  • The cough may be either nonproductive or productive with mucoid, purulent or blood-tinged sputum.
  • Pleuritic chest pain if the pleura is involved.
  • Shortness of breath with normal daily routine work.
  • Other symptoms include fatigue, headache, myalgia, and arthralgia.

For unbeknownst reasons, the presence of rigors is more often indicative of pneumococcal pneumonia than other bacterial pathogens. 

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The presence of productive cough is the most common and significant presenting symptom. Some bacterial causes have particular manifestation, such as:

  • S pneumoniae – Rust-colored sputum
  • Pseudomonas, Hemophilus – Green sputum
  • Klebsiella – Red currant-jelly sputum
  • Anaerobes – foul-smelling and bad-tasting sputum

Atypical pneumonia presents with pulmonary and extra-pulmonary manifestations, such as Legionella pneumonia, often presents with altered mentation and gastrointestinal symptoms.

Physical findings also vary from patient to patient and mainly depend on the severity of lung consolidation, the type of organism, the extent of the infection, host factors, and existence or nonexistence of pleural effusion. The following are major clinical findings:

  • Increased temperature (usually more than 38 C or 100.4 F)
  • Decreased temperature (less than 35 C or 95 F)
  • Increased respiratory rate (more than 18 breaths/min)
  • Increased heart rate (more than 100/min)
  • Bradycardia (less than 60/min)
  • Cyanosis
  • Percussion sounds vary from flat to dull
  • Tactile fremitus
  • Crackles, rales, and bronchial breath sounds are heard on auscultation
  • Tracheal deviation
  • Lymphadenopathy
  • Pleural rub
  • Egophony

Confusion manifests earlier in older patients. A critically ill patient may present with sepsis or multi-organ failure.

Some examination findings are specific for certain etiologies, such as:

  • Bradycardia – Legionella
  • Dental illnesses – Anaerobes
  • Impaired gag reflex – Aspiration pneumonia
  • Cutaneous nodules – Nocardiosis
  • Bullous myringitis – Mycoplasma.

The approach to evaluate and diagnose pneumonia depends on the clinical status, laboratory parameters, and radiological evaluation.

  • Clinical Evaluation – It includes taking a careful patient history and performing a thorough physical examination to judge the clinical signs and symptoms mentioned above.
  • Laboratory Evaluation – This includes lab values such as complete blood count with differentials, inflammatory biomarkers like ESR and C-reactive protein, blood cultures, sputum analysis or Gram staining and/or urine antigen testing or polymerase chain reaction for nucleic acid detection of certain bacteria.
  • An arterial blood gas may reveal hypoxia and respiratory acidosis.
  • Pulse oximetry of less than 92% indicates severe hypoxia and elevated CRP predicts a serious infection.
  • Blood cultures should be obtained before administering antibiotics. Unfortunately, they are only positive in 40% of cases.
  • Sputum evaluation if good quality may reveal more than 25 WBC per low-power field and less than 10 squamous epithelial cells.
  • Some bacterial causes present with specific biochemical evidence, such as Legionella may present with hyponatremia and microhematuria.
  • Radiological Evaluation – It includes a chest x-ray as an initial imaging test and the finding of pulmonary infiltrates on plain film is considered as a gold standard for diagnosis when the lab and clinical features are supportive.
  • The chest x-ray may reveal a consolidation or parapneumonic effusion.
  • Chest CT is done for complex cases where the cause is not known.
  • Bronchoalveolar lavage is done in patients who are intubated and can provide samples for culture.


In all patients with bacterial pneumonia, empirical therapy should be started as soon as possible. The first step in treatment is a risk assessment to know whether the patient should be treated in an outpatient or inpatient setting. Cardiopulmonary conditions, age, and severity of symptoms affect risk for bacterial pneumonia, especially CAP.

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An expanded CURB-65 or CURB-65 pneumonia severity score can be used for risk quantification. It includes C = Confusion, U = Uremia (BUN greater than 20 mg/dL), R = Respiratory rate (greater than 30 per min), B = B.P (BP less than 90/60 mmHg) and age greater than 65 years. One point is scored for each of these risk factors. For a score of 0-1, outpatient treatment is advised. If the total score is 2 or more, it indicates medical ward admission. If the total score is 3 or more, it indicates ICU admission. Recommended therapy for different settings are as follows:

  • Outpatient Setting – For patients having comorbid conditions ( e.g., diabetes, malignancy, etc.), the regimen is fluoroquinolone or beta-lactams + macrolide. For patients with no comorbid conditions, macrolide or doxycycline can be used empirically. Testing is usually not performed as the empiric regimen is almost always successful.
  • Inpatient Setting (non-ICU) – Recommended therapy is fluoroquinolone or macrolide + beta-lactam.
  • Inpatient Setting (ICU) – Recommended therapy is beta-lactam + macrolide or beta-lactam + fluoroquinolone.
  • MRSA: Vancomycin or linezolid can be added.

After getting a culture-positive lab result, therapy should be altered according to the culture-specific pathogen. The patient also can benefit from smoking cessation, counseling, and vaccination for influenza and pneumococcus. All patients treated at home should be scheduled for a follow-up visit within 2 days to assess any complication of pneumonia. The role of corticosteroids remains controversial and may be used in patients who remain hypotensive with presumed adrenal insufficiency.

Other measures

  • Hydration
  • Chest physical therapy
  • Monitoring with pulse oximetry
  • Upright positioning
  • Respiratory therapy with bronchodilators
  • Mechanical support if patients are in respiratory distress
  • Nutrition
  • Early mobilization


The most common complications of bacterial pneumonia are respiratory failure, sepsis, multiorgan failure, coagulopathy, and exacerbation of preexisting comorbidities. Other potential complications of bacterial pneumonia include:

  • Lung fibrosis
  • Destruction of lung parenchyma
  • Necrotizing pneumonia
  • Cavitation
  • Empyema
  • Pulmonary abscess
  • Meningitis
  • Death


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