Community-Acquired Pneumonia Case File

Community-Acquired Pneumonia Case File

Eugene C. Toy, MD, Gabriel M. Aisenberg, MD

Case 19

A 44-year-old man presents to the emergency department with sudden onset of shaking chills, fever, and productive cough. He was in his usual state of good health until 1 week ago, when he developed mild nasal congestion and generalized achiness. Last night he became feverish and fatigued, and he developed a cough associated with nonbloody sputum production and right-sided chest pain. The patient also expressed mild exertional dyspnea when walking his dog this morning. His medical history is remarkable only for mild, intermittent asthma, hypertension, and hyperlipidemia. His medications are lisinopril and atorvastatin. The patient admits to smoking a pack per day for the last 20 years. He states he drinks a glass of wine two or three times a week and denies drug use. In your office, his vital signs are normal except for a temperature of 39 °C (102.2 °F). His oxygen saturation is 100% on room air. Physical examination shows a mostly comfortable man (except when he coughs) with bronchial breath sounds and end-inspiratory crackles in the right lower lung field. The remaining examination is unremarkable. A chest x-ray demonstrates a homogeneous opacity with bronchogram on the right lower pulmonary field.

▶ What is the most likely diagnosis?

▶ What is the most likely etiology of this disease process?

▶ What is your next step?

▶ What are risk factors for this condition?

ANSWERS TO CASE :

Community-Acquired Pneumonia

Summary: A 44-year-old man presents with

• Sudden onset of shaking chills, fever, dyspnea on exertion, and productive cough with pleuritic chest pain
• A 102.2 °F fever without tachypnea or hypoxia
• Bronchial breath sounds and end-inspiratory crackles in the right lower lung field
• Consolidation on the right pulmonary base on chest x-ray

Most likely diagnosis: Community-acquired pneumonia (CAP).

Most likely etiology: The etiologies of CAP within this patient’s demographic include Haemophilus influenzae, Staphylococcus aureus, group A streptococci, Moraxella catarrhalis, viruses, Mycoplasma pneumoniae, Chlamydia pneumoniae, Chlamydia psittaci, and Legionella species; however, the most common isolate is Streptococcus pneumoniae.

Next step: Chest x-ray. If the images confirm the suspicion of pneumonia, then start antibiotic therapy, pain relievers, antipyretics, and cough suppressants for relief of symptoms. Close outpatient follow-up (in 1-2 weeks) is also important.

Risk factors: Common CAP risk factors include alcohol abuse, smoking, Chronic obstructive pulmonary disease (COPD), immunosuppression, and recent influenza infection.

ANALYSIS

Objectives

1. Identify the causative organisms in CAP and the appropriate therapeutic regimens. (EPA 3, 4)
2. Differentiate the clinical criteria indicating inpatient versus outpatient therapy. (EPA 4, 7, 10)
3. Analyze the role of radiologic and laboratory evaluation in the diagnosis of pneumonia. (EPA 3)
4. Compare and contrast the difference between chemical pneumonitis and infectious aspiration pneumonia. (EPA 1, 2)

Considerations

This previously healthy 44-year-old man displayed clinical and radiographic evidence of a focal lung consolidation, which is consistent with a bacterial process, such as a S. pneumoniae infection. The specific causative organism is usually not definitively established, so empiric antimicrobial therapy will need to be initiated and the patient response monitored. It will also be necessary to risk stratify the patient to determine whether he can safely be treated as an outpatient or requires hospitalization.

APPROACH TO:

Community-Acquired Pneumonia

DEFINITIONS

COMMUNITY-ACQUIRED PNEUMONIA (CAP): An infection of the alveoli, distal airways, and interstitium of the lungs that is acquired outside the hospital setting, affecting individuals of all ages.

