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

Research output: Contribution to journalArticle

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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
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

Ralph, Anna P. ; Holt, Deborah C. ; Islam, Sharifun ; Osowicki, Joshua ; Carroll, David E. ; Tong, Steven Y.C. ; Bowen, Asha C. / Potential for molecular testing for group a streptococcus to improve diagnosis and management in a high-risk population : A prospective study. In: Open Forum Infectious Diseases. 2019 ; Vol. 6, No. 4.
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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.",
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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.

Research output: Contribution to journalArticle

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.

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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.

KW - Group A Streptococcus

KW - molecular test

KW - pharyngotonsillitis

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