Community-acquired pneumonia

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Alejandro Lemor, M.D. [2]

Community-acquired pneumonia (CAP) is an infection of the lungs which occurs outside the hospital settings. It is the most common form of pneumonia and a major cause of morbidity and mortality. It often causes symptoms such as: breathing difficulties, fever, chest pains, and cough. Community-acquired pneumonia occurs when the alveoli becomes filled with fluid and cannot work effectively.Causes of CAP include: bacteria, viruses, fungi, and parasites. CAP can be diagnosed by its symptoms and physical examination alone, although x-rays, examinations of the sputum, and other tests are also often used. CAP is primarily treated with antibiotic medication. Some forms of CAP can be prevented by vaccination.

Sir William Osler, known as “the Father of Modern Medicine,” appreciated the morbidity and mortality of pneumonia, describing it as the “Captain of the Men of Death” in 1918. However, several key developments in the 1900s improved the outcome for those with pneumonia. With the arrival of penicillin and other antibiotics, modern surgical techniques, and intensive care in the twentieth century, mortality from pneumonia dropped precipitously in the developed world. Vaccination of infants against Haemophilus influenzae type b began in 1988 and led to a dramatic decline in cases shortly thereafter.^[1] Vaccination against Streptococcus pneumoniae in adults began in 1977, and it began in children during the year 2000; this resulted in a similar decline.^[2]

The lower respiratory tract is protected by different pulmonary defense mechanisms ^[3]. Community-acquired pneumonia connotes a breach of host defense mechanisms and/or an overwhelming inoculation of virulent infectious agents. Modes of transmission include: macro- or micro-aspiration, circulation, local spread, traumatic inoculation, and iatrogenic. Impaired immunity and inability to filter out pathogen increase the risk for developing pneumonia. Causative etiologies vary with age, immune status, geographical area, and comorbid conditions.

Community-acquired pneumonia can be caused by viral, bacterial, and fungal organisms. Causative etiology varies with age, immune status, epidemiologic background, and comorbidity. The most common cause of CAP in adult outpatients and inpatients is Streptococcus pneumoniae. Patients admitted to the intensive care unit tend to have more aggressive organisms such as Staphylococcus aureus and Gram-negative bacilli. Neonates are most susceptible to Group-B-Streptococcus (GBS) which causes approximately 50% of pneumonias in the first week of life. Children and elderly patients are more susceptible to viral infections as well atypical bacterial pneumonias (Mycoplasma, Chlamydia, Legionella).

Pneumonia should be differentiated from other non-infectious conditions that cause cough, fever, shortness of breath, tachypnea and lung infiltrates; such other conditions include: interstitial lung disease, CHF, cancer, and pulmonary emboli.

Pneumonia is the leading cause of death in children younger than 5 years of age worldwide. Both children and the elderly are at a higher risk of pneumonia complications. Developing countries have a higher mortality rate among children with pneumonia.

The risk factors of pneumonia include: smoking, age, immunosuppression, exposure to chemicals, and underlying lung disease.

Complications, including sepsis, respiratory failure, pleural effusion, and empyema, may occur despite appropriate antibiotic treatment. Complications are associated with bacterial pneumonia more frequently than they are with viral pneumonia. Most types of bacterial pneumonia can be cured within one to two weeks of using appropriate medication. Viral pneumonia may last longer, and mycoplasmal pneumonia may take four to six weeks to resolve completely. The eventual outcome of an episode of pneumonia depends on how ill the person is when first diagnosed.

CURB-65 is a clinical prediction rule that has been validated for predicting mortality in community-acquired pneumonia^[4] and infection of any site^[5]. The CURB-65 is based on the earlier CURB score^[6] and is recommended by the British Thoracic Society for the assessment of the severity of pneumonia.^[7]

The pneumonia severity index is a clinical prediction rule that medical practitioners can use to calculate the probability of morbidity and mortality among patients with community acquired pneumonia.^[8]

Common symptoms of pneumonia include: cough, fever, and difficulty breathing. Patients with CAP usually have a history of having close contact with similar symptoms.

