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
Pathophysiology
Epidemiology & Demographics
Risk Factors
Natural History, Complications & Prognosis
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
- Aerosol
- Aspiration of amniotic fluid
- Blood-borne infection across the
- Placenta
Newborn
- Commonest cause is Streptococcus agalactiae (Group B Streptococcus)
- 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 tuberculosis
- Viral causes like herpes simplex virus (commonest) adenovirus, mumps, and enterovirus
Children
- For the most part, children older than one month of life 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.[5]
- A unique cause of CAP in this group is Chlamydia trachomatis, which is acquired during birth but which 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.
Adults
Viruses
- Viruses cause 20% of CAP cases.
- Common viruses are influenza, parainfluenza, respiratory syncytial virus, metapneumovirus, and adenovirus.
- Less common viruses include chicken pox, SARS, avian flu, and hantavirus.[7]
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.[8]
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.[9]
Special situations
- Coccidioides are common in southwestern US.
- Anaerobic infection is common in alcoholics, nevertheless, pneumococcal pneumonia remains the most common cause of CAP in alcoholics too.
- Psittacosis (due to 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 suspected large volume of aspiration.
- Streptococcus pneumonia, H.influenza, Moraxella catarrhalis, and legionella species are the common causes of community acquired pneumonia in Chronic obstructive pulmonary disorders and Smokers.
- S. pneumonia, gram negative bacilli, H.influenza, staphylococcus aureus, anaerobes, and chlamydiae pneumonia are commoner in nursing home residents.
- S. pneumonia, H.influenza, and mycobacterium tuberculosis are common pathogens in early stages of HIV. Whereas, P.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 (pseudomonas), and staphylococcus aureus are the common pathogens involved.
Differentiating Pneumonia from other Diseases
- Acute bronchitis - No infiltrates on the CXR.
- Sinusitis - Sinus tenderness, post nasl drip.
- Asthma- No infiltrates on chest Xray.
- COPD - No infiltrates on chest Xray.
- Empyema - CXR showing features of pleural effusion, inflammatory markers on thoracocentesis.
- Pertussis - productive cough for weeks, nasopharyngeal aspirate aids in diagnosis.
- Lung abscess - CXR showing signs of lung abscess.
- Pulmonary embolus - A high degree of suspicion should be kept for pulmonary embolus. Chest X ray may be normal.
- Malignancy - CT scan and biopsy are helpful in ruling out malignancy.
- Vasculitis - Systemic manifestations of collagen vascular disease may be seen.
- Bronchiolitis obliterans with organizing pneumonia should be suspected in patients who don't respond to antibiotics treatment.
- Congestive heart failure - Bilateral pulmonary edema, involving more the lower lung fields.
- Gastroesophageal reflux disease - Normal chest Xray, symptoms worsening during night.
- Endocarditis with septic pulmonary emboli
- Upper respiratory tract infection
- Influenza
History and Symptoms
Common symptoms
- Dyspnea
- Productive cough (greenish or yellow sputum)
- Fever (high grade) with sweating, chills, and rigor
- Pleuritic chest pain
- Rapid, shallow breathing
Less common symptoms
Elderly
The manifestations of pneumonia, like those for many conditions, might not be typical in older people. They might instead experience:
- Delirium
- Hypothermia
- falls
Infant
Atypical pneumonia
Physical examination
The physical examination though not very sensitive and specific in diagnosis of community acquired pneumonia helps in determining the severity of illness and ruling out other differentials. Vital signs are useful in determining the severity of illness and have predictive values. However, high degree of suspicion should be kept in elderly as the presentation could be subtle in them.
Vital signs
- Fever
- Tachycardia > 125 beats/min
- Tachypnea
- Hypotension < 90 mm Hg
- Decreased oxygen saturation
Palpation
- Increased tactile fremitus
Percussion
- Dullness on percussion
Auscultation
- Decreased breath sounds
- Bronchial breath sounds
- Rhonchi
- Crackles, Rales
- Increased volume of whispered (vocal fremitus).[11]
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. Although there is no gold standard for the diagnosis of community acquired pneumonia (CAP), a new infiltrate on chest radiograph in the setting of acute respiratory complaints (e.g., cough and dyspnea) is considered highly suggestive of CAP.
- Atleast 2 of the four: fever, cough, dyspnea, chest pain
Lab diagnosis
Basic blood works
- Complete blood count (leucocytosis)
- Basic metabolic panel
Culture
- Sputum gram stain and culture have poor yield. Sputum culture provides 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
- Pulse oximeter - helps determine how well the lungs are able to work despite infection
- Arterial blood gas
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 treatment of pneumonia involves three critical decisions: firstly whether the patient truly has pneumonia, secondly what is the severity of the pneumonia, and lastly whether hospitalization is required for adequate management.
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[12]. 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:
- Respiratory rate > 30 breaths/minute;
- SBP < 90 mmHg;
- Heart rate > 125/min;
- Temperature < 35 or >40°C;
- 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.[13] 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.[14]
- 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[1] 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
- Smoking cessation is important not only for treatment of any underlying lung disease, but also because cigarette smoke interferes with many of the body's natural defenses against CAP.
- Vaccinations against Haemophilus influenzae and Streptococcus pneumoniae in the first year of life have greatly reduced their role in CAP in children.