HEALTH CARE–ASSOCIATED PNEUMONIA (HCAP): Pneumonia developing 48 hours after admission that was not present prior to admission. The previous concept of HCAP has since fallen out of favor due to its inability to be sensitive or specific in identifying patients who might be at risk. HCAP was previously defined as pneumonia occurring in a nonhospitalized patient with extensive health care contact, including one of the following: intravenous therapy, wound care, intravenous chemotherapy within the prior 30 days, those who live in a nursing home or other long-term care facility, hospitalization in an acute care hospital for 2 or more days within the prior 90 days, or attendance at a hospital or hemodialysis clinic within the prior 30 days. Recently, terminology has changed so that nursing home patients who develop pneumonia is called CAP.

PNEUMONIA: Inflammation of the lung parenchyma, which may be caused by bacteria, viruses, fungi, or rarely protozoa or noninfectious diseases. In the day-to-day medical language, it refers to an infection affecting the lung.

VENTILATOR-ASSOCIATED PNEUMONIA: Pneumonia that develops 48 hours after intubation.

CLINICAL APPROACH

Pathophysiology

Community-acquired pneumonia, as opposed to HCAP, in adults is most commonly caused by S. pneumoniae, M. pneumoniae, H. influenzae, C. pneumoniae, or respiratory viruses, such as influenza and adenovirus. Despite a careful history and physical, routine laboratory tests, and radiographic investigation, it remains difficult to determine a specific pathogen in most cases. Epidemiologic risk factors and certain exposures may provide additional clues: C. psittaci is associated with bird exposure, coccidioidomycosis is associated with travel to the American southwest, and histoplasmosis is endemic to the Mississippi Valley and common in spelunkers. In a patient with acquired immunodeficiency syndrome (AIDS) or immunosuppression, Pneumocystis jiroveci should instantly be added to the differential diagnosis. Tuberculosis should always be considered a possibility in patients with a history suggestive of exposure or predisposition (ie, homelessness or exposure to shelters, previous incarceration, emigration from countries of high endemicity, unvaccinated or immunocompromised state) to this disease.

Pathogens in HCAP include methicillin-resistant S. aureus (MRSA), Pseudomonas aeruginosa, Acinetobacter spp, and multidrug-resistant Enterobacteriaceae. Empiric antibiotic therapy should be directed accordingly.

Clinical Presentation

Pneumonia represents inflammation, commonly infectious of the lung parenchyma. Patients may present with any combination of cough, fever, pleuritic chest pain, sputum production, shortness of breath, hypoxia, and respiratory distress. Certain clinical presentations are associated with particular infectious agents. For example, characteristics of “typical” pneumonia include sudden onset of fever, cough with productive sputum, pleuritic chest pain, and occasionally rust-colored sputum. This describes the classic presentation of pneumococcal pneumonia.

The “atypical” pneumonia is recognized by a more insidious onset, a dry cough, and prominent extrapulmonary symptoms such as headache, myalgias, and sore throat. In addition, a chest radiograph usually appears much worse than the clinical or auscultatory findings. M. pneumoniae remains the most commonly identified pathogen attributed to “atypical” pneumonia. Although these characterizations are of some diagnostic value, there are no features that can distinguish between typical and atypical pneumonia based on the clinical history and physical examination alone. Therefore, pneumonias are typically classified according to the immune status of the host, the radiographic findings, and the setting in which the infection was acquired in an attempt to identify the most likely causative organisms and to guide initial empiric therapy.

Risk Stratification. Once the clinical diagnosis of infectious pneumonia has been made, the next step is to risk stratify the patients to determine which patients can be treated safely as outpatients with oral antibiotics and which require hospitalization. Two major risk stratification tools are currently employeds: the Pneumonia Severity Index (PSI) and the CURB-65. The PSI stratifies patients into five groups based on a 30-day all-cause mortality in those with radiographically proven pneumonia. This two-step processes involves first using patient demographic factors:— age > 50, medical history comorbidities, and physical examination findings—to determine low-risk patients (risk class I: outpatient treatment). Patients possessing these factors progress to step 2, which utilizes objective laboratory findings to further classify patients in classes II to IV based on the number of points assigned per risk factor. Scoring is determined by taking the age (subtract 10 in women) and adding a point for each risk factor. The other stages are as follows: class II (scores < 70), class III (score 71-90), class IV (scores 91-130), and class V (scores > 130). Patients in classes I and II have a predicted mortality of less than 0.6% and are suitable for outpatient treatment, while patients in class V have a 30-day mortality risk of 27%. Calculating PSI is laborious.

