Bacterial Pneumonia

Numbers (% or LR)
Prevalence
1. In the ED with acute respiratory symptoms (before chest x-ray) 4%
2. Outpatients seen in clinic 2%
Risk Factor
1. Age ≥ 65 LR 3
2. History of stroke or dementia LR 3
3. Immunocompromised LR 3
4. Other chronic comorbidity (i.e. COPD, CKD) LR 1.5
Symptoms/Syndrome
1. Fever LR 3
2. TachypneaLR 3
3. HypoxemiaLR 3
4. Crackles or rales on chest exam LR 1.5
5. Alternative cause of symptoms LR 0.5
TestClinical sensitivityClinical specificity
1. Chest x-ray65% 70%
2. CT chest98% 75%
3. Sputum / lower respiratory tract culture*30% 90%
4. Respiratory viral testing**40% 52%
5. Procalcitonin 0.5 µg/L55% 76%
*Depends on specimen type and quality, means of collection, and whether it is collected from a source that is expected to be contaminated, like an endotracheal tube that is known to be colonized.
**An indirect test for bacterial pneumonia. Bacterial/viral co-infection is possible.
Other
Explanation for + test without disease:
Chest CT: viral pneumonia, fungal pneumonia, malignancy, pulmonary edema, autoimmune/inflammatory pneumonia
Lower respiratory culture: bacterial colonization, contamination
Explanation for - test with disease:
Chest CT: early/developing disease, dehydration, poor quality study
Lower respiratory culture: poor quality specimen, sampling from uninvolved area of lung, overgrowth of “normal respiratory flora”
Example of high value use:
Deciding whether to obtain chest imaging or sputum culture for a patient with moderate pre-test probability of community-acquired pneumonia
Example of low value use:
Considering advanced imaging in a patient with an equivocal chest radiograph and low pre-test probability of disease.
Choosing wisely:
1. Don’t initiate empiric antibiotic therapy in the patient with suspected invasive bacterial infection without first confirming that blood, urine or other appropriate cultures have been obtained, excluding exceptional cases.
2. Don’t treat uncomplicated community-acquired pneumonia in otherwise healthy, immunized, hospitalized patients with antibiotic therapy broader than ampicillin.

Discussion

Incidence of Community-Acquired Bacterial Pneumonia:

The incidence of bacterial lower respiratory tract infection in the overall population of healthy US adults is expected to be very low. Annual incidence of community-acquired pneumonia is estimated to be 24.8 cases per 10,000 person-years, and a substantial proportion of community-acquired pneumonia is likely due to viral infection.[1]

The incidence of bacterial lower respiratory tract infection is likely higher among the population of individuals seeking healthcare for acute respiratory illness. In the emergency department, 10-12% of adults with acute cough will be diagnosed with pneumonia.[2,3] When multiple vital sign abnormalities are present, the incidence may be as high as 69%.[4] In the outpatient clinic setting, about 6% of adults presenting with cough will be diagnosed with pneumonia.[3]

Among patients being admitted to the hospital with pneumonia, 38% will have microbiologically confirmed infection, including 14% with bacterial infection, 23% with viral infection, and 1% with fungal or mycobacterial pathogens.[1] Thus, 37% of microbiologically confirmed cases of community-acquired pneumonia have a bacterial etiology. Assuming that a pathogen is present but undetected in most of the cases with an unknown etiology, we estimated that about 1/3 of patients diagnosed with community-acquired pneumonia have a bacterial lower respiratory infection. Thus, the incidence of bacterial lower respiratory tract infection is 4% in the ED and 2% in the outpatient clinic.

Risk Factors:

Age, history of stroke or dementia, and immunocompromised status moderately increase likelihood of bacterial lower respiratory tract infection.[4-6] Other chronic illnesses were considered minor risk factors, since they may increase likelihood of multiple syndromes which can present with acute cough and dyspnea.[7,8] Chronic obstructive pulmonary disease (COPD has been associated with pneumonia but more commonly causes chronic bronchitis. Chronic kidney disease (CKD) has been associated with pneumonia but may also cause volume overload and pulmonary edema

Symptoms/Syndromes:

Risk scores have previously assessed the impact of specific signs and symptoms on the likelihood of community-acquired pneumonia.[3,9-12] Symptoms that appear in multiple predictive models as increasing the likelihood of bacterial lower respiratory tract infection include fever, tachypnea, hypoxemia, and crackles or rales on chest exam. Among these, all were graded as moderately increasing likelihood of bacterial lower respiratory tract infection except for abnormal chest exam, which is a subjective finding and therefore may be difficult to reproduce.