Physical examination by a health care provider may reveal: fever,or sometimes low body temperature; an increased respiratory rate; low blood pressure; a fast heart rate; or a low oxygen saturation, which is the amount of oxygen in the blood as indicated by either pulse oximetry or blood gas analysis. People who are struggling to breathe, confused, or have cyanosis (blue-tinged skin) require immediate attention. A lack of normal breath sounds, the presence of crackling sounds (rales), or increased loudness of whispered speech (whispered pectoriloquy) can identify areas of the lung that are stiff and full of fluid; this is called “consolidation.” The examiner may feel the way the chest expands (palpation) and tap the chest wall (percussion) to further localize consolidation. The examiner may also palpate for increased vibration of the chest when speaking (tactile fremitus).^[9]

Laboratory findings, such as leukocytosis, are helpful for the diagnosis of bacterial pneumonia or the assessment of the patient’s status. Sputum samples need to be collected from every patient and gram staining and culture need to be performed in order to determine the exact pathogen causing the pneumonia. Other tests include: urine antigen test, PCR, C-reactive protein, and procalcitonin.

An important test for making a diagnosis of pneumonia is a chest x-ray. Chest x-rays can reveal areas of opacity (seen as white) which represent consolidation. Pneumonia is not always seen on x-rays, because the disease may either be in its initial stages or it involves a part of the lung not easily seen by an x-ray.

A chest CT scan is not routinely done in patients with pneumonia, but it is a diagnostic test that may be useful when a chest X-ray is not conclusive. CT findings may include: lobar consolidation, ground-glass oppacities, pleural effusion, lymphadenopathy, and tree-in-bud appearance.

In some cases, ultrasound is used to: diagnosis and follow-up a patient with pneumonia; perform a guided thoracocentesis; quantify the amount of pleural effusion.

Bronchoscopy with BAL (bronchoalveolar lavage) helps to identify certain uncommon pathogens that cause CAP and aid in the differential diagnosis to exclude non-infectious pneumonia.^[10]

Community acquired pneumonia treatment includes using the appropriate antibiotics and managing complications. An empirical therapy may be started while awaiting culture results. Once culture results are available, specific treatment may be started. Empiric therapy is classified according to severity, using the Pneumonia severity scale (PSI) and the CURB-65 score. Empirical therapy usually includes coverage for atypical and typical bacteria.

There are several ways of preventing infectious pneumonia. Appropriately treating underlying illnesses (such as AIDS), smoking cessation, vaccination against pneumococcal and influenza are the commonly used methods.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Sir William Osler, known as “the Father of Modern Medicine,” appreciated the morbidity and mortality of pneumonia, describing it as the “Captain of the Men of Death” in 1918. However, several key developments in the 1900s improved the outcome for those with pneumonia. With the arrival of: penicillin and other antibiotics; modern surgical techniques; and intensive care in the twentieth century, mortality from pneumonia dropped precipitously in the developed world. Vaccination of infants against Haemophilus influenzae type b began in 1988 and led to a dramatic decline in cases shortly thereafter.^[1] Vaccination against Streptococcus pneumoniae in adults began in 1977, and it began in children in 2000, resulting in a similar decline.^[2]

The symptoms of pneumonia were described by Hippocrates (c. 460 BC–380 BC) as:

However, Hippocrates himself referred to pneumonia as a disease “named by the ancients.” He also reported the results of surgical drainage of empyemas. Maimonides (1138–1204 AD) observed “The basic symptoms which occur in pneumonia and which are never lacking are as follows: acute fever, sticking pleuritic pain in the side, short rapid breaths, serrated pulse and cough.”^[3] This clinical description is quite similar to those found in modern textbooks, and it reflects the extent of medical knowledge during the Middle Ages into the 19th century.

Edwin Klebs was the first to see Bacteria in the airways of individuals who died from pneumonia in 1875.^[4] Initial work performed by Carl Friedländer^[5] and Albert Fränkel (1848-1916)^[6] in 1882 and 1884, respectively, identified the two common bacterial causes Streptococcus pneumoniae and Klebsiella pneumoniae. Friedländer’s initial work introduced the Gram stain, a fundamental laboratory test still used to identify and categorize bacteria. Christian Gram‘s paper describing the procedure in 1884 helped differentiate the two different bacteria and showed that pneumonia can be caused by more than one microorganism.^[7]

Pneumonia can be classified in several ways. Pathologists originally classified the different forms according to the anatomic changes that were found in the lungs during autopsies. As more became known about the microorganisms causing pneumonia, a microbiologic classification arose, and with the advent of x-rays, a radiological classification was created as well. Another important system of classification is the combined clinical classification, which combines factors such as: age, risk factors for certain microorganisms, the presence of underlying lung disease and underlying systemic disease, and whether or not the person has recently been hospitalized.

