Community-acquired pneumonia

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Editor-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]

Overview

Community-acquired pneumonia (CAP), also known as walking pneumonia, is a disease in which individuals who have not recently been hospitalized develop an infection of the lungs. CAP is a common illness and can affect people of all ages. It often causes problems like breathing, fever, chest pains, and a cough. CAP occurs when (alveoli) become filled with fluid and cannot work effectively. It occurs throughout the world and is a leading cause of illness and death. Causes of CAP include bacteria, viruses, fungi, and parasites. CAP can be diagnosed by symptoms and physical examination alone, though x-rays, examination of the sputum, and other tests are often used. CAP is primarily treated with antibiotic medication. Some forms of CAP can be prevented by vaccination.[4]

Pathophysiology

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

  • Viruses must invade cells in order to reproduce.
  • Typically, a virus will reach the lungs by traveling in droplets through the mouth and nose with inhalation.
  • There, the virus invades the cells lining the airways and the alveoli.
  • This invasion often leads cell death either through direct killing by the virus or by self-destruction through apoptosis.
  • Further damage to the lungs occurs when the immune system responds to the infection. White blood cells, in particular lymphocytes, are responsible for activating a variety of chemicals (cytokines) which cause leaking of fluid into the alveoli.
  • The combination of cellular destruction and fluid-filled alveoli interrupts the transportation of oxygen into the bloodstream.
  • In addition to the effects on the lungs, many viruses affect other organs and can lead to illness affecting 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

  • Bacteria and fungi also typically enter the lung with inhalation, though they can 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 also release cytokines which result in a general activation of the immune system.
  • This results in the fever, chills, and fatigue common in 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 lung into the blood stream and can result in serious illness such as septic shock, in which there is low blood pressure leading to damage in multiple parts of the body including the brain, kidney, and heart.

Parasites

  • In general, these parasites enter the body through the skin or by being swallowed.
  • 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.

Epidemiology and demographics

United states of America

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

International

  • It is a common illness in all parts of the world.

Age

  • It is a major cause of death among all age groups.
  • 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.[5]
  • Mortality decreases with age until late adulthood; elderly individuals are particularly at risk for CAP and associated mortality.

Seasonal

  • Common during winter months than during other times of the year.

Gender

  • CAP occurs more commonly in males than females

Race

  • More common in blacks than Caucasians.

Mortality

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

Special considerations

Risk factors

Some people have an underlying problem which increases their risk of getting an infection. Some important situations are covered below:

Obstruction

  • 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 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 block the flow of air.

Lung disease

Immune problems

  • 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 Centers for Disease Control (CDC) for HIV screening in all patients aged 13 to 64 in a medical setting regardless of known risk factors. The American College of Physicians and HIV Medicine Association recommends to broaden 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.[7]
  • Elderly are affected with increased incidence and severity of community acquired pneumonia. It is the fifth commonest cause of death among individuals who are > 65 years of age, and fourth in individuals who are 85years and more. 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 group of population.

Natural history, complications, and prognosis

Prognosis

  • Individuals who are treated for CAP outside of the hospital have a mortality rate less than 1%.
  • Fever typically responds in the first two days of therapy and other symptoms resolve in the first week.
  • The x-ray, however, may remain abnormal for at least a month, even when CAP has been successfully treated.
  • Among individuals who require hospitalization, the mortality rate averages 12% overall, but is as much as 40% in people who have bloodstream infections or require intensive care.[8]
  • 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 (ie DRSP), 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 additional radiologic imaging (such as a computed tomography scan) or a procedure such as a bronchoscopy or lung biopsy.

Complications

Despite appropriate antibiotic therapy, severe complications can result from CAP, including:

Sepsis

  • Sepsis can occur when microorganisms enter the blood stream and the immune system responds.
  • Sepsis most often occurs with bacterial pneumonia
  • Streptococcus pneumoniae is the most common cause.
  • Individuals with sepsis require hospitalization in an intensive care unit. They often require medications and intravenous fluids to keep their blood pressure from going too low. Sepsis can cause liver, kidney, and heart damage among other things.

Respiratory failure

  • If enough of the lung is involved, it may not be possible for a person to breathe enough to live without support.
  • Non-invasive machines such as a bilevel positive airway pressure machine may be used.
  • Otherwise, placement of a breathing tube into the mouth may be necessary and a ventilator may be used to help the person breathe.

Pleural effusion and empyema

  • Occasionally, microorganisms from the lung will cause fluid to form in the space surrounding the lung, called the pleural cavity.
  • If the microorganisms themselves are present, the fluid collection is often called an empyema.
  • If pleural fluid is present in a person with CAP, the fluid should be collected with a needle (thoracentesis) and examined.
  • Depending on the result of the examination, complete drainage of the fluid may be necessary, often with a chest tube. If the fluid is not drained, bacteria can continue to cause illness because antibiotics do not penetrate well into the pleural cavity.

