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== Laboratory Findings ==
== Laboratory Findings ==
{| class="wikitable"
|-
! style="width: 50%;" | '''Rapid antigen detection test'''
! style="width: 50%;" | '''Throat culture'''
|-
| valign = top |
'''Advantages'''<br>
* Rapidity of the test: Rapid identification and treatment of patients with GAS pharyngitis can reduce the risk of spread, allowing the patient to return to school or work sooner, and can reduce the acute associated morbidity.<ref name="pmid3923180">Randolph MF, Gerber MA, DeMeo KK, Wright L (1985) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=3923180 Effect of antibiotic therapy on the clinical course of streptococcal pharyngitis.] ''J Pediatr'' 106 (6):870-5. PMID: [https://pubmed.gov/3923180 3923180]</ref>
* High specificity: RADTs currently available are highly specific (approximately 95%) when compared with blood agar plate cultures.<ref name="pmid2687791">Gerber MA (1989) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=2687791 Comparison of throat cultures and rapid strep tests for diagnosis of streptococcal pharyngitis.] ''Pediatr Infect Dis J'' 8 (11):820-4. PMID: [https://pubmed.gov/2687791 2687791]</ref>
* False positive test results are highly unusual, and therefore therapeutic decisions can be made with confidence on the basis of a positive test result.<ref name="pmid15258094">Gerber MA, Shulman ST (2004) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=15258094 Rapid diagnosis of pharyngitis caused by group A streptococci.] ''Clin Microbiol Rev'' 17 (3):571-80, table of contents. [http://dx.doi.org/10.1128/CMR.17.3.571-580.2004 DOI:10.1128/CMR.17.3.571-580.2004] PMID: [https://pubmed.gov/15258094 15258094]</ref>
'''Disadvantages'''<br>
* Sensitivity is low: Because the sensitivities of the various RADTs are <90% and because the proportion of acute pharyngitis due to GAS in children and adolescents is sufficiently high (20%-30%), a negative RADT should be accompanied by a follow-up or back-up throat culture in children and adolescents, while this is not necessary in adults under usual circumstances.<ref name="pmid15258094">Gerber MA, Shulman ST (2004) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=15258094 Rapid diagnosis of pharyngitis caused by group A streptococci.] ''Clin Microbiol Rev'' 17 (3):571-80, table of contents. [http://dx.doi.org/10.1128/CMR.17.3.571-580.2004 DOI:10.1128/CMR.17.3.571-580.2004] PMID: [https://pubmed.gov/15258094 15258094]</ref>
* Can not differentiate acutely infected persons from asymptomatic streptococcal carriers with intercurrent viral pharyngitis.
| valign = top |
'''Advantages'''<br>
* High sensitivity: Culture of a single throat swab on a blood agar plate is 90%– 95% sensitive for detection of GAS pharyngitis.
'''Disadvantages'''<br>
* A major disadvantage of throat cultures is the delay (overnight or longer) in obtaining results.
* Can not differentiate acutely infected persons from asymptomatic streptococcal carriers with intercurrent viral pharyngitis.
'''Variables that affects culture results'''
*Culture methods: Use of anaerobic incubation and selective culture media may increase the proportion of positive culture results.<ref name="pmid3891893">Schwartz RH, Gerber MA, McCoy P (1985) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=3891893 Effect of atmosphere of incubation on the isolation of group A streptococci from throat cultures.] ''J Lab Clin Med'' 106 (1):88-92. PMID: [https://pubmed.gov/3891893 3891893]</ref>
* Manner in which the swab is obtained: Throat swab specimens should be obtained from the surface of either tonsils (or tonsillar fossae) and the posterior pharyngeal wall. Other areas of the oral pharynx and mouth are not acceptable sites. Uncooperative child without immobilizing the neck may obtain a specimen that is neither adequate nor representative.
* Duration of Incubation 
|}
=== '''Rapid Antigen Detection Test''' '''(RADT)''' ===
=== '''Rapid Antigen Detection Test''' '''(RADT)''' ===
RADT is useful for the identification of GAS pharyngitis directly from throat swabs. RADTs currently available are highly specific (approximately 95%) when compared with blood agar plate cultures.<ref name="pmid2687791">Gerber MA (1989) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=2687791 Comparison of throat cultures and rapid strep tests for diagnosis of streptococcal pharyngitis.] ''Pediatr Infect Dis J'' 8 (11):820-4. PMID: [https://pubmed.gov/2687791 2687791]</ref>
RADT is useful for the identification of GAS pharyngitis directly from throat swabs. RADTs currently available are highly specific (approximately 95%) when compared with blood agar plate cultures.<ref name="pmid2687791">Gerber MA (1989) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=2687791 Comparison of throat cultures and rapid strep tests for diagnosis of streptococcal pharyngitis.] ''Pediatr Infect Dis J'' 8 (11):820-4. PMID: [https://pubmed.gov/2687791 2687791]</ref>

