Can you test for strep too early

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Can You Test for Strep Too Early?

Testing for streptococcal infections, particularly Group A Streptococcus (GAS) and Group B Streptococcus (GBS), is crucial for timely diagnosis and treatment. However, the timing of these tests can significantly impact their accuracy and utility. This article explores whether testing for strep can be done too early, based on recent research findings.

Rapid Identification Methods for Streptococci

Rapid ID 32 Strep System

The Rapid ID 32 Strep system is designed to identify most streptococci and related genera within 4 hours. This system has shown a high accuracy rate, correctly identifying 95.3% of the strains tested. However, 25.1% of these cases required additional tests for complete identification, and a small percentage were either not identified or misidentified . This suggests that while rapid identification is possible, it may not always be definitive without supplementary testing.

Alere i Strep A Test

The Alere i Strep A test is another rapid diagnostic tool, specifically for GAS. It offers highly sensitive results within 8 minutes and can be performed by non-laboratory personnel. In a multicenter trial, this test demonstrated a sensitivity of 96.0% and a specificity of 94.6% compared to bacterial culture. When discrepancies were resolved using PCR, the sensitivity and specificity increased to 98.7% and 98.5%, respectively . This high level of accuracy makes it a reliable option for point-of-care testing, reducing the need for backup testing.

Timing of GBS Testing

Rapid PCR vs. Standard Culture

For GBS, the timing of testing is particularly critical. A study comparing a rapid PCR test (IDI-Strep B) performed during labor with the standard culture test done at 35 to 37 weeks' gestation found that the rapid PCR had higher sensitivity (90.7%) and specificity (97.6%) compared to the standard screen (84.3% sensitivity and 93.2% specificity) . The rapid PCR test provided results within a median time of 99 minutes, which was sufficiently quick to allow for timely administration of intrapartum prophylactic antibiotics in most cases.

Conclusion

In summary, while rapid testing methods for streptococcal infections are highly effective, the timing of these tests is crucial. For GAS, rapid tests like the Alere i Strep A offer quick and reliable results, making them suitable for point-of-care use. For GBS, rapid PCR testing during labor provides more accurate and timely results compared to standard culture tests done weeks earlier. Therefore, while it is possible to test for strep too early, advancements in rapid testing technology are mitigating these concerns, ensuring timely and accurate diagnosis and treatment.

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Most relevant research papers on this topic

Description and evaluation of the semiautomated 4-hour rapid ID 32 Strep method for identification of streptococci and members of related genera

The rapid ID 32 Strep system effectively identifies 95.39% of streptococci and related genera in 4 hours, offering a suitable alternative for rapid identification in medical and veterinary bacteriology.

Highly Cited

1992·

81citations

·J. Freney et al.

An evaluation of a rapid real time polymerase chain reaction assay for detection of group B streptococcus as part of a neonatal group B streptococcus prevention strategy.

Rapid PCR test during labor (IDI-Strep B) demonstrated high sensitivity and specificity, comparable to the 35- to 37-week screen, with acceptable short reporting time for timely administration of intrapartum prophylactic antibiotics.

Observational Study

2008·

43citations

·D. Money et al.

Multicenter Clinical Evaluation of the Novel Alere i Strep A Isothermal Nucleic Acid Amplification Test

The Alere i strep A test offers highly sensitive, point-of-care results for group A beta-hemolytic streptococcus pharyngitis, eliminating the need for backup testing and reducing costs.

Observational StudyRigorous Journal

2015·

57citations

·D. Cohen et al.

Evaluation of Detect-A-Strep and the Culturette Ten-Minute Strep ID kits for detection of group A streptococcal antigen in oropharyngeal swabs from children

Both Detect-A-Strep and Culturette 10-Minute Group A Strep ID kits are not sufficiently sensitive to replace our culture method for detecting group A streptococci in oropharyngeal swabs from children.

In Vitro Study

1985·

37citations

·J. Campos et al.

Multicenter Clinical Evaluation of the Revogene Strep A Molecular Assay for Detection of Streptococcus pyogenes from Throat Swab Specimens

The Revogene Strep A molecular assay provides high sensitivity and specificity for detecting Group A streptococcus from throat swab specimens, offering a faster alternative for GAS diagnosis.

Observational StudyRigorous Journal

2020·

9citations

·D. Banerjee et al.

Evaluation of the Strep-A-Chek technique for presumptive identification of group A beta-hemolytic streptococci and group D enterococci.

Strep-A-Chek is a rapid and reliable test for presumptive identification of group A and enterococcal streptococci, saving 24 hours compared to conventional methods.

1987·

7citations

·J. Daly et al.

Comparison of direct specimen testing utilizing TestPack strep A with testing of specimens following a two-hour broth enrichment.

A two-hour broth enrichment method using enzyme immunoassay offers significantly greater sensitivity than direct testing for group-A streptococci, with potential for same-day reporting of results.

1993·

12citations

·P. Bourbeau et al.

Accurate Detection of Streptococcus pyogenes at the Point of Care Using the cobas Liat Strep A Nucleic Acid Test

The cobas Liat Strep A assay provides accurate, point-of-care detection of group A Streptococcus bacteria in primary care settings, with comparable sensitivity and specificity to culture, and a 15-minute turnaround time compared to rapid antigen detection tests.

Observational Study

2017·

40citations

·Fangnian Wang et al.

Use of the Rapid STREP system for identification of viridans streptococcal species

The Rapid STREP system is a fairly accurate and rapid method for identifying viridans streptococcal species, with 92% correct identifications and 81% of correct identifications at 90 or greater.

1983·

28citations

·K. Ruoff et al.

Performance and Practicality of a Rapid Molecular Test for the Diagnosis of Strep A Pharyngitis in a Remote Australian Setting.

Rapid molecular testing effectively identified Strep A pharyngitis in remote Australian schoolchildren, making it highly practical for remote settings.

Observational StudyRigorous Journal

2020·

13citations

·Janessa L. Pickering et al.

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