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Community acquired pneumonia ( CAP )

Pneumonia is an infection of the pulmonary parenchyma caused by various organisms. The book also states that pneumonia is not a single disease but a group of specific infections , each with a different epidemiology , pathogenesis , presentation and clinical course ( Harrison’s textbook of medicine )

Our discussion here is focused on community-acquired pneumonia ( CAP )
How common –Community acquired pneumonia (CAP ) causes great mortality and morbidity and high costs worldwide ( Lancet 2015 ) WHO reports that pneumonia accounts for 15 % of all deaths of children under 5 killing 808 694 children in 2017
( Pneumonia remains the single largest infectious cause of death in children worldwide ) WHO data from 2015 shows that 3.2 million of the 56.4 million deaths in 2015 were caused by LRTIs making them the most deadly communicable disease and 3rd largest cause of mortality It is well known that CAP remains the main cause of death from infectious disease globally Streptococcus pneumoniae ( pneumococcus ) is the most frequent causative pathogen of CAP regardless of setting The Global disease study 2015 stated that LRTIs are the 3rd most common cause of death globally after IHD and Cerebrovascular disease NICE reports that 
- every year between 0.5 % and 1 % of adults in the UK would suffer with CAP
- pneumonia is diagnosed in 5 % to 12 % of adults who present to GPs with symptoms of LRTI – of these about 22-42 % would be hospitalized where the mortality rate varies between 5-14 %
- more than 1/2 of pneumonia related deaths happen in people over 84 HOP ( hospital acquired pneumonia ) affects 1.5 % of hospitalized patients in England & this increases the hospital stay by about 8 days and with a mortality rate ranging from 30-70 %
Bacteria-Streptococcus pneumoniae Haemophilus influenzae Atypical pathogens
- Mycoplasma pneumoniae– Chlamydophila pneumoniae– Coxiella burnetii– Legionella pneumophilia
Viruses -Influenza viruses A & B Rhinoviruses Parainfluenza viruses 1, 2 & 3 Coronaviruses Metapneumovirus Respiratory syncytial virus
Others- Aspiration pneumonia Hematogenous spread Multi-drug resistant bacterial most commonly MRSA , P aeruginosa , Acinetobacter baumanni and various Enterobacteriaceae species Hematogenous spread
microbial diagnosis of pneumonia is achieved in < 50 % of cases 
( ie in 1/2 the cases of pneumonia the etiology remains unknown ) globally Streptococcus pneumoniae is the most common pathogen responsible for CAP Viral causes ( 10-22 % ) and atypical pathogens ( 11-28 % ) are also common causes of CAP – among the viruses respiratory syncytial virus is the most common cause of pneumonia
Risk factors -Age > 65 Smoking Alcoholism Immunosuppressive conditions COPD Cardiovascular disease Cerebrovascular disease Chronic liver or renal disease Diabetes mellitus Dementia , Recent viral upper respiratory tract infection Functional impairment Previous CAP Poor dental health Oral steroids Treatment with gastric suppressive agents Contact with children Low body mass index Crowded situations Dysphagia
Aspiration pneumonia
 may be frequently underestimated particularly in elderly , most common 
pathogens are anaerobic 
bacteria and microaerophilic streptococci
 from the oral 
Pneumonia is defined by Progressive infiltrate found on CXR / CT PLUS