Initial descriptions of pneumonia focused on the anatomic or pathologic appearance of the lung, either by direct inspection during autopsy or by its appearance under a microscope.

• Lobar pneumonia is an infection that only involves a single lobe, or section, of a lung. Lobar pneumonia is often due to Streptococcus pneumoniae.

• Multilobar pneumonia involves more than one lobe, and it often causes a more severe illness.

• Interstitial pneumonia involves the areas in between the alveoli, and it may be called “interstitial pneumonitis“. It is more likely to be caused by viruses or by atypical bacteria.

The discovery of x-rays made it possible to determine the anatomic type of pneumonia without direct examination of the lungs during autopsy; this led to the development of a radiological classification. Early investigators distinguished between typical lobar pneumonia and atypical (e.g. Chlamydophila) or viral pneumonia using the location, distribution, and the appearance of the opacities they saw on chest X-rays. Certain X-ray findings can be used to help predict the course of illness, although it is not possible to clearly determine the microbiologic cause of a pneumonia with X-rays alone.

There is no established system for the classification of community-acquired pneumonia.

There is no established system for the classification of community-acquired pneumonia. However it can be categorized according to severity using the Pneumonia Severity Index (PSI) score and CURB-65 Score.

The PSI score is calculated using factors like age, demographic factors, comorbid illnesses, physical exam findings, radiographic and laboratory findings. Based on these factors, the severity of the disease can be classified into five risk categories ^[1]. Patients in Risk Class 1 to II can be managed in outpatient settings with oral antibiotics. Patients in Risk Class III can be managed in outpatient or inpatient settings after evaluation of risk factors. Patients in class IV and V should be admitted in the hospital for treatment. Risk Class I – III represents mortality of 0.1 – 0.9% whereas risk class V represent a 27% probability of mortality.

The CURB-65 score is also used to categorize patients according to disease severity ^[2]. It is calculated using the following factors:

New onset of Confusion.
Blood Urea Nitrogen > 7 mmol/L or > 20 mg/dL.
Respiratory Rate > 30 breaths/minute.
Blood pressure less than 90 mmHg SBP or less than 60 DBP.
Age > 65 years.

Patients can be treated as outpatient with a score of 0 – 1, whereas score of 3 – 5 requires hospitalization. CRB-65 is a simplified version of the score which is sometimes used in primary care settings for decision making. Hospitalization is recommended if one or more points are present.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Chetan Lokhande, M.B.B.S [2]

Because the lower respiratory tract is kept sterile by different pulmonary defense mechanisms,^[1] community-acquired pneumonia connotes a breach of host defense mechanisms and/or overwhelming inoculation of virulent infectious agents. Modes of transmission include: macro- or micro-aspiration, circulation, local spead, traumatic inoculation, or iatrogenic. Impaired immunity and inability to filter out pathogens, as well as microbial virulence factors that impede immune clearance may increase the risk of developing community acquired pneumonia.

The symptoms of CAP are the result of both, the invasion of the lungs by microorganisms and the immune system‘s response to the infection. The mechanisms of infection are quite different for viruses and the other microorganisms.

• Viruses must invade cells to reproduce. Typically, a virus reaches the lungs by travelling in droplets through the mouth and nose during inhalation. There, the virus invades the cells lining the airways and the alveoli.
• This invasion often leads to cell death, either through direct killing by the virus or by self-destruction through apoptosis.
• Further lung damage occurs when the immune system responds to the infection.
• White blood cells, in particular lymphocytes, activate a variety of chemicals (cytokines), which make fluid leak into the alveoli.
• The combination of cellular destruction and fluid-filled alveoli interrupts the transportation of oxygen into the bloodstream.
• In addition to their affect on the lungs, many viruses affect other organs; this can lead to illnesses that affect many different bodily functions.
• Viruses also make the body more susceptible to bacterial infection; for this reason, bacterial pneumonia often complicates viral CAP.