The CURB-65 serves as a simplified prognostic score using five variables:

Confusion (1 point)

Urea greater than 20 mg/dL (1 point)

Respiratory rate greater than 30 breaths/min (1 point)

Blood pressure, systolic less than 90 mm Hg (1 point)

Age greater than 65 (1 point)

Patients with a score of 0 to 1 have a 30-day mortality below 3%, and they can usually be safely treated as outpatients with oral antibiotics. However, further analysis should be performed to ensure the patient’s ability to take oral medications and the availability of outpatient support. Scores of 2 or greater require hospitalization, and those of 3 or greater should be assessed for intensive care unit (ICU) admission. Patients with a score of 3 or greater have a 30-day mortality of 15% to 40%. Compared to PSI, CURB-65 assigns no points to comorbid illnesses; another limitation of CURB-65 is that it assumes that the confusion is related to the acute pneumonia.

Although outpatients usually are diagnosed and empiric therapy is started based on clinical findings, further diagnostic evaluation is necessary in hospitalized patients. Chest radiography is required to diagnose CAP, to define the extent of the pneumonia, and to look for complications, such as parapneumonic effusion or lung abscess. Unless the patient cannot mount an immune response, as in severe neutropenia, significant dehydration, or early in the disease process, every patient with pneumonia will have a visible pulmonary consolidation.

Imaging. The pattern of infiltration can yield diagnostic clues. Infection with S. pneumoniae classically presents with a dense lobar consolidation, often with an associated parapneumonic effusion. Diffuse interstitial opacities are common in Pneumocystis pneumonia and viral processes. Conversely, pleural effusions are almost never seen in Pneumocystis pneumonia. Bilateral apical alveolar opacities (with or without cavitation) suggest tuberculosis. Appearance of cavitation suggests a necrotizing infection such as S. aureus, tuberculosis, or gram-negative organisms like P. aeruginosa or Klebsiella pneumoniae. Serial chest radiography of inpatients usually is unnecessary because many weeks are required for the infiltrate to resolve; serial chest radiography typically is performed if the patient does not show clinical improvement, has a pleural effusion, or has a necrotizing infection. Infiltrates that are not resolving or that are relapsing on the same lung field represent a red flag for obstruction of the bronchus corresponding with that area; malignancy is usually the culprit.

Laboratory Results. Microbiologic studies, such as blood cultures and sputum Gram stain and culture, should be obtained to try to establish the etiology. Sputum samples are frequently contaminated by oral flora, limiting their value, though their diagnostic yield increases when sputum is purulent (> 25 polymorphonuclear cells and < 10 epithelial cells per low-power field). Additionally, blood cultures can further classify the etiology of pneumonia, especially since 30% to 40% of pneumococcal pneumonia patients are bacteremic on admission. Further serologic studies can diagnose patients who are infected with organisms not easily cultured, for example, Legionella, Mycoplasma, or C. pneumoniae.

Bronchoscopy. Finally, fiber-optic bronchoscopy with bronchoalveolar lavage is often performed in seriously ill patients, the immunocompromised, and patients who are not responding to therapy. This procedure obtains specimens from the lower respiratory tract for routine Gram stain and culture, as well as direct fluorescent antibody testing for organisms such as Legionella or P. jiroveci.

