What is the difference between a throat culture and a streptococcal (strep) culture?

From the Guidelines

A throat culture and a strep culture are essentially the same test when looking for strep throat, though they differ in specificity and timing, with the most recent guidelines from 2013 1 supporting the use of rapid antigen detection tests and/or culture of a throat swab for diagnosis. When a patient presents with sore throat symptoms, the standard approach is to first perform a rapid strep test, which provides results in minutes but has lower sensitivity, while a traditional throat culture takes 24-48 hours but is more accurate for detecting Group A Streptococcus.

• The sensitivity of rapid strep tests is between 80% and 90%, or even lower, compared with blood agar plate culture 1.
• The specificity of most rapid strep tests is excellent, at 95% or higher, compared with blood agar plate culture 1.
• If the rapid test is positive, treatment with antibiotics like penicillin V (250-500mg orally twice daily for 10 days), amoxicillin (500mg twice daily for 10 days), or azithromycin (500mg on day 1, then 250mg daily for 4 more days) for penicillin-allergic patients can begin immediately.
• If the rapid test is negative but clinical suspicion remains high, a backup throat culture should be collected and the patient followed up when results return, as recommended by the 2013 guidelines 1. This two-step approach balances the need for quick treatment decisions with diagnostic accuracy, and is supported by the most recent and highest quality evidence 1.
• The distinction between throat culture and strep culture matters because proper identification of strep throat allows for appropriate antibiotic treatment, which prevents complications like rheumatic fever and reduces symptom duration and contagiousness.
• The use of rapid antigen detection tests and/or culture of a throat swab for diagnosis is recommended by the Infectious Diseases Society of America 1, and is supported by the most recent guidelines from 2013 1.

From the Research

Difference between Throat Culture and Strep Culture

• A throat culture is a test used to identify the presence of bacteria in the throat, whereas a streptococcal (strep) culture is a specific test used to detect the presence of group A beta-hemolytic streptococci (GABHS) in the throat 2.
• Throat culture alone is sufficient for most patients, and all negative rapid tests should be confirmed by throat culture 2.
• Strep culture is used to confirm the diagnosis of streptococcal pharyngitis, which is a bacterial infection caused by GABHS 3, 4.
• The sensitivity and specificity of rapid antigen detection tests for streptococcal pharyngitis vary, with sensitivity ranging from 81.0-96.0% and specificity ranging from 70.6-84.9% 5.
• Throat culture is considered the gold standard for diagnosing streptococcal pharyngitis, and rapid antigen detection tests should be used in conjunction with throat culture to confirm the diagnosis 2, 5.

Key Points

• Throat culture is a broader test that can detect various types of bacteria in the throat.
• Strep culture is a specific test used to detect GABHS, the bacteria that cause streptococcal pharyngitis.
• Rapid antigen detection tests can be used to quickly diagnose streptococcal pharyngitis, but should be confirmed by throat culture due to the risk of false positives and negatives 6, 5.
• The choice of test depends on the clinical presentation and the need for rapid diagnosis and treatment 2, 3, 4.