• Bacteria and fungi also typically enter the lung with inhalation, although they 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 constantly being inhaled into the alveoli.
• Once inside the alveoli, bacteria and fungi 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 they also release cytokines; this results in the general activation of the immune system. This causes the fever, chills, and fatigue which are common to CAP.
• The neutrophils, bacteria, and fluid leaked from surrounding blood vessels fill the alveoli and result in impaired oxygen transportation.
• Bacteria often travel from the lungs to the blood stream; this can often result in serious illness, such as septic shock, in which there is low blood pressure leading to damage to multiple parts of the body, including the brain, kidney, and heart.

• A variety of parasites can affect the lungs.
• In general, parasites enter the body through the skin or by ingestion.
• Once inside the body, these parasites travel to the lungs, most often through the blood.
• There, a similar combination of cellular destruction and immune response causes disruption of oxygen transportation.

Inhalation of aerosolized droplets that are 0.5 to 1 micrometer is the most common means of acquiring pneumonia. A few bacterial and viral infections are transmitted in this fashion. The lung can normally filter out particles that are between 0.5 to 2 micrometer in size by recruiting the alveolar macrophages.^[2]

Aspiration of oropharyngeal contents containing pathogenic microorganisms is one of the mechanisms for acquiring pneumonia. It most commonly occurs in in the average person during sleep, in an unconscious state, due to gastroesopahegeal reflux or impaired gag reflex and cough reflex.^[2]

Spread of an infection via the circulation may be a possible cause of pneumonia. Blood-borne pneumonia is seen more commonly in intravenous drug users particularly with gram-positive bacteria that may colonize the skin (i.e. Staphylococcus aureus). Gram-negative bacteria typically account for pneumonia in immunocompromised individuals.

Pneumonia can occur after a pulmonary procedure or a penetrating trauma to the lungs. A local spread of a hepatic abscess can also lead to pneumonia.

Several mechanisms have evolved to evade host defense mechanisms and facilitate microbial spread to establish an infection.

• Influenza viruses possess neuraminidase that cleaves sialic acid residues on the cell surface, which prevents viral aggregation and facilitates the propagation of viral particles.

• Chlamydophila pneumoniae induces complete paralysis of the respiratory cilia, which assists with the colonization of the respiratory epithelium.^[3]

• Mycoplasma pneumoniae produces a virulence factor with ADP-ribosylating activity that is responsible for airway cellular damage and mucociliary dysfunction.^[4]

• Haemophilus influenzae, Streptococcus pneumoniae, and Neisseria meningitidis produce proteases that cleave mucosal IgA.

• Streptococcus pneumoniae possesses pneumolysin that aid the bacteria during colonization, by facilitating adherence to the host,^[5] during invasion by damaging host cells,^[6] and during infection by interfering with the host immune response.^[7]

The lungs can normally filter out large droplets of aerosols. Smaller droplets 0.5 to 2 micrometer in size are deposited in the terminal alveoli and then engulfed by alevolar macrophages. These macrophages release cytokines and chemokines such as tumor necrosis factor-alpha, interleukin-8 and LTB4. This leads to accelerated recruitment of neutrophils to the involved area.^[8][1]

The ciliary lining of the respiratory epithelium serves to move secreted mucus containing trapped foreign particles, including pathogens, towards the oropharynx for either expectoration or swallowing. The elevated incidence of pneumonia among patients with genetic defects affecting mucociliary clearance, such as primary ciliary dyskinesia, suggests the important role of ciliary clearance in preventing community-acquired pneumonia.

