Throat swab

Specimen:

Swab rotated on area of inflammation and placed in transport medium for bacterial culture.

If diphtheria or gonorrhoea is suspected special testing should be requested.

If viral detection is indicated a separate swab in viral transport medium is required. Laboratories performing nucleic acid detection after amplification may prefer a dry swab.

A swab in viral transport medium is required for culture.

See also Influenza Ab and Influenza Ag.

Method:

Culture for ß-haemolytic streptococci and other bacteria (if appropriate).

Gram stain for microscopy only if Vincent’s angina is suspected.

Viral, mycoplasma and chlamydial cultures are seldom performed and only on special request in appropriate clinical circumstances.

Special stains, culture and toxin detection are required for the identification of Corynebacterium diphtheriae.

Virus detection, culture.

Application:

Used to establish the diagnosis of bacterial infection with ß-haemolytic streptococci (especially Group A (Streptococcus pyogenes), Group C or Group G) and Arcanobacterium haemolyticum.

A throat swab is required to diagnose suspected Vincent’s angina and gonococcal pharyngitis or herpes simplex infection and to confirm a clinical diagnosis of diphtheria.

Viral detection culture to determine viral aetiology of meningitis or encephalitis.

Viral detection culture is seldom indicated to determine other viral causes of pharyngitis, but can be used to establish a diagnosis of influenza. Influenza Ag gives a more rapid result.

Interpretation:

The culture of a significant growth of ß-haemolytic streptococci, Group A or G, in the presence of clinical pharyngitis confirms their pathogenic role.

Absence of significant bacterial isolates makes a viral cause (eg, adenovirus, rhinovirus, influenza A or B, coronavirus) most likely.

Arcanobacterium (Corynebacterium) haemolyticum, Corynebacterium diphtheriae, Neisseria gonorrhoeae, Mycoplasma spp and Chlamydia spp are much less common causes of pharyngitis.

In suspected Vincent’s angina, Gram stain of a swab from the affected area will have a characteristic appearance.

Reference:

Del Mar C. Med J Aust 1992; 156: 572-575.