Chlorhexidine Use Prior to Strep Throat Swab
No, chlorhexidine mouthwash should not be used prior to obtaining a throat swab for Group A Streptococcus testing, as antimicrobial agents can cause false-negative results by reducing the bacterial load on the pharyngeal surface.
Why Antimicrobial Exposure Interferes with Testing
Recent antibiotic or antimicrobial use can cause false-negative results if the patient received these agents shortly before or at the time of specimen collection 1.
Chlorhexidine is a potent antimicrobial agent that kills bacteria on contact, which would directly reduce or eliminate Group A Streptococcus organisms from the pharyngeal surface before swabbing.
Rapid antigen detection tests (RADTs) already have sensitivity limitations of 80-90% compared to throat culture, meaning they miss 10-30% of true infections even under optimal conditions 2, 1.
Adding an antimicrobial rinse before testing would further decrease the already suboptimal sensitivity, potentially converting true-positive cases to false-negatives.
Proper Specimen Collection Technique
Specimens must be obtained from both tonsillar surfaces (or tonsillar fossae) and the posterior pharyngeal wall using proper swabbing technique 1.
The swab should be collected without any prior mouth rinsing, gargling, or use of antimicrobial agents.
For optimal test performance, swabs can be collected using either a single dry Dacron swab or a swab with liquid transport media, though dry swabs may actually preserve antigen detection better over time 3.
Clinical Decision Algorithm
Calculate the Centor score (fever, tonsillar exudates, tender anterior cervical lymphadenopathy, absence of cough) to determine if testing is warranted 1.
If testing is indicated (Centor score 3-4), perform RADT on a properly collected throat swab without any prior antimicrobial exposure 1.
A positive RADT can be trusted due to ≥95% specificity and requires no culture confirmation 2, 1.
A negative RADT in children/adolescents requires backup throat culture due to the 80-90% sensitivity, while adults generally do not need confirmation 2, 1.
Common Pitfalls to Avoid
Do not allow patients to use mouthwash, gargle, or rinse their mouth before specimen collection, as this can wash away or kill the target organisms.
Do not collect specimens from patients who have already started antibiotics or used antimicrobial mouth rinses, as this significantly increases the risk of false-negative results 1.
Do not assume that using chlorhexidine will "clean" the specimen or improve test accuracy—it will only interfere with bacterial detection.