Treatment

Initially, empiric treatment is based on the most common organisms given the clinical scenario. Macrolide antibiotics (azithromycin), doxycycline, or antipneumococcal fluoroquinolones (moxifloxacin or levofloxacin) are good choices for outpatient treatment of CAP caused by S. pneumoniae, M. pneumoniae, and other common bacterial organisms. Keep in mind that increasing community resistance patterns alter available antibiotic coverage. In regard to outpatient therapy duration, antibiotics should be administered for a minimum of 5 days. Hospitalized patients with CAP usually require intravenous third-generation cephalosporin plus a macrolide (or antipneumococcal fluoroquinolone). For immunocompetent patients with hospital-acquired or ventilator-associated pneumonias, initial antibiotic coverage is broader, with more serious antibiotic coverage. Some common antimicrobials chosen include piperacillin-tazobactam, cefepime, levofloxacin, imipenem, or meropenem. In addition, for patients with risk factors for MRSA infection (ie, prior intravenous antibiotic use, intravenous drug usage, recent ventilatory support), empiric coverage for MRSA such as vancomycin or linezolid should be added. Vaccination for influenza and pneumococcus should be considered for all who meet the criteria. Smoking cessation is also an integral part of postrecovery care.

Other Pulmonary Syndromes

Three other commonly confused pulmonary syndromes deserve mention at this point: aspiration pneumonia, chemical pneumonitis, and mechanical obstruction.

Aspiration Pneumonia. Aspiration pneumonia refers to the inflammation promoted by infectious agents that results from abnormal entry of fluids or secretions into the lower airways when defensive mechanisms of the upper airway fail. It should be noted that many healthy adults frequently aspirate small volumes of oropharyngeal secretions while sleeping (this is the primary way that bacteria gain entry to the lungs), but the material is cleared by coughing, ciliary transport, or normal immune defenses so that no clinical infection results. The affected lobe of the lung depends on the patient’s position: In recumbent patients, the posterior segments of the upper lobes and superior segments of the lower lobes are most common.

Chemical Pneumonitis. Chemical pneumonitis refers to the aspiration of toxic substances (the most common being gastric acid) into the lower airway without the development of bacterial infection. The inflammation is proportional to the volume of the aspirate and the acidity of the content. The clinical presentation can go from minor dyspnea and low-grade fever to severe respiratory distress and a pulmonary infiltrate that is apparent within 4 to 6 hours and typically resolves within 48 hours. Aspiration of gastric contents is most likely to occur in patients with a depressed level of consciousness, such as with anesthesia, drug overdose, intoxication, or a postictal state. This process has also been described among victims of smoke inhalation. Treatment for chemical pneumonitis is usually supportive and involves positive pressure breathing, intravenous fluids, and tracheal suction.

Infectious pneumonia should be considered in those who fail to show clinical improvement after 48 hours of presumed chemical pneumonitis; those with significant comorbidities can be started on antibiotics initially. In contrast to chemical pneumonitis, where aspiration of vomitus may be witnessed, the aspiration of oral secretions typically is silent and should be suspected when any institutionalized patient with dysphagia presents with respiratory symptoms and pulmonary infiltrate in a dependent segment of the lung.

Antibiotic therapy for presumed bacterial aspiration (infectious) pneumonia is similar to that of other pneumonias; antibiotics should cover typical respiratory pathogens such as oral anaerobes, gram-negative organisms, S. pneumoniae, and H. influenzae. When anaerobes are likely, first-line therapy is ampicillin-sulbactam, amoxicillin-clavulanate, or the combination of metronidazole plus amoxicillin or penicillin G. Clindamycin use has declined secondary to increased resistance; however, it can still be used in those with penicillin allergies.

Airway Obstruction. Airway obstruction refers to the inhalation of nontoxic fluid or matter causing obstruction or closure of distal airways. The most common aspirated items include water, saline, barium, and food. The fluids/matter can result in a reversible hypoxemia. Treatment involves removal of the obstruction with supportive care.

CASE CORRELATION

• See also Case 14 (Pulmonary Embolism), Case 15 (Chronic Obstructive Pulmonary Disease), Case 16 (Chronic Cough/Asthma), Case 17 (Pleural Effusion, Parapneumonic), and Case 18 (Hemoptysis/Lung Cancer).

