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Image: “Pneumonia in chest X-ray” by Hellerhoff. License: CC BY-SA 3.0
Definition of Pneumonia
Pneumonia—an inflammation of the lungs with various causes
Pneumonia or (pulmonary inflammation) is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes or in the course of radiotherapy.
Classification of pneumonia
Classification of pneumonia in literature is not uniform and is determined either by the location of its occurrence, the site of infection, etiology or its underlying pathogenic causes.
The Primary Pneumonia ist pneumonia of a healthy lung with the Pathogens:
- Pneumococci
- Staphylococci
- Haemophilus influenzae
- Mycoplasma
- Chlamydia
- Legionella
- Adenovirus and parainfluenza viruses
The Secondary Pneumonia is pneumonia as a secondary infection or as a super propagated infection of the bronchi. Involved pathogens are:
- Herpes viruses
- Fungi
- Protozoa
- Anaerobes
Classification of pneumonia according to the site of infection
Since the germ reservoir varies from place to place, knowledge of the place of the infection can often be of immanent importance for the diagnosis and treatment. We, therefore, make the following distinctions:
Community-acquired pneumonia (CAP)
Pneumonia acquired outside of hospitals with the pathogens streptococcus pneumoniae, haemophilus influenzae, chlamydia pneumoniae, legionella.
Hospital-acquired pneumonia (HAP)
Pneumonia acquired during hospitalization with the pathogens Pseudomonas aeruginosa, enterobacter, E. coli, Proteus, Serratia, klebsiella pneumoniae.
Pneumonia under immunosuppression
Pneumonia due to congenital or acquired immune deficiencies. Common variable immunodeficiency (CVID): granulocyte macrophage defects and immunosuppressive therapy for HIV infection, neutropenia, organ transplantation.
Lobar pneumonia
Pneumonia of a single pulmonary lobe with possible involvement of the pleura.
Symptoms: fever, cough, dyspnea, tachypnea, rust brown sputum (red hepatization), hemoptysis, fever blisters. Involved pathogens are:
- Pneumococcus (Streptococcus pneumoniae)
- Staphylococcus
- Haemophilus influenzae
- Klebsiella
Interstitial pneumonia
Inflammation of large areas of the lung under the restriction of interstitial lung scaffold; symptoms: cough, tachypnea, dyspnea. Involved pathogens are viruses, intracellular proliferating bacteria such as chlamydia, mycoplasma, legionella.
Bronchial pneumonia
Propagated from bacterial bronchitis, usually only affecting individual segments of a pulmonary lobe. Involved pathogens are bacteria.
Significant pathogenic causes for the occurrence of pneumonia are bacteria, viruses, and fungi. It is customary to conceptually combine typical pneumonia, which is caused by bacteria, with lobar pneumonia, therefore it is often referred to as typical lobar pneumonia in literature. The same applies to atypical pneumonia which is usually induced virally or by a fungus and which is conceptually combined with interstitial pneumonia. An estimated 20 % of occurring pneumonia is atypical pneumonia.
Typical pneumonia
Acute inflammation, concerning one or more lung lobes. Symptoms are fever, chills, painful cough, purulent mucus, possibly pleural effusion. Involved pathogens are pneumococcus (Streptococcus pneumoniae), staphylococcus, klebsiella, pseudomonas, proteus.
Atypical pneumonia
Inflammation of the interstitial lung tissue with the symptoms possible moderate fever, dry cough. Involved pathogens are viruses, chlamydia, rickettsia, mycoplasma, legionella, pneumocystis jirovecii, coxiella burnetii.
Classification of pneumonia according to its etiology
Sometimes pneumonia is defined in terms of its etiology. Possible etiological causes are:
- Etiological definition of pneumonia
- Pneumonia in chronic lung disease
- Pneumonia in other underlying diseases
- Pneumonia after aspiration
- Pneumonia due to allergic causes
Epidemiology of Pneumonia
Pneumonia, the second leading infectious disease worldwide
With community-acquired pneumonia being the second most commonly detected infectious disease worldwide, it is of great economic as well as socio-economic importance. In Germany, there are approximately 400,000 to 600,000 cases per year. The incidence rate is estimated to be approximately one to eleven cases per 1,000 inhabitants per year while the rate in retirement homes is much higher and rockets to 68 to 114 cases per 1,000 people.
The main pathogens are:
- Pneumococci (25—45 %)
- Haemophilus influenzae (5—20 %)
- Mycoplasma pneumoniae (5—15 %), the most common pneumonia pathogen in adolescents and young adults
- Viruses, fungi and other bacteria (5—25 %)
Etiology of Pneumonia
The most common causes of pneumonia
Common causes of pneumonia generally are pathological changes of the airways and lung tissue, local or systemic immunodeficiency, bed confinement and age.