Two or more of the following fever sputum production rhinorrhoea sore throat dyspnea. Most patients present with a h/o cough , dyspnoea , pleuritic pain , fever or chills and malaise.
NICE recommends using the CRB 65 score in primary care by giving 1 point each for. 0-Low risk with < 1 % mortality risk.
1-Intermediate risk with 1-10 % mortality risk.
2-High risk with more than 10 % mortality risk
Oxford COVID 19 Evidence has made the following recommendations for rapid diagnosis of community acquired pneumonia auscultation is not essential if overall clinical judgement of CAP is already met ( partly based on temp ≥ 38 , RR > 20 , PR > 100 and new confusion ) auscultation / BP – consider if it is crucial to decision making for e.g to admit or not.
Pneumonia severity index ( PSI ) is another scoring system which can assess the severity of community acquired pneumonia and determine admission status ( Points scored indicate severity – use MDCALC website to access PSI )
Minor criteria -RR ≥ 30 /min PaO2/ FiO2 ratio < 250 Multilobar infiltrates Confusion / disorientation Uremia ( blood urea nitrogen level ≥ 20 mg/ dl Leukopenia ( WBC < 4000 cells / µl ) Thrombocytopenia ( platelet count < 100 000 /µl ) Hypothermia Hypotension requiring aggressive fluid < 36 C management
Major criteria -Septic shock with need for vasopressors Respiratory failure requiring mechanical ventilation
Crp -< 100 is independently associated with a lower mortality and > 100 mg /dl with increased risk of complications provides additional prognostic data
Urine antigen test –Pneumococcal urinary antigen test -is a simple and rapid immunochromatographic membrane test ( ICT ) test to detect pneumococcal cell wall polysaccharide substantial advantage over sputum -diagnostic yield and the ability to establish the diagnosis after antibiotic treatment studies have shown a sensitivity of 82 % and specificity of of 97 % ( these are less in children and in adults with non-bacteremia pneumonia )
CXR -interstitial / alveolar/ lobar / air bronchogram dense fluffy consolidation of entire lung or portion of a lobe often with air bronchograms and possible pleural effusion
Serology -blood , urine , NPS ( Legionella , S pneumoniae ) serological testing for atypical pathogens testing for specific pathogens is not indicated in primary care. It is needed if the result would alter the standard empiric therapy PCR can detect several viruses several rapid diagnostic tests are available which can be applied at the point of care for S. Pneumoniae , Legionella and influenza ( e.g Rapid Influenza Diagnostic Tests )
Ultrasound -subpleural consolidation B lines pleural line abnormalities pleural effusion air bronchogram lung US has better potential at diagnosing pneumonia , pneumothorax , pulmonary embolism and pulmonary contusions
Expectorated sputum -most readily available specimen subject to oropharyngeal contamination no easy method available to distinguish common pathogens from normal flora with Gram stain or selective media false positive and false negative results are possible use in diagnosis is controversial and ensuring good quality sputum from the lower respiratory tract is essential
Procalcitonin- useful biomarker of severe CAP can help reduce unnecessary antibiotic exposure
Blood culture -before start of antibiotic therapy has high specificity but only positive in less than 20 % of cases higher yield in severe CAP.
Chest CT is the most sensitive way of identifying infectious involvement of the lung parenchyma Particularly useful in obese patients , immunosuppressed patients , people with previous abnormal radiological findings , suspected fungal infections and excluding other diagnoses
Guidance on management -before start of antibiotic therapy has high specificity but only positive in less than 20 % of cases higher yield in severe CAP
Guideline on prescribing antibiotics has been published by NICE for both community and hospital acquired pneumonia. These have been summarized on A4Medicine
Recommendations from the American Thoracic Society and Infectious Diseases Society of America

The following is a summary of recommendations which may be useful in addition to the NICE guidance for managing CAP
Gram staining , culture or blood culture are not recommended on outpatient setting Routine urine testing for pneumococcal antigen is not indicated except in severe CAP Routine urine testing for Legionella antigen is not indicated except in situations like Legionella outbreak or severe CAP They suggest testing for influenza with a rapid influenza molecular assay during an outbreak The guideline recommends using empiric antibacterial therapy in adults with suspected and radiographically confirmed CAP regardless of the serum procalcitonin level For judging the prognosis of the illness the guideline recommends use of a validated clinical prediction rule as the Pneumonia Severity Index over CURB 65 The guideline recommend antibiotic for CAP as below
No comorbidities or risk factors for Pseudomonas aeruginosa –Amoxicillin or Doxycycline or Macrolide if the local pneumococcal resistance is < 25 % Risk factors for Pseudomonas aeruginosa include previous isolation of MRSA or or P.aeuriginosa or recent hospitalization and use of parenteral antibiotics Co-morbidities include chronic heart , lung , liver or renal disease , diabetes , alcoholism , malignancy or asplenia
With co-morbidities -Combination therapy with amoxicillin / cluvanate or cepalosporin 
macrolide or doxycycline

or monotherapy with respiratory fluoroquinolone for e.g Levofloxacin 750 mg od , moxifloxacin 400 mg daily or gemifloxacin 320 mg daily

