Diagnosis of bacterial infections in patient with a sore throat, or acute pharyngitis.
Indications for Testing
When there is a clinical suspicion of bacterial pharyngitis in patients with signs and/ or symptoms, including fever, sore throat, pharyngeal and tonsillar erythema, edema, and/or exudates, swollen anterior cervical nodes.
Group A Streptococcal pharyngitis is uncommon in children < 3 years old.
Repeat (post treatment) throat cultures are not routinely recommended.
Special Instructions and Forms
1. Specimens should be obtained before initiation of antimicrobial therapy.
2. E-swab is the collecting device used at the Newfoundland and Labrador Public Health and Microbiology Laboratory (PHML).
3. Specimens should be obtained by vigorous swabbing of both tonsils (and tonsillar fossae in patients who have undergone tonsillectomy) and the posterior pharynx.
4. The swab(s) should be moved into and out of the mouth without touching the tongue or the buccal mucosa.
5. Write down name, date and time of collection.
Sample should be sent to the lab for testing as soon as possible.
Submit specimen using the Public Health and Microbiology Specimen Collection Requisition
1. Throat culture
1. Throat culture
Aliases (clinical indications)
Group A streptococcus
Throat swabs in E-Swab transport media.
Specimen Minimum Volume
|E-swab of Tonsils, tonsillar fossa, or posterior pharynx||48 hours||Not recommended|
Reject Due To
|Incorrect swabs||The lab will reject specimen in all other swabs than the E-swabs. Recollection recommended.|
|Delayed in arriving the lab for testing||Recollection recommended if clinically indicated.|
|Repeat specimens||Repeat submission would be rejected without clinical justification.|
⃰ Rejected samples would be kept for 5 days. However it would NOT be suitable for setting up to bacterial workup after 48 hours post-collection.
Even though the majority of cases of pharyngitis are of viral etiology, clinical signs and symptoms are not specific to distinguish between bacterial and viral pharyngitis. The diagnosis must be made by throat culture. Generally, throat cultures do NOT need to be done when viral infection is suspected by the presence of: rhinorrhea, hoarseness, cough, and conjunctivitis.
Group A Streptococcus (GAS, S. pyogenes) is the most commonly encountered bacterial pathogen in pharyngitis. Other bacterial causes include other beta-haemolytic streptococci (group C and G), Neisseria gonorrhoeae and Arcanobacterium haemolyticum. Antibiotic therapy to confirmed Group A Streptococcal Pharyngitis can decrease the risk of transmission (after 24 hours of therapy) and the likelihood of supporative complications and rheumatic fever. The clinical significance and treatment of Group C and G streptococcus remains controversial.
Identification of GAS causing acute bacterial pharyngitis.
Throat culture will be set up per the laboratory standard operational procedure (SOP). Only GAS (S. pyogenes) is to be identified and reported.
Antimicrobial susceptibility testing is NOT routinely performed because isolates resistant to penicillins and other β-lactams have not been reported for S. pyogenes. Penicillin and ampicillin are the drugs of choice for treatment of Group A streptococcal infections. For patient with severe anaphylactic allergy to penicillin, the isolated group A Streptococcus may be set up for susceptibility testing upon special request.
- No significant growth
- Throat culture has up to 95% sensitivity in appropriately collected specimens. However, a positive throat culture may reflect chronic colonization by GAS.
- The test will report only the Group A Streptococcus (GAS) result.
Garcia Lynne S., ed. Clinical Microbiology Procedures Handbook. 3rd ed. Washington, ASM Press, 2010
Test Frequency and Turnaround Time (TAT)
Throat culture is a routine test performed daily, Monday to Sunday.
Turnaround time is up to 5 days from receipt by PHML laboratory.
Routine bacterial culture.