Due to the nonspecific nature of symptoms of bacterial pneumonia, direct likelihood ratios could not be determined. Utilizing Huijskens et al’s published data regarding frequency of symptoms in bacterial pneumonia, likelihood ratios were estimated as above.[6]

Test sensitivity & specificity:

FThe sensitivity and specificity of chest x-ray in the diagnosis of community-acquired bacterial pneumonia were determined based on an average of estimates across multiple studies comparing diagnostic accuracy in comparison to chest CT.[13-17]

Given that imaging by chest CT is considered the gold standard test for diagnosis of community-acquired pneumonia, the sensitivity of chest CT was estimated to be near 100%.[15,18] However, in recognition that chest CT may be falsely negative early in disease, if the patient is dehydrated, or in the context of a low-quality exam, the sensitivity of chest CT was downgraded to 99%. The specificity of chest CT was set at 80% based on comparison between chest CT and clinical diagnosis of pneumonia, as determined by an expert adjudication committee, evidence that 22% of results from chest CT are considered uncertain.[14,19]

The performance characteristics of sputum culture were difficult to assess. Published studies typically evaluate the sensitivity and specificity of sputum culture for the identification of specific organisms, such as Streptococcus pneumoniae, rather than as a test that can be used to diagnose any bacterial etiology of disease.[20-22] There is also ambiguity in whether a sputum culture that grows “normal respiratory flora” should be considered positive or negative.[23] In consideration of these areas of uncertainty, the sensitivity of sputum culture was approximated by the diagnostic yield of sputum culture.[22,24] The specificity of sputum culture was estimated based on an average of estimated specificity when identifying the most common bacterial pathogens in community-acquired disease.[20,21] The specificity of lower respiratory culture is expected to be lower among hospitalized patients with endotracheal tubes or patients with chronic structural lung disease.

References

  1. Jain S, Self WH, Wunderink RG, et al. Community-Acquired Pneumonia Requiring Hospitalization among U.S. Adults. N Engl J Med. 2015;373(5):415-427.

  2. Flanders SA, Stein J, Shochat G, et al. Performance of a bedside C-reactive protein test in the diagnosis of community-acquired pneumonia in adults with acute cough. Am J Med. 2004;116(8):529-535.

  3. Emerman CL, Dawson N, Speroff T, et al. Comparison of physician judgment and decision aids for ordering chest radiographs for pneumonia in outpatients. Ann Emerg Med. 1991;20(11):1215-1219.

  4. Nolt BR, Gonzales R, Maselli J, Aagaard E, Camargo CA, Jr., Metlay JP. Vital-sign abnormalities as predictors of pneumonia in adults with acute cough illness. Am J Emerg Med. 2007;25(6):631-636.

  5. Huijskens EGW, Koopmans M, Palmen FMH, van Erkel AJM, Mulder PGH, Rossen JWA. The value of signs and symptoms in differentiating between bacterial, viral and mixed aetiology in patients with community-acquired pneumonia. J Med Microbiol. 2014;63(3):441-452.

  6. Kishore AK, Vail A, Chamorro A, et al. How is pneumonia diagnosed in clinical stroke research? A systematic review and meta-analysis. Stroke. 2015;46(5):1202-1209.

  7. Müllerova H, Chigbo C, Hagan GW, et al. The natural history of community-acquired pneumonia in COPD patients: a population database analysis. Respir Med. 2012;106(8):1124-1133.

  8. Chou C-Y, Wang S-M, Liang C-C, et al. Risk of Pneumonia Among Patients With Chronic Kidney Disease in Outpatient and Inpatient Settings: A Nationwide Population-Based Study. Medicine. 2014;93(27):e174.