Cough, together with mucociliary clearance, prevents pathogens from entering the lower respiratory tract. Cough suppression or cough reflex inhibition seen in patients with cerebrovascular accidents and drug overdoses is associated with an increased risk for aspiration pneumonia. The role of cough in preventing infection of the lower respiratory tract is demonstrated by a higher risk of pneumonia among patients with lower levels of bradykinin and tachykinins, such as substance P. These patients have a diminished cough reflex. ^[9][10]

Pathogen-associated molecular patterns (PAMPs) are initially recognized by Toll-like receptors (TLRs) and other pattern-recognition receptors (PRRs) of the innate immune system. Effectors in the acquired immune system are involved in elimination of microorganisms and generation of immunological memory. Other components of the immune system, such as complement system, cytokines, and collectins, also mediate the defense against microorganisms that cause pneumonia. Any defects in the this immune pathway can cause and increased risk of infections, namely pneumonia.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Chetan Lokhande, M.B.B.S [2]; Alejandro Lemor, M.D. [3]

Community-acquired pneumonia can be caused by viral, bacterial, and fungal organisms. Causative etiology varies with age, immune status, epidemiologic background, and comorbidity. The most common cause of CAP in adult outpatients and inpatients is Streptococcus pneumoniae. Patients admitted to the intensive care unit tend to have more aggressive organisms such as Staphylococcus aureus and Gram-negative bacilli. Neonates are most susceptible to Group-B-Streptococcus (GBS) which causes approximately 50% of pneumonias in the first week of life. Children and elderly patients are more susceptible to viral infections as well atypical bacterial pneumonias (Mycoplasma, Chlamydia, Legionella).

• Newborn infants, children, and adults are at risk for different spectrums of disease causing microorganisms.

• In addition, adults with chronic illnesses, who live in certain parts of the world, who reside in nursing homes, who have recently been treated with antibiotics, or who are alcoholics are at risk for unique infections.

• GBS causes at least 50% of cases of CAP in the first week of life.^[4]
• Other bacterial causes in the newborn period include Listeria monocytogenes and Mycobacterium tuberculosis.
• Viral causes like herpes simplex virus (most common), adenovirus, mumps, and enterovirus.

• For the most part, children older than one month are at risk for the same microorganisms as adults.
• Children less than five years are much less likely to have pneumonia caused by Mycoplasma pneumoniae, Chlamydophila pneumoniae, or Legionella pneumophila.^[4]
• In contrast, older children and teenagers are more likely to acquire Mycoplasma pneumoniae and Chlamydophila pneumoniae than adults.^[5]
• A unique cause of CAP in this group is Chlamydia trachomatis, which is acquired during birth but does not cause pneumonia until 2-4 weeks later.
• Common viruses include respiratory syncytial virus (RSV), metapneumovirus, adenovirus, parainfluenza, influenza, and rhinovirus.
• RSV in particular is a common source of illness and hospitalization.^[6]
• Fungi and parasites are not typically encountered in otherwise healthy infants, though maternally-derived syphilis can be a cause of CAP in this age group.

The causes of CAP in adults are outlined in the following categories.

• Viruses account for about 20% cases of CAP.
• Common viruses are influenza, parainfluenza, respiratory syncytial virus, metapneumovirus, and adenovirus.
• Less common viruses include chicken pox, SARS, avian flu, and hantavirus.^[7]

• Streptococcus pneumoniae is the most common cause of community-acquired pneumonia.
• Aspiration pneumonia is most commonly caused by anaerobic organisms.
• Prior to the development of antibiotics and vaccination, it was a leading cause of death.
• Traditionally, it was highly sensitive to penicillin, but during the 1970s resistance to multiple antibiotics began to develop.
• Current strains of drug resistant Streptococcus pneumoniae (DRSP) are common, accounting for twenty percent of all streptococcal infections.
• risk factors for DRSP in adults include: being older than 65, having exposure to children in day care, alcoholism, other severe underlying disease, or recent treatment with antibiotics; individuals exposed to these risk factors should initially be treated with antibiotics effective against DRSP.^[8]

• Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Legionella pneumophila are often grouped as atypical pneumonia. Community-acquired pneumonia caused by these agents present insidiously, with a non-productive cough and prominent extra-pulmonary complaints, such as myalgias and diarrhea (lack the typical pneumonia symptoms of fever, cough, and sputum).

• Mycoplasma pneumoniae is often referred to as “walking pneumonia.” It is transmitted via respiratory droplets and is common among healthy individuals in close contact with one another in settings such as dormitories or military barracks.

• Atypical organisms are more difficult to grow and respond to different antibiotics; they were discovered more recently than the typical bacteria discovered in the early twentieth century.

