Community acquired pneumonia resident survival guide

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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]


A lower respiratory tract infection in a previously normal individual acquired through normal social contact rather than contracting it in a hospital. Community-acquired pneumonia (CAP) 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 dyspnea, fever, chest pain, and cough. CAP causes fluid accumulation in the alveoli leading to poor gas exchange. CAP is common worldwide and is a leading cause of illness and death. Causes of CAP include bacteria, viruses, fungi, and parasites. CAP can be diagnosed by history and a physical examination alone, though x-rays, sputum examinations, and other diagnostic tests are often used. As CAP is often bacterial, the primary empiric treatment consists of wide-spectrum antibiotics. Some forms of CAP, such as pneumococcal pneumonia may be prevented by vaccination.


Life Threatening Causes

Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated. Complications of community acquired pneumonia, such as pleural effusion, lung abscess, bacteremia and septicemia are life-threatening conditions and must be treated as such irrespective of the causes.

Common Causes

Following are the causes listed according to the microbiological etiology
  • Typical Bacteria
  1. Streptococcus pneumoniae
  2. Haemophilus influenzae
  3. Escherichia coli
  4. Klebsiella pneumoniae
  5. Pseudomonas aeruginosa
  • Atypical Bacteria
  1. Mycoplasma pneumoniae
  2. Chlamydophila pneumoniae
  3. Legionella pneumophila
  • Viruses
  1. Influenza
  2. Parainfluenza
  3. Respiratory syncytial virus (RSV)
  4. Metapneumovirus
  5. Adenovirus
Following are the causes listed according to the the location of the patient[1][2][3]
  • Outpatient
  1. Streptococcus pneumoniae
  2. Mycoplasma pneumoniae
  3. Haemophilus influenzae
  4. Chlamydophila pneumoniae
  5. Influenza A and B, adenovirus, respiratory syncytial virus, parainfluenza
  • Inpatient (non-ICU)
  1. Streptococcus pneumoniae
  2. Mycoplasma pneumoniae
  3. Chlamydophila pneumoniae
  4. Haemophilus influenzae
  5. Legionella
  6. Aspiration
  7. Influenza A and B, adenovirus, respiratory syncytial virus, parainfluenza
  8. Yersinia enterocolitica
  • Inpatient (ICU)
  1. Streptococcus pneumoniae
  2. Staphylococcus aureus
  3. Legionella
  4. Gram-negative bacilli
  5. Haemophilus influenzae
  6. Acinetobacter baumannii


Shown below is an algorithm depicting the management of community acquired pneumonia according to the Infectious Diseases Society of America (IDSA) and Thoracic Society Consensus Guidelines on the Management of Community Acquired Pneumonia in Adults.[4][5]

Characterize the symptoms:
Typical (acute onset)
Sputum production
Pleuritic chest pain
Confusion most prominently in the elderly
Shaking chills
Atypical (insidious onset)
❑ Dry cough
Sore throat
Examine the patient:

Vital signs

Fever is usually present in pneumonia
Hypothermia is one of the minor criteria of severity

Respiratory rate (tachypnea may be present)
Heart rate (tachycardia may be present)
Blood pressure (Hypotension requiring fluid rescusitation is one of the minor criteria of severity)
Pulse oximetry (Hypoxia might be present)

Respiratory examination:
❑ Decreased expansion of the thorax on inspiration on the affected side
Dull percussion on affected side
Bronchial breath sounds
RalesIncreased vocal fremitus
Pleural friction rub

Signs of increased severity:
❑ Persistent vomiting
❑ Fluctuating temperatures
Decreased level of consciousness

Look for signs suggestive of the infectious agent:
Abdominal pain, diarrhea, or confusion suggestive of Legionella
Rusty colored sputum suggestive of Streptococcus pneumoniae
Bloody sputum often described as "currant jelly" suggestive of pneumonia caused by Klebsiella
Hemoptysis suggestive of tuberculosis
Lymph node swelling and middle ear infection suggestive of Mycoplasma pneumonia

Inquire about history clues suggestive of the infectious agent:
❑ Recent travel
❑ Endemic exposure