Image: “pulmonary fibrosis” by National Heart Lung and Blood Institute (NIH). License: Public Domain
The main pulmonary pre-existing conditions that increase the risk of pneumonia are:
Other predisposing factors that increase the risk of pneumonia due to general immune deficiency are:
- HIV infection
- Leukemia
- Lymphomas
- Tumors (lung cancer)
- Therapy with corticosteroids and immunosuppressants
- Diabetes mellitus
- Renal insufficiency
In addition to pre-existing medical conditions that weaken the immune system, often other trigger events favor the emergence of pneumonia:
- Aspiration of gastric content and food
- Pulmonary embolism
- Pulmonary congestion with left ventricular failure
- Basal hypoventilation (bed confinement/shallow breathing)
Pathogenesis of Pneumonia
Pathogenesis of typical lobar pneumonia
Approximately 90 % of all pneumonia cases are caused by bacteria. Untreated, the majority of these cases display the course of typical lobar pneumonia. This usually starts acutely and suddenly, with chills and is followed by rapidly rising fever. Further symptoms that develop during the course are:
Fever Chart pulse (red) and breathing (blue) in lobar pneumonia
- Painful cough
- Dyspnea
- Tachypnea
- Tachycardia
- Purulent sputum
- Pleural effusion
- Hemoptysis
Image: “Typical X-ray image of lobar pneumonia in the left upper lobe. The arrows point to the border of the lower lobe.” by Hellerhoff. License: CC BY-SA 3.0
In addition to these symptoms, the expected course of a typical case of lobar pneumonia is divided into three stages:
Stage 1: Engorgement (accumulation of serous fluid in the alveoli)
Stage 2: Red hepatization (russet colored sputum due to the admixture of blood)
Stage 3: Yellow hepatization (liquefaction of the secretion and subsequent resorption)
Pathogenesis of atypical interstitial pneumonia
Image: “AP chest x-ray of a patient with pneumocystis jiroveci pneumonia, showing reticular interstitial markings in all lung fields. Released into public domain on permission of patient.” by Samir. License: CC BY-SA 3.0
Image: “Histopathological image of pulmonary fibrosis representing usual interstitial pneumonia (UIP).” by KGH. License: CC BY-SA 3.0
Atypical pneumonia begins insidiously. A cough is dry. The patient complains of a headache and aching limbs with moderate fever. Overall, the symptoms of atypical interstitial pneumonia are less clear and acute than those of typical lobar pneumonia.
Diagnosis of Pneumonia
Clinic of pneumonia
Image: “Main symptoms of infectious pneumonia.” by Mikael Häggström. License: Public Domain
Primary, community-acquired pneumonia (CAP) is generally diagnosed clinically in uncomplicated cases. Physical examination shows:
- On percussion damping above the affected area
- Increased vocal fremitus in the affected area
- Bronchial respiration
- Fine bubble rales
- In case of additional, accompanying pleuritis: coarse bubbling, bronchial sounds
Cases of severe, secondary, hospital-acquired pneumonia (HAP) usually require targeted therapeutic intervention consisting of a three-step approach of the clinic, laboratory tests, and pathogen detection. Pathogen detection is achieved from sputum. Apart from a possibly intensified breathing sound (bronchial breathing), little diagnostic evidence can be detected clinically. The sensitivity and specificity only are around 60 %. Typical laboratory parameters are:
CRP↑
BSG↑
leucocytes ↑
Chest X-ray for diagnosis of pneumonia
Image: “Pneumonia in chest X-ray” by Hellerhoff. License: CC BY-SA 3.0
The most important diagnostic measure to diagnose pneumonia is the chest X-ray. For a detailed investigation of pneumonia, two X-ray images are made. Less ventilated lung areas show up light in the radiograph. Amongst other things, this can be observed with massive immigration of leukocytes (infiltration).
Typical lobar pneumonia can be characterized by homogeneous shading, possibly several lobes or lobe segments in a row affected simultaneously. The atypical interstitial pneumonia has increased interstitial markings; distributed throughout the lungs or accentuated nuclear shadowing.
Bronchial pneumonia can be characterized by scattered focal, confluent infiltrates possibly scattered throughout the lungs and the alveolar pneumonia is marked through alveolar space filled with exudate.
Further diagnostic measures for pneumonia
If the findings remain unclear after the clinic, laboratory, chest X-ray and pathogen detection, the following diagnostic measures can be added:
- Sonogram for determination of pleural effusion
- Computer tomography for a more precise evaluation of the location and extent of inflammation
Image: “Computed tomography (CT) scan of chest showing bilateral pneumonia with abscesses, effusions, and caverns. 37-year-old male.” by Christaras A. License: CC BY-SA 3.0
- A lung perfusion scintigraphy to study the blood flow to the lungs for suspected pulmonary embolism
- A bronchoscopy to detect foreign bodies or tumors in the airways
- A bronchial lavage for targeted sampling of pathogenic liquids
Differential Diagnosis
Similar diseases to pneumonia
The following diseases can display similar symptoms and test results to pneumonia:
- Bronchial carcinoma
- Pulmonary tuberculosis
- Pulmonary embolism with infarction
- Pulmonary fibrosis
Therapy of Pneumonia
Different therapeutic strategies for the treatment of pneumonia
Treatment of pneumonia depends on the respective underlying pathogens, the severity of the disease and individual risk factors to be assessed for each patient such as age, comorbidities, and previous antibiotic treatments. If risk factors are present, the patient should be hospitalized, in severe clinical cases possibly in the ICU.