• Haemophilus influenzae used to be a common bacterial cause of CAP.
• First discovered in 1892, it was initially believed to be the cause of influenza because it commonly causes CAP in people who have suffered recent lung damage from viral pneumonia.

• Enteric bacteria such as Escherichia coli and Klebsiella pneumoniae may cause commnity-acquired penumonia.
• risk factors in adults for infection include: living in a nursing home, serious heart and lung disease, and recent antibiotic use; these individuals should initially be treated with antibiotics effective against enteric Gram-negative bacteria.

• Pseudomonas aeruginosa is an uncommon cause of CAP, but it is a particularly difficult bacteria to treat.
• Individuals who are malnourished, have bronchiectasis, are on corticosteroids, or have recently had strong antibiotics for a week or more, should initially be treated with antibiotics effective against Pseudomonas aeruginosa.^[9]

• Coccidioides spp. are common in southwestern area of the United States.
• Anaerobic infection is common in alcoholics. Pneumococcal pneumonia remains the most common cause of CAP in alcoholics.
• Psittacosis (caused by Chlamydophila psittaci) should be considered in the patient with exposure to birds or bird droppings.
• Anaerobes are common in patients with poor dental hygiene and a suspected large volume of aspiration.
• Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, and Legionella species are the common causes of community acquired pneumonia in those with chronic obstructive pulmonary disorders and smokers.
• Streptococcus pneumoniae, Gram-negative bacilli, Haemophilus influenzae, Staphylococcus aureus, anaerobes, and Chlamydophila pneumoniae are more common in nursing home residents.
• Streptococcus pneumoniae, Haemophilus influenzae, and Mycobacterium tuberculosis are common pathogens in early stages of HIV, whereas, Pneumocystis jiroveci, Histoplasma, and Cryptococcus are commonly seen in late stages HIV.
• In patients with structural lung disease such as bronchiectasis and cystic fibrosis, Pseudomonas aeruginosa, Burkholderia cepacia, and Staphylococcus aureus are the common pathogens involved.

• Incompetent swallowing mechanism, as can be found in neurological disease (a common cause being strokes) or while a person is intoxicated.
• Iatrogenic causes such as general anaesthesia for an operation. Patients are therefore instructed to be nil per os (NPO) for at least four hours before surgery.
• Whether aspiration pneumonia represents a true bacterial infection or a chemical inflammatory process remains the subject of significant controversy.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Pneumonia should be differentiated from other conditions that cause cough, fever, shortness of breath and tachypnea, such as asthma, COPD, CHF, cancer, GERD, and pulmonary emboli.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Chetan Lokhande, M.B.B.S [2]; Alejandro Lemor, M.D. [3]

Pneumonia is the ninth leading cause of death in the United States. It is the leading cause of death worldwide for children younger than 5 years of age. Both children and the elderly are at a higher risk for pneumonia complications. Countries in the Middle East and Africa have a higher pneumonia caused mortality rate amongst children.

• As many as 400,000 hospitalizations from pneumococcal pneumonia are estimated to occur annually in the United States. Pneumococci accounts for about 30% of adult community-acquired pneumonia. ^[2]

• In 2012, 59.9% of adults 65 years and older received a pneumococcal vaccination.^[3]

• In 2010, the number of discharges for patient admitted with pneumonia in hospitals in the US was 1.1 million patients. The average length of stay for pneumonia patients admitted to hospitals was 5.2 days.^[3]

• An increasing rate of CAP is seen with age. Approximately 5 to 6 cases of pneumonia per 1000 persons are observed among adults. A pronounced seasonal effect on the number of patients presenting to the emergency department is also noted. During the winter months, there is an approximately 50% rise in the number of cases compared to the summer months.^[4]

• Streptococcus pneumoniae is the leading cause of pneumonia worldwide.^[5]

• About 3.5 million deaths yearly have been attributed to lower respiratory tract infections (LRTI). LTRIs are the third most common cause of overall death and the leading cause of death from infectious diseases worldwide.^[6]
• Pneumonia is the ninth leading cause of death in the United States.
• The number of deaths in the US in 2011 attributed to pneumonia was 52,294. ^[3]
• Pneumonia mortality rate was 16.8 deaths per 100,000 in the US in 2011. ^[3]
• A higher mortality rate is seen in invasive diseases, nursing home patients and severe bacteremia.
• More than 40 % mortality rate is seen in ICU admitted patients.
• The percentage of hospital inpatient deaths from pneumonia in the US 2006 was 3.4%. ^[7]

• Individuals older than 85 years of age are at a particularly high risk of developing CAP that can reach an annual rate of 5-10%.^[8]

• Individuals younger than 3 years and older than 65 years of age are more likely to be hospitalized with severe symptoms and complications.