  1. Diagnosis and Treatment of Adults with Community-acquired Pneumonia. An Official Clinical Practice Guideline of the American Thoracic Society and Infectious Diseases Society of America  Journal Article  2019  American Journal of Respiratory and Critical Care Medicine PG – e45-e67 VI – 200 IP – 7 AID – 10.1164/rccm.201908-1581ST [do] PMID – 31573350 4099 – 4100 –
  2. Microbial Etiology of Pneumonia: Epidemiology,
    Diagnosis and Resistance Patterns Catia Cilloniz 1 , Ignacio Martin-Loeches 2
    , Carolina Garcia-Vidal 3 , Alicia San Jose 1 and Antoni Torres 1 Int. J. Mol. Sci. 2016, 17, 2120; doi:10.3390/ijms17122120
  3. Lecture Community-acquired pneumoniaJeremy S Brown Clinical Medicine 2012, Vol 12, No 6: 538–543
  4. Pneumonia statistics British Lung Foundation
  5. Pneumonia in adults NG 110 2016
  6. Rapid diagnosis of community-acquired pneumonia for clinicians March 20, 2020 Oxford Covid-19 Evidence Service
  7. Muthumbi, E., Lowe, B.S., Muyodi, C. et al. Risk factors for community-acquired pneumonia among adults in Kenya: a case–control study. Pneumonia 9, 17 (2017).
  8. Torres APeetermans WEViegi G, et al
    Risk factors for community-acquired pneumonia in adults in Europe: a literature review
  9. Almirall J, Serra-Prat M, Bolíbar I, Balasso V: Risk Factors for Community-Acquired Pneumonia in Adults: A Systematic Review of Observational Studies. Respiration 2017;94:299-311. doi: 10.1159/000479089
  10. RESEARCH ARTICLE Pneumonia severity index in viral community
    acquired pneumonia in adults Mi-Ae Kim1 , Jae Seok Park1 , Choong Won Lee2
    , Won-Il ChoiI PLOS ONE | March 6, 2019
  11. Laboratory diagnosis of pneumonia in the molecular age
    Antoni TorresNelson LeeCatia CillonizJordi VilaMenno Van der Eerden
  12. Cillóniz CEwig SPolverino E, et al
    Microbial aetiology of community-acquired pneumonia and its relation to severity
  13. Etiology of Community-Acquired Pneumonia:
    Impact of Age, Comorbidity, and Severity
    Department of Medicine, University of Barcelona, Barcelona, Spain Am J Respir Crit Care Med Vol 160. pp 397–405, 1999
    Internet address:
  14. Challenges of diagnosing and managing pneumonia in primary care Nursing Times [online] September 2019 / Vol 115 Issue 9
  15. 2018 recommendations for the management
    of community acquired pneumonia J Bras Pneumol. 2018;44(5):405-423
  16. Community-acquired pneumonia:
    Strategies for triage and treatment Anita R. Modi, MD
    Department of Infectious Disease,
    Cleveland Clinic
    Christopher S. Kovacs, MD
    Department of Infectious Disease, Cleveland Clinic;
    Assistant Professor, Cleveland Clinic Lerner College
    of Medicine of Case Western Reserve University,
    Cleveland, OH
  17. Pneumonia WHO Factsheet
  18. Cillóniz, Catia, Celia Cardozo, & Carolina García-Vidal. “Epidemiology, pathophysiology, and microbiology of communityacquired pneumonia.” Annals of Research Hospitals [Online], 2.1 (2018): n. pag. Web. 19 Nov. 2020



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