COMPREHENSION QUESTIONS

19.1 A 65-year-old man with a medical history of uncontrolled hypertension, mild biventricular systolic heart failure, and a 40 pack-year smoking history presents to the emergency room with 1 week of worsening cough, fever, and dyspnea at rest. His symptoms also include diffuse myalgia, abdominal pain, nonbloody diarrhea, and a rapidly worsening nonproductive cough. He denies alcohol or drug history and endorses being married to his wife for 40 years. On admission, his vital signs are: temperature of 38 °C, blood pressure (BP) 160/82 mm Hg, heart rate 89 beats per minute (bpm), respiratory rate (RR) 25 breaths/min, and SpO2 (oxygen saturation as measured by pulse oximetry) is 94% on room air. Which of the most likely organisms is the etiology of his illness?

A. Aspergillus fumigatus

B. Chlamydia pneumoniae

C. Coccidioidomycosis

D. Legionella pneumophila

E. Mycoplasma pneumoniae

19.2 An 85-year-old nursing home resident with a medical history of diastolic heart failure, hypertension, diabetes mellitus, and dementia requiring assistance in all activities of daily life presents with a 3-day history of fever and nonbloody, productive cough. Her mental status was found to be more altered than usual. On admission, her vital signs show the following: temperature of 39 °C, BP 105/70 mm Hg, heart rate 93 bpm, RR 32 breaths/min, and SpO2 94% on room air. Chest x-ray reveals a right middle lobe consolidation. Which of the following is the best medical treatment of the patient?

A. Admit to the floor and start intravenous cefepime and linezolid.

B. Admit to the floor and start intravenous azithromycin and ceftriaxone.

C. Admit to the ICU and start intravenous vancomycin and linezolid.

D. Discharge home with a prescription of oral amoxicillin and cefpodoxime.

E. Discharge home with oral azithromycin and oral cefpodoxime.

19.3 A 56-year-old man with a medical history of hypertension, chronic kidney disease stage III, gout, and alcohol dependence is brought in by emergency medical services after being found down on the ground. He smells strongly of ethanol and has a prior history of delirium tremens based on previous medical records. He is admitted to the ICU with concern for alcohol withdrawal. His vitals on admission are: temperature 37 °C, BP 110/74 mm Hg, heart rate 77 bpm, RR 12 breaths/min, and SpO2 of 94% on room air. Due to concern for inability to protect his airway, he is intubated in the emergency room. The next day, he shows significant clinical improvement and is extubated. Later that day, he goes into withdrawal with altered mental status, and aspirates while eating. What is the next best step in management?

A. Obtain chest x-rays and continue to monitor for symptoms.

B. Obtain chest x-rays and start azithromycin therapy.

C. Obtain chest x-rays and start vancomycin and cefepime.

D. Obtain chest x-rays, perform bronchoscopy, and initiate steroid treatment.

ANSWERS

19.1 D. Legionella typically presents with diffuse myalgias, abdominal pain, diarrhea, and severe pneumonia. Tobacco dependence increases susceptibility to Legionella as well. Typically, it is associated with hyponatremia on laboratory tests. C. pneumoniae (answer B) typically presents in older patients with more indolent symptoms and associated pharyngitis, hoarseness, and/or sinus involvement. M. pneumonia (answer E) tends to appear in young adults, with significantly fewer toxic symptoms; this is why it is also known as walking pneumonia. Bullous myringitis (blisters seen on the tympanic membrane) is frequently associated. Coccidioidomycosis (answer C) is endemic in the southwestern United States and causes a subclinical infection, often after dust exposure. Aspergillus (answer A) is more common in immunocompromised individuals and can present with hemoptysis and lung infarction.