• The risk of CAP is similar in males and females.

▸ Click on the following regions to expand the data.

Editor(s)-in-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Priyamvada Singh, M.D. [2]; Philip Marcus, M.D., M.P.H.[3]; Chetan Lokhande, M.B.B.S [4]; Alejandro Lemor, M.D. [5]

The risk factors for pneumonia include: smoking, age, immunosuppression, exposure to chemicals, underlying lung disease, and exposure to chemicals.

• Airway obstruction may cause fluid accumulation in the lungs and result in CAP if the fluids become infected.

• One cause of obstruction, especially in young children, is inhalation of a foreign object such as a marble or toy. The object is lodged in the small airways and pneumonia can form in the trapped areas of lung.

• Another cause of obstruction is lung cancer, which can grow into the airways blocking the flow of air.

• Smoking, and diseases such as emphysema, result in more frequent and severe bouts of CAP.

• In children, recurrent episodes of CAP may be the first clue to diseases such as cystic fibrosis or pulmonary sequestration.

• Hypoxemia

• Pulmonary edema

• Chronic obstructive pulmonary disease (COPD)

• Previous episode of pneumonia or chronic bronchitis

• People who have immune disorders are more likely to acquire CAP.

• Risk factors for increased mortality from community-acquired pneumonia are: active malignancy, immunosuppression, neurological disease, congestive heart failure, coronary artery disease, and diabetes mellitus.

• People who have AIDS are much more likely to develop CAP. Pneumonia could be the first manifestation of an underlying undiagnosed HIV. It is, thus, recommended by the Center for Disease Control (CDC) that all patients aged 13 to 64 in a medical setting, regardless of known risk factors, be screened for HIV. The American College of Physicians and HIV Medicine Association recommends expanding screening for HIV from age 13 to 75 ^[2], ^[3].

• Other immune problems range from severe immune deficiencies from childhood, such as Wiskott-Aldrich syndrome, to less severe deficiencies, such as common variable immunodeficiency.^[6]

• Elderly people are affected with increased incidence and severity of community-acquired pneumonia. It is the fifth most common cause of death amongst individuals who are greater than 65 years of age, and it is the fourth most common cause of death in individuals who are 85 years or older. The clinical picture in elderly could be subtle and it could be present only as delirium without any fever, cough or sputum. Therefore, a high index of suspicion should be kept in these groups of people.

• Immotile cilia syndrome
• Kartagener’s syndrome (ciliary dysfunction, situs inversus, sinusitis, bronchiectasis)
• Young’s syndrome (azoospermia, sinusitis, pneumonia)

A few other conditions may lead to pneumonia due to altered pulmonary defense mechanisms.^[4]

• Dysphagia due to esophageal lesions and motility problems

• HIV infection (especially for pneumococcal pneumonia)

• Usage of H2 blockers, proton pump inhibitors, and antacids may increase the pH and, as a result, may increase the risk of pneumonia.^[5][6][7]

• A similiar study showed increase risk of pneumonia after starting PPI, especially within the first 48 hours.^[5][6][7] However, the association between PPI and CAP may be cofounded.^[8]

• A case control study has shown a significant correlation between the use of antipsychotic drugs and community-acquired pneumonia. A 60 percent increase in the rate of pneumonia can be seen in elderly patients who utilize antipsychotic medications.^[9]

• The use of atypical antipsychotics was associated with an increases risk of community-acquired pneumonia.