Therapeutic measures for community-acquired pneumonia (CAP)
Since the majority of pneumonia has a bacterial origin, community-acquired pneumonia is treated with a carefully selected antibiotic therapy without prior pathogen detection. Uncomplicated cases are usually treated with aminopenicillins. The duration of therapy lies around 7—10 days.
Therapeutic measures in hospital-acquired pneumonia (HAP)
Prior to the initiation of antibiotic therapy, pathogen detection is essential in hospital-acquired pneumonia. Depending on the severity of the clinical picture, a calculated antibiotic therapy can subsequently be introduced intravenously, which upon a characterization of the pathogen, can then be adapted if necessary. The duration of the therapy lies around 7 days.
Complications of Pneumonia
In case of late treatment or protraction, pneumonia can lead to serious complications that affect the pulmonary parenchyma or even go beyond that and affect the entire organism. Frequently affected body parts are blood, brain, and heart. One of the major complications is a lung abscess.
Lung abscesses as a complication of pneumonia
A lung abscess is a purulent fusion of the lung tissue (necrosis). Pneumonia pathogens that frequently cause a lung abscess are:
- Staphylococcus
- Klebsiella
- Anaerobes
Other possible non-infectious causes for the formation of a lung abscess are:
- Aspiration of foreign bodies or gastric acid
- Local reduced perfusion, e.g. due to a pulmonary infarction
- Bronchial carcinoma
The clinic of lung abscesses is dominated by symptoms such as cough, dyspnea, fever and chest pain. If the abscess collapses into a bronchus this is clinically displayed clearly in a sudden occurrence of severe purulent sputum (two-layer sputum). The ejected material is partly purulent, partly putrid. Hence, the evil putrid mouth-and breath odor which can occur concomitantly (halitosis).
Therapeutically, a calculated long-term treatment with antibiotics and if appropriate, simultaneous postural drainage or direct abscess drainage should be performed. In the worst case, surgical intervention is required (resection).
More complications of pneumonia to be aware of
- Pleurisy
- Pleural empyema
- Pneumogenic sepsis
- Acute progressive respiratory failure (ARDS)
- An endogenous inflammatory response of the whole organism (SIRS)
- Pneumatoceles
If signs of pneumonia are still visible in the X-ray after six to eight weeks, it must be assumed that the disease has become chronic. In general, this usually affects patients with a weak immune system and existing chronic diseases.
Prognosis of Pneumonia
Different types of pneumonia have different prognoses
The prognosis highly depends on the type of pneumonia. While primary community-acquired pneumonia has a good prognosis with a fatality rate below 1 %, the mortality rate in secondary hospital-acquired pneumonia is about 20 %. Cases of pneumonia that require hospitalization have a mortality rate of > 10 %.
Prevention
Pneumococcal vaccination for pneumonia prevention
Risk groups such as infants, diabetics, patients with the weakened immune system, patients older than 65 with recurrent respiratory diseases and patients after splenectomy are advised to get vaccinated against pneumococcus.
Flu vaccination for the prevention of pneumonia
An annual flu shot is recommended for people over 60 years who are in close contact with many people occupationally (nurses, kindergarten staff, retailers). Furthermore, people with the following underlying diseases are encouraged to get a basic flu shot:
- People with cardiovascular diseases such as hypertension or angina
- People with lung disease such as asthma or chronic bronchitis
- People with metabolic disorders such as diabetes mellitus
- People with kidney disease
- HIV-infected patients
- Leukemia patients
Other preventive measures against pneumonia:
- Haemophilus influenza vaccination
- Strict abstinence from smoking
- Wearing respirators in occupations with exposure to dust
Review Questions
The answers are below the references.
1. In microscopic slides of the sputum of suspected pneumonia patients, rounded up lancet-shaped bacteria, mounted in pairs, is often observed. It most likely involves:
- Treponemes
- Vibrios
- Clostridia
- Staphylococci
- Pneumococci
2. Mycoplasma is…
- …bacteria without cell walls.
- …capsule-forming bacteria.
- …animal viruses.
- …bacteria formed under the influence of penicillin.
- …bacteria treated with lysozyme.
3. Alveolar epithelial…
- …has kinocilia.
- …is superimposed by surfactant on the surface.
- …has goblet cells, amongst others.
- …is underlaid by smooth muscle.
- …cannot regenerate.
