Pneumonia

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Hamid Qazi, MD, BSc [2], Serge Korjian M.D., Priyamvada Singh, M.D. [3]

The pneumonia syndrome has been recognized since ancient times. It was initially described by Hippocrates who recorded his observations of its symptoms and complications. Edwin Klebs was the first to identify bacteria in the lungs of patients who died from pneumonia in 1875. This discovery was soon-after substantiated by the works of Carl Friedländer and Albert Fränkel who were the first to identify Streptococcus pneumoniae as a causative agent. The introduction of the gram stain subsequently led to the discovery of other causative organisms. Despite being an important cause of mortality before the late twentieth century, the advent of antibiotics, modern surgical techniques, and vaccination drastically lowered the morbidity and mortality of pneumonia with the turn of the century.

• Pneumonia was first discovered by Hippocrates.
• In 1817, Dr. Simpson of United Kingdom was the first to report a case of pneumonia treated with blood letting.^[1]
• In 1842, Dr. Edward Newfold of United Kingdom was the first to report a case of typhoid pneumonia.^[2]
• In 1875, Dr. Edwin Klebs was the first to discover the association between bacteria and the development of pneumonia.

• In 1902, Dr. Wright discovered the pneumococcal vaccine as a preventative treatment of pneumonia.^[3]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Hamid Qazi, MD, BSc [2], Priyamvada Singh, M.D. [3]

Bacteria and fungi typically enter the lung with inhalation. Once inside the alveoli, these microbes travel into the spaces between the cells and also between adjacent alveoli through connecting pores. This invasion triggers the immune system response by sending white blood cells responsible for attacking microorganisms (neutrophils) to the lungs resulting in manifestations of pneumonia.

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

• Aspiration of oropharyngeal contents containing pathogenic microorganisms is one of the mechanism of acquiring pneumonia.
• It most commonly occurs in normal persons during sleep, in unconscious persons due to gastroesopahegeal reflux or impaired gag reflex and cough reflex.^[1]

• Microbial entered through circulation may also result in pulmonary infections.
• Blood-borne pneumonia is seen more commonly in intravenous drug users. Staphylococcus aureus causes pneumonia in this way.
• 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 strategies are evolved to evade host defence mechanisms and facilitate spreading before establishing an infection.

• Influenza virus possesses neuraminidases for cleavage of sialic acid residues on the cell surface and viral proteins, which prevent aggregation and facilitate propagation of viral particles.

• Chlamydophila pneumoniae induces complete abortion of cilia motions which assists colonization at the respiratory epithelium.^[2]

• Mycoplasma pneumoniae produces a virulence factor with ADP-ribosylating activity which is responsible for airway cellular damage and mucociliary dysfunction.^[3]

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

• Streptococcus pneumoniae possesses pneumolysin that aid the bacteria during colonization, by facilitating adherence to the host,^[4] during invasion by damaging host cells,^[5] and during infection by interfering with the host immune response.^[6]

• The lungs can normally filter out large droplets of aerosols.
• Smaller droplets of the size of 0.5 to 2 micrometer are deposited on the alveoli and then engulfed by alevolar macrophages.
• These macrophages release cytokines and chemokines, which also includes tumor necrosis factor-alpha, interleukin-8 and LTB4.
• The neutrophils are recruited by these cells to eliminate these microorganisms.^[7][8]

• The cilia lining the respiratory epithelium serve to move secreted mucus containing trapped foreign particles including pathogens towards the oropharynx for either expectoration or swallowing.
• Elevated incidence of pneumonia in patients with genetic defects affecting mucociliary clearance such as primary ciliary dyskinesia suggests its role in the pathogenesis of community-acquired pneumonia.

• Cough, together with mucociliary clearance, prevent pathogens from entering the lower respiratory tract.
• Cough suppression or cough reflex inhibition seen in patients with cerebrovascular accidents and drug overdosages is associated with an enhanced risk for aspiration pneumonia.
• Another relation to cough is genetic polymorphisms in the angiotensin-converting enzyme (ACE) gene.
• The role of cough in preventing pneumonia may be explained by a higher risk for developing pneumonia in homozygotes carrying deletion/deletion (DD) genotype who are found to have lower levels of bradykinin and tachykinins such as substance P.^[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 in the immune system such as complement system, cytokines, and collectins, also mediate the defense against microorganisms causing pneumonia.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Hamid Qazi, MD, BSc [2], Priyamvada Singh, M.D. [3]; Alejandro Lemor, M.D. [4]; Ogheneochuko Ajari, MB.BS, MS [5]

Pneumonia can result from a variety of causes, including infection with bacteria, viruses, fungi, parasites, and chemical or physical injury to the lungs. The etiology will depend upon various factors such as age, immune status, geographical area, and comorbidities.

Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated.

• Anthrax

• Cryptococcus neoformans
• Flu
• Histoplasmosis
• Hospital-acquired pneumonia
• Mycoplasma pneumonia
• Pneumocystis jiroveci
• Respiratory syncytial virus
• Rhinovirus
• Streptococcus pneumoniae

Click here for bacterial pneumonia

Click here for viral pneumonia

Click here for fungal pneumonia

• Aerosol
• Aspiration of amniotic fluid
• Blood-borne infection across the placenta

• Most common cause is Streptococcus agalactiae (Group B Streptococcus)
• GBS causes at least 50% of cases of CAP in the first week of life.^[1]
• Other bacterial causes in the newborn period include Listeria monocytogenes and 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.
• However, children less than five years are much less likely to have pneumonia caused by mycoplasma pneumoniae, chlamydophila pneumoniae, or legionella pneumophila.
• In contrast, older children and teenagers are more likely to acquire mycoplasma pneumoniae and chlamydophila pneumoniae than adults.^[2]
• 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.^[3]
• 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.

• 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.^[6]
• 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.^[7]
• In contrast, older children and teenagers are more likely to acquire Mycoplasma pneumoniae and Chlamydophila pneumoniae than adults.^[7]
• 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.^[8]
• 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.^[9]

• 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.^[10]

• 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.^[11]

• 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.

The causes of hospital acquired pneumonia are as follows:^[8]

• Commonly polymicrobial
• Common microbial agents include:
  • Pseudomonas aeruginosa
  • Escherichia coli
  • Klebsiella pneumoniae
  • Acinetobacter

• Staphylococcus aureus
• Methicillin resistant staphylococcus aureus (common in patients with diabetes mellitus, head trauma, and in ICU)

• S. aureus
• Enteric gram-negative rods
• Streptococcus pneumoniae
• Pseudomonas

• The microbiologic flora responsible for VAP is different from that of the more common community-acquired pneumonia (CAP). In particular, viruses and fungi are uncommon causes in people who do not have underlying immune deficiencies.
• Though any microorganism that causes CAP can cause VAP, there are several bacteria which are particularly important causes of VAP because of their resistance to commonly used antibiotics. These bacteria are referred to as multidrug resistant (MDR).
• VAP has been classified into either early-onset pneumonia (EOP), if pneumonia develops within 96 hours of the patient’s admission to an ICU or intubation for mechanical ventilation, and late-onset pneumonia (LOP), if pneumonia develops after 96 hours of the patient’s admission to an ICU or intubation for mechanical ventilation. ^[9]
• This categorization can be helpful to clinicians in initiating empiric antimicrobial therapy for cases of pneumonia, when the results of microbiologic diagnostic testing are not yet available.
• EOP has been associated usually with non-multi-antimicrobial-resistant microorganisms such as Escherichia coli, Klebsiella spp., Proteus spp., S. pneumoniae, H. influenzae, and oxacillin-sensitive S. aureus.
• On the other hand, LOP has been associated with Pseudomonas aeruginosa, oxacillin-resistant S. aureus, and Acinetobacter spp (strains that are usually multi-antibiotic-resistant).

The following is a list of the most MDR common pathogens associated with ventilator-associated pneumonia:

• Pseudomonas aeruginosa is the most common MDR gram-negative bacterium causing VAP. Pseudomonas has natural resistance to many antibiotics and has been known to acquire resistance to every antibiotic except for polymixin B. Resistance is typically acquired through upregulation or mutation of a variety of efflux pumps which pump antbiotics out of the cell. Resistance may also occur through loss of an outer membrane porin channel (OprD).
• Klebsiella pneumoniae has natural resistance to some beta-lactam antibiotics such as ampicillin. Resistance to cephalosporins and aztreonam may arise through induction of a plasmid-based extended spectrum beta-lactamase (ESBL) or plasmid-based ampC-type enzyme.
• Serratia marcescens has an ampC gene which can be induced by exposure to antibiotics such as cephalosporins. Thus, culture sensitivities may initially indicate appropriate treatment which fails due to bacterial response.
• Enterobacter as a group also have an inducible ampC gene. Enterobacter may also develop resistance by acquiring plasmids.
• Citrobacter also has an inducible ampC gene.
• Stenotrophomonas maltophilia often colonizes people who have endotracheal tubes or tracheostomies but can also cause pneumonia. It is often resistant to a wide array of antibiotics but is usually sensitive to co-trimoxazole.
• Acinetobacter are becoming more common and may be resistant to carbapenems such as imipenem and meropenem.
• Burkholderia cepacia is an important organism in people with cystic fibrosis and is often resistant to multiple antibiotics.
• Methicillin-resistant Staphylococcus aureus is an increasing cause of VAP. As many as fifty percent of Staphylococcus aureus isolates in the intensive care setting are resistant to methicillin. Resistance is conferred by the mecA gene.