• A randomized trial has shown that ACE inhibitors reduce the risk of pneumonia.^[10]

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

There is insufficient evidence to recommend routine screening for community-acquired pneumonia

There is insufficient evidence to recommend routine screening for community-acquired pneumonia.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Chetan Lokhande, M.B.B.S [2]

Complications, including sepsis, respiratory failure, pleural effusion, and empyema, may occur despite appropriate antibiotic treatment. Complications are associated with bacterial pneumonia more frequently than they are with viral pneumonia. Most types of bacterial pneumonia can be cured within one to two weeks of appropriate medication. Viral pneumonia may last longer, and mycoplasmal pneumonia may take four to six weeks to resolve completely. The eventual outcome of an episode of pneumonia depends on how ill the person is when he or she is first diagnosed.

• Pneumococcal pneumonia is the most common clinical presentation of pneumococcal disease amongst adults, although pneumonia without bacteremia or empyema is not considered to be “invasive” disease. ^[1]
• The incubation period of pneumococcal pneumonia is short, about 1 to 3 days. ^[1]
• Symptoms generally include an abrupt onset of fever and chills or rigors. ^[1]
• Typically there is a single rigor; repeated shaking chills are uncommon. ^[1]
• Other common symptoms include: pleuritic chest pain, cough productive of mucopurulent, rusty sputum, dyspnea, tachypnea, hypoxia, tachycardia, malaise, and weakness. Nausea, vomiting, and headaches occur less frequently.^[1]
• Transmission of Streptococcus pneumoniae occurs as a result of direct person-to-person contact via respiratory droplets and by autoinoculation in persons carrying the bacteria in their upper respiratory tract. ^[1]
• The pneumococcal serotypes most often responsible for causing infection are those that are most frequently found in carriers.^[1]

• Community-acquired pneumonia may be complicated by parapneumonic pleural effusions. Thoracentesis and pleural fluid analysis should be performed.

• Empyema may occur if there is local formation of pus in the pleural cavity; this requires drainage in addition to antibiotic therapy.

• Intraparenchymal abscesses (with or without loculation) may be seen in aspiration pneumonia. They are often primarily anaerobic or polymicrobial.

• Sepsis most often occurs with bacterial pneumonia, with Streptococcus pneumoniae as the most common etiology.

• Patients at the opposite ends of the age spectrum are at a high risk of respiratory failure.

• Non-invasive maneuvers, such as a bilevel positive airway pressure (BI-PAP) machine, may be used for respiratory support. Otherwise, intubation with mechanical ventilation may be required.

• Pneumonia may be complicated by acute respiratory distress syndrome (ARDS), which results from a combination of infection and inflammatory response.

With treatment, most types of bacterial pneumonia can be cured within one to two weeks. Viral pneumonia may last longer, and mycoplasmal pneumonia may take four to six weeks to resolve completely. The eventual outcome of an episode of pneumonia depends on how ill the person is when he or she is first diagnosed.

In the United States, about one out of every twenty people with pneumococcal pneumonia will die.^[2] In cases where pneumonia progresses to blood poisoning (bacteremia), one of every five will die. The death rate (or mortality) also depends on the underlying cause of the pneumonia. Pneumonia caused by Mycoplasma, for instance, is associated with little mortality. However, about half of the people who develop methicillin-resistant Staphylococcus aureus (MRSA) pneumonia while on a ventilator will die.^[3] In regions of the world without advanced health care systems, pneumonia is even deadlier. Limited access to clinics and hospitals, x-rays, antibiotic choices, and inability to treat underlying conditions will inevitably lead to higher rates of death from pneumonia.

• Individuals who are treated for CAP outside of the hospital have a mortality rate of less than 1%.

• Fever typically responds in the first two days of therapy and other symptoms resolve in the first week.

• The CXR, however, may remain abnormal for at least a month, even when CAP has been successfully treated.

• Amongst individuals who require hospitalization, the mortality rate averages 12% overall, but it is as much as 40% in people who have bloodstream infections or require intensive care.^[3]

• When CAP does not respond as expected, there are several possible causes.

• A complication of CAP may have occurred or a previously unknown health problem may be playing a role.

• Additional causes include: inappropriate antibiotics for the causative organism (such as drug resistant Streptococcus pneumoniae, a previously unsuspected microorganism (such as tuberculosis), or a condition which mimics CAP (such as Wegener’s granulomatosis).

• Additional testing may be performed and may include radiologic imaging (such as a computed tomography scan) or a procedure such as a bronchoscopy or lung biopsy.

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