Consider alternate diagnosis:
Acute bronchitis
Congestive heart failure
Chronic obstructive pulmonary disease
Gastroesophageal reflux disease
Upper respiratory tract infection
Bronchiolitis obliterans with organizing pneumonia
Pulmonary edema

Order laboratory tests:

Complete blood count (CBC)

Leukocytosis is usually present
Leukopenia (WBC <4000 cells/mm3) is one of the minor criteria of severity
Thrombocytopenia (platelets < 100,000 cells/mm3) is one of the minor criteria of severity

Blood urea nitrogen (BUN)

Uremia (BUN >20 mg/dL) is one of the minor criteria of severity


Elevated transaminases are suggestive of atypical pneumonia


Hyponatremia is suggestive of Legionella infection

Order imaging studies:
Chest X-ray PA and lateral

Consolidation (suggestive of typical pneumonia)
Patchy interstitial infiltrates (suggestive of atypical pneumonia)
Tap if pleural effusion > 5 cm
Does the patient have any of the following conditions that warranty additional testing?

❑ Admission to ICU due to severe pneumonia
❑ Failure of outpatient antibiotic therapy
❑ Cavitary infiltrates
Alcohol abuse
❑ Chronic severe liver disease
❑ Severe obstructive or structural lung disease
❑ Recent travel (within the last 2 weeks)
Pleural effusion
❑ Positive Legionella urine analysis test

❑ Positive pneumococcal urine analysis test
Additional lab tests are recommended
Additional lab tests are optional
Order additional testing:

❑ Blood gram stain and culture

Should be obtained before initiation of antibiotics

❑ Expectorated sputum gram stain and culture

Good sample should have <10 squamous cells/lpf, and >25 PMN/lpf if purulent sample
Sample should be transported to lab within 1-2 hours
Consider virus PCR or DFA for viruses

❑ Endotracheal aspirate gram stain and culture (if patient is intubated)
Arterial blood gas
❑ Urine legionella antigen
❑ Urine streptococcal antigen
Influenza testing during influenza season
Mycoplasma PCR for sputum or throat
Acid fast bacillus stain on induced sputum for tuberculosis
PCP in induced sputum if immunocompromised
❑ Consider HIV test among adults (15-60 years) if severe pneumonia
❑ Bronchoscopy if:

❑ Immunosuppression
❑ Failure to response
❑ Critical illness
❑ Chronic symptoms
❑ Suspected PCP but induced sputum test negative or inadequate
❑ Suspected tuberculosis but induced sputum is inadequate
Does the patient meet any of the following criteria for hospital admission?

CURB-65 score ≥ 2, OR

❑ High The Pneumonia severity index (PSI)
Treat as inpatient
Treat as outpatient
Does the patient have any of the following criteria for ICU admission?

❑ Invasive mechanical ventilation (major criteria), OR
❑ Septic shock with need for vasopressors (major criteria), OR
❑ At least 3 of the following minor criteria:

Respiratory rate >30 breaths/min
❑ PaO2/FiO2 ratio <250
❑ Multilobar infiltrates
Uremia (BUN >20 mg/dL)
Leukopenia (WBC <4000 cells/mm3)
Thrombocytopenia (platelets <100,000 cells/mm3)
Hypothermia (temperature <36 degrees C)
Hypotension that requires aggressive fluid resuscitation
Admit to ICU
Admit to general medical floor
❑ Begin empiric antibiotic treatment
❑ Follow up with cultures (if ordered) and change antibiotics according to the resistance profile
Does the patient have the following criteria of clinical stability?