• Incompetent swallowing mechanism, such as 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.

• Blinatumomab
• Belimumab
• Boceprevir
• Ceritinib
• Dornase Alfa
• Enfuvirtide
• ethanolamine oleate
• Felbamate
• Iloperidone
• interferon alfacon-1
• Pegylated interferon alfa-2b

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Hamid Qazi, MD, BSc [2], Priyamvada Singh, M.D. [3] Syed Hassan A. Kazmi BSc, MD [4]

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

Table 1: Differentiating psittacosis from other diseases

Key;

+, occurs in some cases

++, occurs in many cases,

+++, occurs frequently

Pnemonia must be differentiated from other diseases that cause atypical pneumonia such as Q fever and legionella pneumonia:

Disease	Prominent clinical features	Lab findings	Chest X-ray
Q fever	Q fever is characterized by abrupt onset of fever, myalgia, headache, and other constitutional symptoms. Cough is the most prominent respiratory symptom and it is usually dry.[17] Cough is associated with dyspnea and pleuritic chest pain.	Antibody detection using indirect immunofluorescence (IIF) is the preferred method for diagnosis. PCR can be used if IIF is negative, or very early once disease is suspected. C. burnetii does not grow on ordinary blood cultures, but can be cultivated on special media such as embryonated eggs or cell culture. A two-to-three fold increase in AST and ALT is seen in most patients.
Mycoplasma pneumonia	Mycoplasma pneumonia can be asymptomatic. Headache, nausea, and malaise usually precede the onset of symptoms.[17] Cough is intractable and nonproductive.	Postitve Coombs test Leukocytosis Thrombocytosis
Legionellosis	Legionellosis is characterized by cough that is slightly productive.[17] Constitutional symptoms such as chills, myalgia, and arthralgia. Gastrointestinal symptoms such as diarrhea, nausea, and vomiting.	Labs are nonspecific for diagnosing legionellosis Renal and hepatic dysfunction Thrombocytopenia and leukocytosis Hyponatremia
Chlamydia pneumonia	There are no specific clinical features of chlamydia pneumonia. Symptoms appear gradually. Chlamydia infection is usually associated with upper respiratory tract symptoms (pharyngitis, sinusitis, etc). It might be associated with extrapulmonary maifestations such as meningitis and Guillain-Barre syndrome.[17]	Chlamydia pneumonia is usually associated with normal WBC count. Diagnosed with the presence of antichlamydial antibody (through complement fixation or direct immunofluoroscence) or direct antigen detection.

Pneumonia should be differentiated from other diseases presenting with cough, fever, shortness of breath and tachypnea. The differentials include the following:^{[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]}

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Hamid Qazi, MD, BSc [2], Priyamvada Singh, M.D. [3]; Alejandro Lemor, M.D. [4]

Pneumonia is a common illness in all parts of the world. It is a major cause of death among all age groups. Mortality from pneumonia generally decreases with age until late adulthood. Elderly individuals, however, are at particular risk for pneumonia and associated mortality. More cases of pneumonia occur during the winter months than during other times of the year. Pneumonia occurs more commonly in males than females, and more often in African Americans than caucasians. People who are hospitalized for any reason are also at high risk for pneumonia. Following urinary tract infections, pneumonia is the second most common cause of nosocomial infections, and its prevalence is 15-20% of the total number.

Table 1. Incidence of pneumococcal infections in the United States. Age (years) Disease Incidence Cases/100,000 (number of cases) Death Rate Deaths/100,000 (number of deaths) <1 31.4 (142) 0.22 (1) 1 24.6 (112) 0.22 (1) 2-4 12.6 (171) 0.15 (2) 5-17 2.2. (111) 0.02 (1) 18-34 3.7 (261) 0.26 (18) 35-49 10.3 (670) 0.65 (42) 50-64 19.5 (1,068) 1.86 (102) ≥ 65 37.0 (1,291) 5.61 (196) Total 12.9 (3,828) 1.22 (363) Adapted from CDC[5]

• It is the seventh most common cause of death in the United States
• It causes around 500,000 hospitalizations and 65,000 deaths annually.

