From the Guidelines
A throat swab for strep throat may still be positive after 3 days of amoxicillin treatment, though results can vary between patients. While amoxicillin typically begins killing Streptococcus pyogenes bacteria within 24 hours, complete eradication from the throat can take longer. Patients are generally considered non-contagious after 24-48 hours of appropriate antibiotic therapy, but bacterial DNA can remain detectable by testing for several days or even weeks after starting treatment. This persistence doesn't necessarily indicate active infection or contagiousness. For accurate diagnostic testing, it's ideal to obtain a throat swab before starting antibiotics. If a patient has already begun treatment and testing is needed, this timing should be noted when interpreting results. Regardless of test results, patients should complete the full prescribed course of antibiotics (typically 10 days for amoxicillin) to ensure complete eradication of the bacteria and prevent complications like rheumatic fever, as recommended by the Infectious Diseases Society of America 1. Some key points to consider in the management of strep throat include:
- The choice of antibiotic, such as amoxicillin, and its dosage, which should be based on the patient's weight and medical history 1.
- The importance of completing the full course of antibiotics to prevent complications, as emphasized in the guidelines for the diagnosis and management of group A streptococcal pharyngitis 1.
- The potential for bacterial DNA to remain detectable after starting treatment, which should be taken into account when interpreting test results 1. It is essential to follow the recommended treatment guidelines to ensure the best possible outcomes for patients with strep throat, in terms of morbidity, mortality, and quality of life.
From the Research
Throat Swab Results After Amoxicillin Treatment
- A study from 1993 2 found that after 2 days of amoxicillin treatment, 4% of patients still had positive throat cultures, while after 14 days, no positive cultures were observed.
- Another study from 2015 3 reported that 12-23 hours after a single dose of amoxicillin, 91% of participants had negative throat swab results, confirmed by overnight throat culture.
- However, it is essential to note that the duration of amoxicillin treatment in the question is 3 days, which is longer than the treatment duration in the 2015 study 3.
- A 2021 review 4 recommends treating children with amoxicillin or penicillin when a throat swab is positive for Group A Streptococcus (GAS), but does not provide specific information on the timing of throat swab results after treatment.
- A 2009 article 5 states that penicillin or amoxicillin is the treatment of choice for streptococcal pharyngitis, but does not provide information on the expected timing of negative throat swab results after treatment.
- A 2020 review 6 discusses the diagnostic methods and treatment guidelines for Group A Streptococcal Pharyngitis, but does not provide specific information on the expected timing of negative throat swab results after amoxicillin treatment.
Expected Throat Swab Results
- Based on the available evidence, it is likely that a throat swab will be negative after 3 days of amoxicillin treatment, but the exact timing of negative results may vary depending on individual factors.
- The 2015 study 3 suggests that a significant proportion of patients may have negative throat swab results within 12-23 hours of starting amoxicillin treatment, which supports the possibility of negative results after 3 days of treatment.