19.2 B. This nursing home resident would be considered to have CAP, with a similar infectious rate as individuals not residing in nursing homes. Using CURB-65, the patient would have three points (confusion for her worsening mental status, respiratory rate > 30 breaths/min, and her age). These criteria indicate the need for hospitalization with possible consideration for ICU admission; thus, discharging this patient home (answers D and E) would be inappropriate. The use of ceftriaxone (or other third-generation cephalosporins) and azithromycin would be appropriate therapy. Vancomycin and linezolid (answer C) cover gram-positive organisms only.

19.3 A. The patient did aspirate; however, this does not automatically mean aspiration pneumonia will develop. The first steps are to obtain imaging and monitor closely. If symptoms (fevers or purulent sputum production) develop or the patient fails to improve after 48 hours, then ampicillin-sulbactam, amoxicillin-clavulanate, or metronidazole plus amoxicillin can be started to cover anaerobic mouth bacteria. Azithromycin (answer B) is indicated for CAP but is not the appropriate therapy for aspiration pneumonia. Vancomycin and cefepime (answer C) would not need to be started unless necrotizing pneumonia is suspected. Last, bronchoscopy (answer D) is typically not required for aspiration pneumonitis diagnosis, and steroids are not used.

CLINICAL PEARLS

▶ It is difficult to reliably distinguish clinically between typical and atypical causes of pneumonia. Therefore, diagnosis and empiric treatment of pneumonia are based on the setting in which it was acquired (CAP or HCAP) and the immune status of the host.

▶Clinical criteria, such as patient’s age, vital signs, mental status, renal function, and additional comorbidities can be used to risk stratify patients with pneumonia to decide who can be treated as an outpatient and who requires hospitalization with intravenous antibiotics.

▶Although initial antibiotic therapy is empiric, the etiologic agent frequently can be identified based on chest radiography, blood cultures, or sputum Gram stain and culture. Once determined, antibiotics can be deescalated for more specific coverage.

▶Chemical pneumonitis is a noninfectious, chemically induced inflammation caused by inhalation of acidic gastric contents in patients with a decreased level of consciousness, such as seizure or overdose; however, if patients fail to improve within 48 hours, antibiotic interventions can be started. It can also be seen in victims of smoke inhalation.

▶Aspiration (infectious) pneumonia is a pulmonary infection caused by aspiration of colonized oropharyngeal secretions and is seen in patients with impaired swallowing, such as stroke victims. The treatment is antibiotics.

REFERENCES

Bartlett JG. How important are anaerobic bacteria in aspiration pneumonia: when should they be treated and what is optimal therapy. Infect Dis Clin North Am. 2013;27(1):149. 

Kalil AC, Metersky ML, Klompas M, et al. Management of adults with hospital-acquired and ventilator-associated pneumonia: 2016 clinical practice guidelines by the Infectious Diseases Society of America and the American Thoracic Society. Clin Infect Dis. 2016;63(5):e61. 

Kumar ST, Yassin A, Tanaya B, et al. Recommendations from the 2016 guidelines for the management of adults with hospital-acquired or ventilator-associated pneumonia. P T. 2017;42(12):767-772. 

Mandell LA, Wunderink R. Pneumonia. In: Jameson JL, Fauci AS, Kasper DL, et al, eds. Harrison’s Principles of Internal Medicine. 20th ed. New York, NY: McGraw Hill; 2018. 

Ost D, Fein A, Feinsilver SH. Nonresolving pneumonia. Post TW, ed. UpToDate. Waltham, MA: UpToDate; 2019 https://www.uptodate.com/contents/diagnostic-evaluation-of-the-incidental- pulmonary-nodule. Accessed June 17, 2019. 

Yealy DM, Fine MJ. Community-acquired pneumonia in adults: Assessing severity and determining the appropriate site of care. Post TW, ed. UpToDate. Waltham, MA: UpToDate; 2019 https://www .uptodate.com/contents/community-acquired-pneumonia-in-adults-assessing-severity-and-determining-the-appropriate-site-of-care. Accessed July 21, 2019.

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