Potential for molecular testing for group a streptococcus to improve diagnosis and management in a high-risk population

A prospective study

Anna P. Ralph, Deborah C. Holt, Sharifun Islam, Joshua Osowicki, David E. Carroll, Steven Y.C. Tong, Asha C. Bowen

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    Abstract

    Background: In high-burden settings, guidelines recommend antibiotic treatment for all suspected group A Streptococcus (GAS) infections to prevent rheumatic fever and poststreptococcal glomerulonephritis. Highly sensitive rapid GAS tests could reduce unnecessary antibiotic use in these settings.

    Methods: This was a prospective study of the Xpert Xpress Strep A (Cepheid) molecular test compared with culture of throat swab samples collected at a referral hospital in northern Australia. Demographic and clinical data and results of streptococcal serology and culture were collected.

    Results: Of 164 throat swab samples, 145 (88%) were eligible for inclusion; 49 (34%) were molecular test positive and 24 (17%) were culture positive for GAS. The sensitivity, specificity, and positive and negative predictive values for the molecular test versus culture were 100.0%, 79.3%, 48.8%, and 100.0%, respectively. Among 25 samples testing positive with the molecular test and negative with culture, group C or G streptococci were cultured in 2, and a plausible clinical explanation, such as pharyngotonsillitis, or rheumatic fever with positive results of streptococcal serology, was apparent in 19 instances. In 25 patients with rheumatic fever or poststreptococcal glomerulonephritis diagnoses, molecular testing nearly trebled the detection of GAS in throat swab samples, from 3 (12%) detected with culture to 8 (32%) detected with molecular testing. Reasons for "false-positive" molecular test results could include the presence of GAS below the threshold of culture detection or persistence of nonviable organisms after infection.

    Conclusion: Implementation of molecular testing could improve antibiotic use in this high-burden setting. The incremental yield in poststreptococcal syndromes, by which time cultures are negative, has high potential in the diagnostic workup of autoimmune poststreptococcal syndromes and warrants further investigation.

    Original languageEnglish
    Article numberofz097
    Pages (from-to)1-9
    Number of pages9
    JournalOpen Forum Infectious Diseases
    Volume6
    Issue number4
    DOIs
    Publication statusPublished - 1 Apr 2019

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    Streptococcus
    Prospective Studies
    Rheumatic Fever
    Pharynx
    Population
    Serology
    Glomerulonephritis
    Anti-Bacterial Agents
    Predictive Value of Tests
    Infection
    Referral and Consultation
    Demography
    Guidelines
    Sensitivity and Specificity

    Cite this

    @article{a3b13ba8f2eb4419ab15c509f819b19a,
    title = "Potential for molecular testing for group a streptococcus to improve diagnosis and management in a high-risk population: A prospective study",
    abstract = "Background: In high-burden settings, guidelines recommend antibiotic treatment for all suspected group A Streptococcus (GAS) infections to prevent rheumatic fever and poststreptococcal glomerulonephritis. Highly sensitive rapid GAS tests could reduce unnecessary antibiotic use in these settings. Methods: This was a prospective study of the Xpert Xpress Strep A (Cepheid) molecular test compared with culture of throat swab samples collected at a referral hospital in northern Australia. Demographic and clinical data and results of streptococcal serology and culture were collected. Results: Of 164 throat swab samples, 145 (88{\%}) were eligible for inclusion; 49 (34{\%}) were molecular test positive and 24 (17{\%}) were culture positive for GAS. The sensitivity, specificity, and positive and negative predictive values for the molecular test versus culture were 100.0{\%}, 79.3{\%}, 48.8{\%}, and 100.0{\%}, respectively. Among 25 samples testing positive with the molecular test and negative with culture, group C or G streptococci were cultured in 2, and a plausible clinical explanation, such as pharyngotonsillitis, or rheumatic fever with positive results of streptococcal serology, was apparent in 19 instances. In 25 patients with rheumatic fever or poststreptococcal glomerulonephritis diagnoses, molecular testing nearly trebled the detection of GAS in throat swab samples, from 3 (12{\%}) detected with culture to 8 (32{\%}) detected with molecular testing. Reasons for {"}false-positive{"} molecular test results could include the presence of GAS below the threshold of culture detection or persistence of nonviable organisms after infection. Conclusion: Implementation of molecular testing could improve antibiotic use in this high-burden setting. The incremental yield in poststreptococcal syndromes, by which time cultures are negative, has high potential in the diagnostic workup of autoimmune poststreptococcal syndromes and warrants further investigation.",
    keywords = "Group A Streptococcus, molecular test, pharyngotonsillitis, point-of-care test, rheumatic fever",
    author = "Ralph, {Anna P.} and Holt, {Deborah C.} and Sharifun Islam and Joshua Osowicki and Carroll, {David E.} and Tong, {Steven Y.C.} and Bowen, {Asha C.}",
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    Potential for molecular testing for group a streptococcus to improve diagnosis and management in a high-risk population : A prospective study. / Ralph, Anna P.; Holt, Deborah C.; Islam, Sharifun; Osowicki, Joshua; Carroll, David E.; Tong, Steven Y.C.; Bowen, Asha C.