  9. Metlay JP, Kapoor WN, Fine MJ. Does This Patient Have Community-Acquired Pneumonia?: Diagnosing Pneumonia by History and Physical Examination. JAMA. 1997;278(17):1440-1445.

  10. Heckerling PS, Tape TG, Wigton RS, et al. Clinical prediction rule for pulmonary infiltrates. Ann Intern Med. 1990;113(9):664-670.

  11. Singal BM, Hedges JR, Radack KL. Decision rules and clinical prediction of pneumonia: evaluation of low-yield criteria. Ann Emerg Med. 1989;18(1):13-20.

  12. Gennis P, Gallagher J, Falvo C, Baker S, Than W. Clinical criteria for the detection of pneumonia in adults: guidelines for ordering chest roentgenograms in the emergency department. J Emerg Med. 1989;7(3):263-268.

  13. Karimi E. Comparing Sensitivity of Ultrasonography and Plain Chest Radiography in Detection of Pneumonia; a Diagnostic Value Study. Arch Acad Emerg Med. 2019;7(1):e8-e8.

  14. Makhnevich A, Sinvani L, Cohen SL, et al. The Clinical Utility of Chest Radiography for Identifying Pneumonia: Accounting for Diagnostic Uncertainty in Radiology Reports. American Journal of Roentgenology. 2019;213(6):1207-1212.

  15. 15. Syrjälä H, Broas M, Suramo I, Ojala A, Lähde S. High-resolution computed tomography for the diagnosis of community-acquired pneumonia. Clin Infect Dis. 1998;27(2):358-363.

  16. 16. Claessens YE, Debray MP, Tubach F, et al. Early Chest Computed Tomography Scan to Assist Diagnosis and Guide Treatment Decision for Suspected Community-acquired Pneumonia. Am J Respir Crit Care Med. 2015;192(8):974-982.

  17. Self WH, Courtney DM, McNaughton CD, Wunderink RG, Kline JA. High discordance of chest x-ray and computed tomography for detection of pulmonary opacities in ED patients: implications for diagnosing pneumonia. The American journal of emergency medicine. 2013;31(2):401-405.

  18. Hayden GE, Wrenn KW. Chest radiograph vs. computed tomography scan in the evaluation for pneumonia. The Journal of emergency medicine. 2009;36(3):266-270.

  19. Prendki V, Scheffler M, Huttner B, et al. Low-dose computed tomography for the diagnosis of pneumonia in elderly patients: a prospective, interventional cohort study. Eur Respir J. 2018;51(5):1702375.

  20. Fukuyama H, Yamashiro S, Kinjo K, Tamaki H, Kishaba T. Validation of sputum Gram stain for treatment of community-acquired pneumonia and healthcare-associated pneumonia: a prospective observational study. BMC Infect Dis. 2014;14:534-534.

  21. Del Rio-Pertuz G, Gutiérrez JF, Triana AJ, et al. Usefulness of sputum gram stain for etiologic diagnosis in community-acquired pneumonia: a systematic review and meta-analysis. BMC Infect Dis. 2019;19(1):403-403.

  22. gawa H, Kitsios GD, Iwata M, Terasawa T. Sputum Gram Stain for Bacterial Pathogen Diagnosis in Community-acquired Pneumonia: A Systematic Review and Bayesian Meta-analysis of Diagnostic Accuracy and Yield. Clinical infectious diseases : an official publication of the Infectious Diseases Society of America. 2020;71(3):499-513.

  23. Musher DM, Jesudasen SJ, Barwatt JW, Cohen DN, Moss BJ, Rodriguez-Barradas MC. Normal Respiratory Flora as a Cause of Community-Acquired Pneumonia. Open Forum Infect Dis. 2020;7(9):ofaa307.

  24. García-Vázquez E, Marcos MA, Mensa J, et al. Assessment of the Usefulness of Sputum Culture for Diagnosis of Community-Acquired Pneumonia Using the PORT Predictive Scoring System. Arch Intern Med. 2004;164(16):1807-1811.

 Authors: Jon Baghdadi, Ravi Tripathi, Daniel Morgan