Abscess

  • Rarely, microorganisms in the lung will form a pocket of fluid and bacteria called an abscess.
  • Abscesses can be seen on an x-ray as a cavity within the lung. Abscesses typically occur in aspiration pneumonia and most often contain a mixture of anaerobic bacteria.
  • Usually antibiotics are able to fully treat abscesses, but sometimes they must be drained by a surgeon or radiologist.

Causes

  • 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.

Infants

Source of infection

Newborn

Children

Adults

Viruses

Atypical organisms

  • 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 pneumonia is often called is "walking pneumonia." It is transmitted via respiratory droplets and is common among healthy individuals in close contact with one another, such as dormitories or military barracks.
  • Atypical organisms are more difficult to grow, respond to different antibiotics, and were discovered more recently than the typical bacteria discovered in the early twentieth century.

Streptococcus pneumoniae

  • Streptococcus pneumoniae is the commonest 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 highly sensitive to penicillin, during the 1970s resistance to multiple antibiotics began to develop.
  • Current strains of "drug resistant Streptococcus pneumoniae" or DRSP are common, accounting for twenty percent of all Streptococcus pneumoniae infections.
  • Adults with risk factors for DRSP including being older than 65, having exposure to children in day care, alcoholism other severe underlying disease, or recent treatment with antibiotics should initially be treated with antibiotics effective against DRSP.[13]

Hemophilus influenzae

  • Another 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 Gram negative bacteria

  • Involve colonic bacteria E.coli and K.pneumonia
  • Adults with risk factors for infection including residence in a nursing home, serious heart and lung disease, and recent antibiotic use should initially be treated with antibiotics effective against Enteric Gram negative bacteria.

Pseudomonas aeruginosa

  • Uncommon cause of CAP but 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.[14]

Special situations

History and Symptoms

Common symptoms

Less common symptoms

Elderly

The manifestations of pneumonia, like those for many conditions, might not be typical in older people. They might instead experience:

Infant

Atypical pneumonia

Physical examination

Vital signs

Palpation

  • Increased tactile fremitus

Percussion

  • Dullness on percussion

Auscultation

  • Decreased breath sounds
  • Crackles, Rales
  • Increased volume of whispered (vocal fremitus).[16]

Diagnosis

Diagnostic criteria for community acquired pneumonia

  • Patient who has not been hospitalized or in an institutional setting for the past 2 weeks and have the following findings:
    • CXR findings of a new infiltrate
    • Atleast 2 of the four: fever, cough, dyspnea, chest pain
Pneumonia. Chest x-ray showing increased shadowing in right lung (Right side of image). (Source: Center for Disease Control and Prevention.)

Lab diagnosis

Basic blood works

  • Complete blood count (leucocytosis)
  • Basic metabolic panel

Culture

  • Blood culture (definitive diagnosis with culture remains the gold standard)
  • Sputum gram stain and culture have poor yield, with sputum providing diagnostics information in roughly 1 in 5 patients only. (A good sputum sample contains small number of squamous epithelial cells and a large number of PMNs).
  • Blood cultures are not recommended for the outpatient management of CAP due to the low yield of pathogens.
  • Current guidelines recommend a combination of chest Xray,laboratory data as well as clinical judgment in diagnosis and management of community acquired pneumonia.

Oxygen monitoring

Imaging

  • X-rays of the chest (reveal areas of opacity). A normal chest x-ray makes CAP less likely; however, CAP is sometimes not seen on x-rays because the disease is either in its initial stages or involves a part of the lung not easily seen by x-ray.
  • Computed tomography in situations of diagnostic dilema.

Special tests

  • In more severe cases, (bronchoscopy) can be used collect fluid for culture.
  • Special tests can be performed if an uncommon microorganism is suspected (such as testing the urine for Legionella antigen when Legionnaires' disease is a concern).
  • HIV testing should be performed on all patients presenting with CAP (ages 13 to 75) in a medical setting.

Treatment

  • CAP is treated by administering an antibiotic which is effective in killing the offending microorganism as well as managing any complications of the infection.
  • If the causative microorganism is identified, different antibiotics are tested in the laboratory in order to identify which medication will be most effective.
  • Often, however, no microorganism is ever identified.
  • Also, since laboratory testing can take several days, there is some delay until an organism is identified.
  • In both cases, a person's risk factors for different organisms must be remembered when choosing the initial antibiotics (called empiric therapy).
  • Additional consideration must be given to the setting in which the individual will be treated.
  • Most people will be fully treated after taking oral pills while other people need to be hospitalized for intravenous antibiotics and, possibly, intensive care.
  • In general, all therapies in older children and adults will include treatment for atypical bacteria. Typically this is a macrolide antibiotic such as azithromycin or clarithromycin although a fluoroquinolone such as levofloxacin can substitute.