- A vaccine against Streptococcus pneumoniae and influenza are also available for adults and is currently recommended for all healthy individuals older than 65 and any adults with emphysema, congestive heart failure, diabetes mellitus, cirrhosis, alcoholism, cerebrospinal fluid leaks, or who do not have a spleen.
- A repeat vaccination may also be required after five or ten years.[15]
- In addition, health care workers, nursing home residents, and pregnant women should receive the vaccine.[16]
- When an influenza outbreak is occurring, medications such as amantadine, rimantadine, zanamivir, and oseltamivir have been shown to prevent cases of influenza.[17]
References
- ↑ 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
- ^ Emedicine review of bacterial pneumonia
- ^ Metaly JP, Schulz R, Li Y-H, Singer DE, Marrie TJ, Coley CM, Hough LJ, Obrosky DS, Kapoor WN, Fine MJ. Influence of age on symptoms at presentation in patients with community-acquired pneumonia. Arch Intern Med 1997; 157: 1453-1459 PMID 9224224
- ^ Metlay, JP, Kapoor, WN, Fine, MJ. Does this patient have community-acquired pneumonia? Diagnosing pneumonia by history and physical examination. JAMA 1997; 278:1440. PMID 9356004
- ^ Syrjala H, Broas M, Suramo I, Ojala A, Lahde S. High resolution computed tomography for the diagnosis of community-acquired pneumonia. Clin Infect Dis 1998; 27: 358-363 PMID 9709887
- ^ Webber, S, Wilkinson, AR, Lindsell, D, et al. Neonatal pneumonia. Arch Dis Child 1990; 65:207.PMID 2107797
- ^ Abzug, MJ, Beam, AC, Gyorkos, EA, Levin, MJ. Viral pneumonia in the first month of life. Pediatr Infect Dis J 1990; 9:881. PMID 2177540
- ^ Wubbel, L, Muniz, L, Ahmed, A, et al. Etiology and treatment of community-acquired pneumonia in ambulatory children. Pediatr Infect Dis J 1999; 18:98. PMID 10048679
- ^ de Roux, A, Marcos, MA, Garcia, E, et al. Viral community-acquired pneumonia in nonimmunocompromised adults. Chest 2004; 125:1343.PMID 15078744
- ^ Ruhe, JJ, Myers, L, Mushatt, D, Hasbun, R. High-level penicillin-nonsusceptible Streptococcus pneumoniae bacteremia: identification of a low-risk subgroup. Clin Infect Dis 2004; 38:508 PMID 14765343
- ^ Lieberman D, Schlaeffer F, Boldur I, Lieberman D, Horowitz S, Friedman MG, Leiononen M, Horovitz O, Manor E, Porath A. Multiple pathogens in adult patients admitted with community-acquired pneumonia: a one year prospective study of 346 consecutive patients. Thorax 1996; 51: 179-184 PMID 8711652
- ^ Bradley, JS. Management of community-acquired pediatric pneumonia in an era of increasing antibiotic resistance and conjugate vaccines. Pediatr Infect Dis J 2002; 21:592. PMID 12182396
- ^ Niederman MS, Mandell LA, Anzueto A, Bass JB, Broughton WA, Campbell GD, Dean N, File T, Fine MJ, Gross PA, et al. Guidelines for the management of adults with community-acquired pneumonia: diagnosis, assessment of severity, antimicrobial therapy, and prevention. Am J Respir Crit Care Med 2001;163:1730–1754 PMID 11401897
- ^ Mundy, LM, Auwaerter, PG, Oldach, D, et al. Community-acquired pneumonia: impact of immune status. Am J Respir Crit Care Med 1995; 152:1309. PMID 7551387
- ^ Fine MJ, Auble TE, Yealy DM, Hanusa BH, Weissfeld LA, Singer DE, Coley CM, Marrie TJ, Kapoor WN. A prediction rule to identify low-risk patients with community-acquired pneumonia. N Engl J Med 1997; 336: 243-250 PMID 8995086
- ^ Woodhead MA, MacFarlane JT, McCracken JS, Rose DH, Finch RG. Prospective study of the aetiology and outcome of pneumonia in the community. Lancet 1987; i: 671-674. PMID 2882091
- ^ Garenne, M, Ronsmans, C, Campbell, H. The magnitude of mortality from acute respiratory infections in children under 5 years in developing countries. World Health Stat Q 1992; 45:180. PMID 1462653
- ^ Almirall, J, Bolibar, I, Balanzo, X, Gonzalez, CA. Risk factors for community-acquired pneumonia in adults: A population-based case-control study. Eur Respir J 1999; 13:349. PMID 10065680
- ^ Butler JC, Breiman RF, Campbell JF, Lipman HB, Broome CV, Facklam RR. Pneumococcal polysaccharide vaccine efficacy: an evaluation of current recommendations. JAMA 1993; 270: 1826-1831. PMID 8411526
- ^ Centers for Disease Control and Prevention. Prevention and control of influenza: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 1999;48(RR-4):1-28.
- ^ Hayden FG, Atmar RL, Schilling M, Johnson C, Poretz D, Paar D, Huson L, Ward P, Mills RG. Use of the selective oral neuraminidase inhibitor oseltamivir to prevent influenza. N Engl J Med 1999; 341: 1336-1343 PMID 10536125