Temperature ≤ 37.8 c
Respiratory rate ≤ 24 breaths/min
Heart rate ≤ 100 beats/min
Systolic blood pressure ≥ 90 mmHg
❑ Normal mental status
❑ Ability to tolerate oral intake

❑ Arterial oxygen saturation ≥ 90% or pO2 ≥ 60 mmHg on room air
Continue antibiotics
Consider alternative diagnoses
❑ Duration of treatment is not sufficient (< 72 hours)
Wait until > 72 hours and reassess

❑ The causative agent is not covered by antibiotics

Consider uncovered bacteria, and re-consider the antibiotics regimen

❑ The drug concentration is not sufficient (Vancomycin trough < 15 to 20 μg)

Check vancomycin trough concentration, and adjust the dose accordingly

❑ Resistant organism (MRSA or pseudomonas)

Consider bronchoscopy, and re-consider the antibiotics regimen

❑ Nosocomial superinfection

Consider bronchoscopy, and re-consider the antibiotics regimen

❑ Parapneumonic effusion

Order a chest X-ray, if negative consider CT scan
When effusion is present (especially if loculated), perform diagnostic tap and consider chest tube

❑ Parapneumonic empyema

Order a chest X-ray, if negative consider CT scan

❑ Alternate diagnoses (for example PE, fungal infection, viral pneumonia, chemical pneumonitis)

Consider CT scan

❑ Metastatic infection (endocarditis, arthritis, meningitis)

Order additional tests based on the suspicion

❑ Drug fever

Order a chest X-ray, if negative consider CT scan

❑ Exacerbation of an existing comorbidity

Order additional tests based on the suspicion

Empiric Antibiotics

Scenario Empiric Antibiotics
Previously healthy and no use of antimicrobials within the previous 3 months A macrolide
Presence of comorbidities such as chronic heart, lung, liver or renal disease; diabetes mellitus; alcoholism; malignancies; asplenia; immunosuppressing conditions or use of immunosuppressing drugs A fluoroquinolone (moxifloxacin, gemifloxacin, or levofloxacin [750 mg])

A b-lactam plus a macrolide

Use of antimicrobials within the last 3 months An alternative from a different class should be selected:

A fluoroquinolone (moxifloxacin, gemifloxacin, or levofloxacin [750 mg]) (strong recommendation; level I evidence)
A b-lactam plus a macrolide (strong recommendation; level I evidence)

In regions with a high rate (125%) of infection with high-level (MIC 16 mg/mL) macrolide-resistant Streptococcus pneumoniae A fluoroquinolone (moxifloxacin, gemifloxacin, or levofloxacin [750 mg])

A b-lactam plus a macrolide

General medical ward admission A respiratory fluoroquinolone
A b-lactam plus a macrolide
ICU admission A b-lactam (cefotaxime, ceftriaxone, or ampicillin-sulbactam) plus azithromycin
A b-lactam (cefotaxime, ceftriaxone, or ampicillin-sulbactam) plus a fluoroquinolone

For penicillin-allergic patients: a respiratory fluoroquinolone and aztreonam

Concern about pseudomonas An antipneumococcal, antipseudomonal b-lactam (piperacillintazobactam, cefepime, imipenem, or meropenem) plus either ciprofloxacin or levofloxacin (750 mg)

B-lactam plus an aminoglycoside and azithromycin
B-lactam plus an aminoglycoside and an antipneumococcal fluoroquinolone
For penicillin-allergic patients, substitute aztreonam for above b-lactam

Concern about community acquired MRSA Add vancomycin or linezolid

Empiric Antiviral

Scenario Empiric Antiviral
Symptoms suggestive of influenza and exposure to poultry in areas with previous H5N1 infection Test for H5N1
Initiate droplet precautions
Initiate routine infection control measures
Treat influenza with oseltamivir
Antibiotic coverage for S. pneumonia and S. aureus

Considerations in Severe Cases

Scenario Management
CAP + persistent septic shock Administer drotrecogin alpha
CAP + hypotension requiring resuscitation Screen for occult adrenal insufficiency
Hypoxemia Trial of noninvasive ventilation
Severe hypoxemia (PaO2/FiO2 < 150) + bilateral alveolar infiltrates Immediate intubation
ARDS or diffuse bilateral pneumonia on ventilation Low tidal volume ventilation (6 cm3/kg of ideal body weight)

Pneumonia Severity Index

Step 1

Does the patient have any of the following conditions?