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Venkata Sivakrishna Kumar Pulivarthi M.B.B.S [2]

Overview

Testing for pharyngitis usually is not recommended for children or adults with acute pharyngitis with clinical and epidemiological features that strongly suggest a viral etiology (eg, cough, rhinorrhea, hoarseness, and oral ulcers).[1] Diagnostic studies for GAS are not indicated for children <3 years old because acute rheumatic fever is rare in children <3 years old and the incidence of streptococcal pharyngitis and the classic presentation of streptococcal pharyngitis are uncommon in this age group. Selected children <3 years old who have other risk factors, such as an older sibling with GAS infection, may be considered for testing.[1]

Laboratory Findings

Rapid antigen detection test Throat culture

Advantages

  • Rapidity of the test: Rapid identification and treatment of patients with GAS pharyngitis can reduce the risk of spread, allowing the patient to return to school or work sooner, and can reduce the acute associated morbidity.[2]
  • High specificity: RADTs currently available are highly specific (approximately 95%) when compared with blood agar plate cultures.[3]
  • False positive test results are highly unusual, and therefore therapeutic decisions can be made with confidence on the basis of a positive test result.[4]

Disadvantages

  • Sensitivity is low: Because the sensitivities of the various RADTs are <90% and because the proportion of acute pharyngitis due to GAS in children and adolescents is sufficiently high (20%-30%), a negative RADT should be accompanied by a follow-up or back-up throat culture in children and adolescents, while this is not necessary in adults under usual circumstances.[4]
  • Can not differentiate acutely infected persons from asymptomatic streptococcal carriers with intercurrent viral pharyngitis.

Advantages

  • High sensitivity: Culture of a single throat swab on a blood agar plate is 90%– 95% sensitive for detection of GAS pharyngitis.

Disadvantages

  • A major disadvantage of throat cultures is the delay (overnight or longer) in obtaining results.
  • Can not differentiate acutely infected persons from asymptomatic streptococcal carriers with intercurrent viral pharyngitis.

Variables that affects culture results

  • Culture methods: Use of anaerobic incubation and selective culture media may increase the proportion of positive culture results.[5]
  • Manner in which the swab is obtained: Throat swab specimens should be obtained from the surface of either tonsils (or tonsillar fossae) and the posterior pharyngeal wall. Other areas of the oral pharynx and mouth are not acceptable sites. Uncooperative child without immobilizing the neck may obtain a specimen that is neither adequate nor representative.
  • Duration of Incubation

Rapid Antigen Detection Test (RADT)

RADT is useful for the identification of GAS pharyngitis directly from throat swabs. RADTs currently available are highly specific (approximately 95%) when compared with blood agar plate cultures.[3]


Viral Etiology

Bacterial Etiology

Group A streptococcus: No single element in the history or physical examination is sensitive or specific enough to exclude or diagnose strep throat.[6]

Diphtheria: The diagnosis, which may be strongly suspected on epidemiologic and clinical grounds, should be confirmed by culture of the pseudomembrane in Loeffler’s or tellurite selective medium.[7]

Neisseria gonorrhoeae: The diagnosis should be confirmed by culture on Thayer–Martin medium.[7]

Reference

  1. ↑ 1.0 1.1 Shulman ST, Bisno AL, Clegg HW, Gerber MA, Kaplan EL, Lee G et al. (2012) Clinical practice guideline for the diagnosis and management of group A streptococcal pharyngitis: 2012 update by the Infectious Diseases Society of America. Clin Infect Dis 55 (10):1279-82. DOI:10.1093/cid/cis847 PMID: 23091044
  2. ↑ Randolph MF, Gerber MA, DeMeo KK, Wright L (1985) Effect of antibiotic therapy on the clinical course of streptococcal pharyngitis. J Pediatr 106 (6):870-5. PMID: 3923180
  3. ↑ 3.0 3.1 Gerber MA (1989) Comparison of throat cultures and rapid strep tests for diagnosis of streptococcal pharyngitis. Pediatr Infect Dis J 8 (11):820-4. PMID: 2687791
  4. ↑ 4.0 4.1 Gerber MA, Shulman ST (2004) Rapid diagnosis of pharyngitis caused by group A streptococci. Clin Microbiol Rev 17 (3):571-80, table of contents. DOI:10.1128/CMR.17.3.571-580.2004 PMID: 15258094
  5. ↑ Schwartz RH, Gerber MA, McCoy P (1985) Effect of atmosphere of incubation on the isolation of group A streptococci from throat cultures. J Lab Clin Med 106 (1):88-92. PMID: 3891893
  6. ↑ Vincent MT, Celestin N, Hussain AN (2004) Pharyngitis. Am Fam Physician 69 (6):1465-70. PMID: 15053411
  7. ↑ 7.0 7.1 Bisno AL (2001) Acute pharyngitis. N Engl J Med 344 (3):205-11. DOI:10.1056/NEJM200101183440308 PMID: 11172144

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