Role of investigations in viral and streptococcal pharyngitis and tonsillitis

Throat swab culture can detect S. pyogenes; however, S. pyogenes can colonise the throat and a positive culture result does not distinguish between true S. pyogenes pharyngitis or tonsillitis and S. pyogenes carriers with pharyngitis or tonsillitis caused by a viral pathogenOliver, 2018. Determining if a patient is at high risk of acute rheumatic fever is an important consideration when assessing the need for a throat swab culture:

• patients at high risk of acute rheumatic fever—a throat swab for culture is useful to provide evidence of preceding S. pyogenes infection if the patient is later suspected to have acute rheumatic fever. If possible, collect a throat swab before starting antibiotic therapy
• patients not at high risk of acute rheumatic fever—a throat swab for culture is not routinely recommended, but is useful if antibiotic therapy is being considered.

Rapid tests for diagnosis of S. pyogenes infection (eg rapid antigen test, nucleic acid amplification test) are not easily accessible in Australia, and are not currently widely used.

Nucleic acid amplification testing (eg polymerase chain reaction [PCR]) to detect respiratory viruses can be used to increase confidence in the diagnosis of a viral infection and support not prescribing antibiotics for pharyngitis and tonsillitis in patients not at high risk of acute rheumatic fever. A negative nucleic acid amplification test result may not exclude viral infection, depending on the breadth of the testing panel and the quality of the sample.

In all patients presenting with a sore throat, refer to state and territory health department guidelines for advice on testing for severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2).