• It is a common illness in all parts of the world, but countries like India, China, Pakistan, Bangladesh, Indonesia and Nigeria have high rates of childhood pneumonia.^[2]

• The incidence is higher in children and elderly.
• In children, the majority of deaths occur in the newborn period, with over two million worldwide deaths a year.
• In fact, the WHO estimates that one in three newborn infant deaths are due to pneumonia.
• Mortality decreases with age until late adulthood; elderly individuals are particularly at risk for CAP and associated mortality.

• More common during winter months than during other times of the year.

• CAP occurs more commonly in males than females

• More common in African Americans than caucasians.

• Patients hospitalized with pneumonia have a mortality rate of 12-14%.

• Individuals with underlying illnesses such as Alzheimer’s disease, cystic fibrosis, emphysema, tobacco smoking, alcoholism, or immune system problems are at increased risk for pneumonia.^[6]

• 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. ^[5]

• In 2012, 59.9% of adults 65 years and older received a pneumococcal vaccination.^[6]

• 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.^[6]

• 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.^[7]

• Streptococcus pneumoniae is the leading cause of pneumonia worldwide.^[8]

• 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.^[9]
• 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. ^[6]
• Pneumonia mortality rate was 16.8 deaths per 100,000 in the US in 2011. ^[6]
• 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%. ^[10]

• 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%.^[11]

• 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.

• Pneumonia has accounted for approximately 20% of all hospital-associated infections and 27% and 24% of all infections acquired in the medical intensive-care unit (ICU) and coronary care unit, respectively. ^[13]

• The incidence of HAP is 5-15 cases per 1 000 hospital admissions. ^[14]
• The incidence of VAP is 6 to 20 times more than in patients without mechanical support.

• HAP and VAP are nosocomial infections with a high mortality in contrast with other nosocomial infections.
• This higher mortality rate is associated with MDR pathogens.

• HAP is more commonly reported in patients > 65 years, probably due to the fact that this age population is more commonly hospitalized.

• There is no predominance in gender, although some data reports a higher incidence among females.

• VAP occurs in up to 25% of all people who require mechanical ventilation.
• VAP can develop at any time during ventilation, but occurs more often in the first few days after intubation.
• This is because the intubation process itself contributes to the development of VAP.
• VAP occurring early after intubation typically involves fewer resistant organisms and is thus associated with a more favorable outcome.
• Because respiratory failure requiring mechanical ventilation is itself associated with a high mortality, determination of the exact contribution of VAP to mortality has been difficult.
• As of 2006, estimates range from 33% to 50% death in patients who develop VAP.
• Mortality is more likely when VAP is associated with certain microorganisms (Pseudomonas, Acinetobacter), blood stream infections, and ineffective initial antibiotics.
• VAP is especially common in people who have acute respiratory distress syndrome (ARDS).

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Hamid Qazi, MD, BSc [2], Priyamvada Singh, M.D. [3]Philip Marcus, M.D., M.P.H.[4]

The risk factors for pneumonia include: smoking, age>65, immuno-suppression, exposure to chemicals, and underlying lung disease.

• When part of the airway (bronchi) leading to the alveoli is obstructed, the lung is not able to clear fluid when it accumulates. This can lead to infection of the fluid resulting in community-acquired pneumonia (CAP).
• 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.

• People who have immune system problems are more likely to get CAP.
• Risk factors for increased mortality from community acquired pneumonia are: active malignancy, immuno-suppression, 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 ^[1], ^[2].
• Other immune problems range from severe immune deficiencies of childhood such as Wiskott-Aldrich syndrome to less severe deficiencies such as common variable immunodeficiency.^[5]
• Elderly people are affected with increased incidence and severity of community acquired pneumonia. It is the fifth most common cause of death among individuals who are > 65 years of age, and fourth in individuals who are 85 years or older. The clinical picture in elderly could be subtle and could present only as delirium without any fever, cough or sputum. Therefore, a high index of suspicion should be kept in these groups of people.

The following are risk factors related to specific causative pathogens in community-acquired pneumonia:

• 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 ^[1], ^[2].

• 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)