The decision to hospitalize

  • Some people with CAP require hospitalization and more intensive care than the majority. Clinical prediction rules, such as the pneumonia severity index and CURB-65 have been developed to help guide the decision[17]. Factors which increase the need for hospitalization include:
    • Age > 65 yrs, in most cases, men over 70 and women over 80 should be managed as inpatients when diagnosed with CAP
    • Confusion
    • Underlying chronic illnesses;
    • Evidence of infection outside the lung.
    • Vitals:
    • Laboratory results which increase the need for hospitalization include:
      • Arterial oxygen tension < 60 mm Hg,
      • Carbon dioxide > 50 mmHg,
      • pH < 7.35 on room air;
      • Hematocrit < 30%;
      • Creatinine > 1.2 mg/dl or
      • Blood urea nitrogen > 20 mg/ dl;
      • White blood cell count < 4 × 10^9/L or > 30 × 10^9/L; and
      • Absolute neutrophil count < 1 x 10^9/L.
      • X-ray findings which increase the need for hospitalization include involvement of more than one lobe of the lung, presence of a cavity, and the presence of a pleural effusion.

Newborn infants

Most newborn infants with CAP are hospitalized and given intravenous ampicillin and gentamicin for at least ten days. This treats the common bacteria Streptococcus agalactiae, Listeria monocytogenes, and Escherichia coli. If herpes simplex virus is the cause, intravenous acyclovir is administered for 21 days.

Children

Treatment of CAP in children depends on both the age of the child and the severity of his/her illness. Children less than five do not typically receive treatment to cover atypical bacteria. If a child does not need to be hospitalized, amoxicillin for seven days is a common treatment. However, with increasing prevalence of DRSP, other agents such as cefpodoxime will most likely become more popular in the future.[18] Hospitalized children should receive intravenous ampicillin, ceftriaxone, or cefotaxime.

Adults

In 2001, the American Thoracic Society, drawing on work by the British and Canadian Thoracic Societies, established guidelines for the management of adults with CAP which divided individuals with CAP into four categories based upon common organisms encountered.[19]

  • Healthy outpatients without risk factors
This group, the largest, is composed of otherwise healthy patients without risk factors for DRSP, enteric Gram negative bacteria, Pseudomonas, or other less common causes of CAP. The primary microoganisms in this group are viruses, atypical bacteria, penicillin sensitive Streptococcus pneumoniae, and Hemophilus influenzae. Recommended management is with a macrolide antibiotic such as azithromycin or clarithromycin for seven[3] to ten days.
  • Outpatients with underlying illness and/or risk factors
This group does not require hospitalization; its members either have underlying health problems (such as emphysema or congestive heart failure) or is at risk for DRSP and/or enteric Gram negative bacteria. Treatment is with a fluoroquinolone active against Streptococcus pneumoniae such as levofloxacin or a beta-lactam antibiotic such as cefpodoxime, cefuroxime, amoxicillin, or amoxicillin/clavulanate plus a macrolide antibiotic such as azithromycin or clarithromycin for seven to ten days.
  • Hospitalized individuals not at risk for Pseudomonas
This group requires hospitalization and administration of intravenous antibiotics. Treatment is with either an intravenous fluoroquinolone active against Streptococcus pneumoniae such as levofloxacin or beta-lactam antibiotic such as cefotaxime, ceftriaxone, ampicillin/sulbactam, or high-dose ampicillin plus an intravenous macrolide antibiotic such as azithromycin or clarithromycin for seven to ten days.
  • Individuals requiring intensive care at risk for Pseudomonas
Individuals being treated in an intensive care unit with risk factors for infection with Pseudomonas aeruginosa require specific antibiotics targeting this difficult to eradicate bacteria. One possible regimen is an intravenous antipseudomonal beta-lactam such as cefepime, imipenem, meropenem, or piperacillin/tazobactam plus an intravenous antipseudomonal fluoroquinolone such as levofloxacin. Another recommended regimen is an intravenous antipseudomonal beta-lactam such as cefepime, imipenem, meropenem, or piperacillin/ tazobactam plus an intravenous aminoglycoside such as gentamicin or tobramycin plus either an intravenous macrolide such azithromycin or an intravenous nonpseudomonal fluoroquinolone such as ciprofloxacin.

Prevention

References

  1. ↑ "Summaries for patients. Screening for HIV infection in health care settings: a guidance statement from the American College of Physicians and HIV Medicine Association". Annals of Internal Medicine. 150 (2): I–44. 2009. PMID 19047021. Retrieved 2012-09-04. Unknown parameter |month= ignored (help)
  2. ↑ Qaseem A, Snow V, Shekelle P, Hopkins R, Owens DK (2009). "Screening for HIV in health care settings: a guidance statement from the American College of Physicians and HIV Medicine Association". Annals of Internal Medicine. 150 (2): 125–31. PMID 19047022. Retrieved 2012-09-04. Unknown parameter |month= ignored (help)
  3. ↑ Li JZ, Winston LG, Moore DH, Bent S. Efficacy of short-course antibiotic regimens for community-acquired pneumonia: a meta-analysis. Am J Med. 2007 Sep;120(9):783-90. PMID 17765048
  1. ^ Emedicine review of bacterial pneumonia
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References

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