Risk Class I
Step 2
Assess the following conditions and assign the corresponding scores:
Condition Points
If Male+Age (yrs)
If Female+Age (yrs) - 10
Nursing home resident +10
Neoplastic disease +30
Liver disease +20
Congestive heart failure +10
Cerebrovascular disease +10
Renal disease +10
Altered mental status+20
Pulse ≥125/minute +20
Respiratory rate >30/minute +20
Systolic blood pressure ≥90 mm Hg +15
Temperature <35°C or ≥40°C +10
Arterial pH <7.35 +30
Blood urea nitrogen ≥30 mg/dl (9 mmol/liter) +20
Sodium <90 mmol/liter +20
Glucose ≥250 mg/dl (14 mmol/liter)+10
Hematocrit <30%+10
Partial pressure of arterial O2 <60mmHg +10
Pleural effusion +10
∑ <70 = Risk Class II
∑ 71-90 = Risk Class III
∑ 91-130 = Risk Class IV
∑ >130 = Risk Class V


Criteria Score
Confusion (defined as an AMT of 8 or less) 1
Urea greater than 7 mmol/l (Blood Urea Nitrogen > 20) 1
Respiratory rate of 30 breaths per minute or greater 1
Blood pressure less than 90 systolic or diastolic blood pressure 60 or less 1
Age 65 or older 1


  • If the patient presented to the emergency department, administer the fist dose of antibitoic therapy as soon as possible, preferably within 6 hours of presentation.[6]
  • Among patients admitted to the hospital, switch from IV to PO antibiotics as soon as the patient is hemodynamically stable with clinical improvement and ability to tolerate oral intake. When the patient is switched to PO antibiotics, the patient can be discharged on PO home medications.
  • The duration of antibiotics is at least 5 days; antibiotic treatment are not discontinued until the patient is afebrile for 48-72 hours and with not more than one sign of instability.
  • Use fibre-optic bronchoscopy in immunocompromised individuals to detect less common organisms, obtain a tissue biopsy, and identify anatomic lesions if any.
  • Consider a F/U chest X-ray at 6 weeks to rule out an underlying lung malignancy.


  • Inadvertently use of antibiotic for patients without community-acquired pneumonia who require treatment within 4 hours may increase the risk of Clostridium difficile colitis.[7] Hence, use antibiotics judiciously.


  1. Mandell LA, Wunderink RG, Anzueto A, Bartlett JG, Campbell GD, Dean NC, Dowell SF, File TM, Musher DM, Niederman MS, Torres A, Whitney CG (2007). "Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults". Clinical Infectious Diseases : an Official Publication of the Infectious Diseases Society of America. 44 Suppl 2: S27–72. doi:10.1086/511159. PMID 17278083. Unknown parameter |month= ignored (help)
  2. Wong, KK.; Fistek, M.; Watkins, RR. (2013). "Community-acquired pneumonia caused by Yersinia enterocolitica in an immunocompetent patient". J Med Microbiol. 62 (Pt 4): 650–1. doi:10.1099/jmm.0.053488-0. PMID 23242642. Unknown parameter |month= ignored (help)
  3. Oh, YJ.; Song, SH.; Baik, SH.; Lee, HH.; Han, IM.; Oh, DH. (2013). "A case of fulminant community-acquired Acinetobacter baumannii pneumonia in Korea". Korean J Intern Med. 28 (4): 486–90. doi:10.3904/kjim.2013.28.4.486. PMID 23864808. Unknown parameter |month= ignored (help)
  4. "". Retrieved 13 March 2014. External link in |title= (help)
  5. "MMS: Error".
  6. Wilson, KC.; Schünemann, HJ. (2011). "An appraisal of the evidence underlying performance measures for community-acquired pneumonia". Am J Respir Crit Care Med. 183 (11): 1454–62. doi:10.1164/rccm.201009-1451PP. PMID 21239689. Unknown parameter |month= ignored (help)
  7. Meehan, TP.; Fine, MJ.; Krumholz, HM.; Scinto, JD.; Galusha, DH.; Mockalis, JT.; Weber, GF.; Petrillo, MK.; Houck, PM. (1997). "Quality of care, process, and outcomes in elderly patients with pneumonia". JAMA. 278 (23): 2080–4. PMID 9403422. Unknown parameter |month= ignored (help)

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