    In: Open Forum Infectious Diseases, Vol. 6, No. 4, ofz097, 01.04.2019, p. 1-9.

    Research output: Contribution to journalArticleResearchpeer-review

    TY - JOUR

    T1 - Potential for molecular testing for group a streptococcus to improve diagnosis and management in a high-risk population

    T2 - A prospective study

    AU - Ralph, Anna P.

    AU - Holt, Deborah C.

    AU - Islam, Sharifun

    AU - Osowicki, Joshua

    AU - Carroll, David E.

    AU - Tong, Steven Y.C.

    AU - Bowen, Asha C.

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    N2 - Background: In high-burden settings, guidelines recommend antibiotic treatment for all suspected group A Streptococcus (GAS) infections to prevent rheumatic fever and poststreptococcal glomerulonephritis. Highly sensitive rapid GAS tests could reduce unnecessary antibiotic use in these settings. Methods: This was a prospective study of the Xpert Xpress Strep A (Cepheid) molecular test compared with culture of throat swab samples collected at a referral hospital in northern Australia. Demographic and clinical data and results of streptococcal serology and culture were collected. Results: Of 164 throat swab samples, 145 (88%) were eligible for inclusion; 49 (34%) were molecular test positive and 24 (17%) were culture positive for GAS. The sensitivity, specificity, and positive and negative predictive values for the molecular test versus culture were 100.0%, 79.3%, 48.8%, and 100.0%, respectively. Among 25 samples testing positive with the molecular test and negative with culture, group C or G streptococci were cultured in 2, and a plausible clinical explanation, such as pharyngotonsillitis, or rheumatic fever with positive results of streptococcal serology, was apparent in 19 instances. In 25 patients with rheumatic fever or poststreptococcal glomerulonephritis diagnoses, molecular testing nearly trebled the detection of GAS in throat swab samples, from 3 (12%) detected with culture to 8 (32%) detected with molecular testing. Reasons for "false-positive" molecular test results could include the presence of GAS below the threshold of culture detection or persistence of nonviable organisms after infection. Conclusion: Implementation of molecular testing could improve antibiotic use in this high-burden setting. The incremental yield in poststreptococcal syndromes, by which time cultures are negative, has high potential in the diagnostic workup of autoimmune poststreptococcal syndromes and warrants further investigation.

    AB - Background: In high-burden settings, guidelines recommend antibiotic treatment for all suspected group A Streptococcus (GAS) infections to prevent rheumatic fever and poststreptococcal glomerulonephritis. Highly sensitive rapid GAS tests could reduce unnecessary antibiotic use in these settings. Methods: This was a prospective study of the Xpert Xpress Strep A (Cepheid) molecular test compared with culture of throat swab samples collected at a referral hospital in northern Australia. Demographic and clinical data and results of streptococcal serology and culture were collected. Results: Of 164 throat swab samples, 145 (88%) were eligible for inclusion; 49 (34%) were molecular test positive and 24 (17%) were culture positive for GAS. The sensitivity, specificity, and positive and negative predictive values for the molecular test versus culture were 100.0%, 79.3%, 48.8%, and 100.0%, respectively. Among 25 samples testing positive with the molecular test and negative with culture, group C or G streptococci were cultured in 2, and a plausible clinical explanation, such as pharyngotonsillitis, or rheumatic fever with positive results of streptococcal serology, was apparent in 19 instances. In 25 patients with rheumatic fever or poststreptococcal glomerulonephritis diagnoses, molecular testing nearly trebled the detection of GAS in throat swab samples, from 3 (12%) detected with culture to 8 (32%) detected with molecular testing. Reasons for "false-positive" molecular test results could include the presence of GAS below the threshold of culture detection or persistence of nonviable organisms after infection. Conclusion: Implementation of molecular testing could improve antibiotic use in this high-burden setting. The incremental yield in poststreptococcal syndromes, by which time cultures are negative, has high potential in the diagnostic workup of autoimmune poststreptococcal syndromes and warrants further investigation.

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    KW - molecular test

    KW - pharyngotonsillitis

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