Throat swab

A throat swab is a microbiological test that cultures the bacterium causing inflammation from a sample of the pharyngeal and tonsillar mucosa. It is most often performed when streptococcal throat infection (strep throat) is suspected, because the result determines whether an antibiotic is needed.

Who the test is for

• people with a sore throat accompanied by fever, swollen and tender lymph nodes in the neck, and red, swollen tonsils with pus deposits,
• people with a sore throat without cough, runny nose, hoarseness or mouth sores,
• people whose sore throat recurs or does not go away,
• children under three years of age only if someone in the family has confirmed strep throat, since it is rare at that age.

What a throat swab shows

Most throat infections are caused by viruses, against which antibiotics do not work. The most important bacterial cause is group A beta-haemolytic streptococcus (Streptococcus pyogenes), while group C and G streptococci cause pharyngitis less often. Strep throat is most common in school-age children and spreads easily in nurseries, schools and families through droplets and close contact, but also occurs in adults.

The sample is inoculated onto culture media. If a bacterium capable of causing pharyngitis grows, the report states its name and, when necessary, an antibiogram, meaning a list of antibiotics to which the bacterium is susceptible.

A throat swab does not detect viruses. Bacteria in a swab do not always mean disease either: some healthy children and adults carry streptococci in their throat without any symptoms (carriers).

A doctor recommends a throat swab for a sore throat suggestive of bacterial infection. Cough, runny nose, hoarseness and mouth sores are more suggestive of a virus.

If your sore throat is accompanied by difficulty swallowing saliva or breathing, inability to open your mouth, or pronounced swelling on one side only, seek a doctor or emergency department immediately.

Preparation and sample

• The swab is best taken before starting antibiotic treatment, because antibiotics can produce a false-negative result. If you have already taken an antibiotic, mention this when the sample is taken.
• Come in the morning, before eating or drinking and before brushing your teeth. If you come later in the day, do not eat, drink, brush your teeth or use lozenges, throat sprays or mouthwash for at least 2 hours beforehand.
• A spatula is used to gently depress the tongue while a sterile cotton swab is passed over the tonsils and back of the throat. Sampling takes a few seconds and is painless, but may briefly trigger the gag reflex.

How to interpret the result

A negative result, often described as usual or normal flora, means that no bacteria causing pharyngitis grew. The sore throat is then most often viral and resolves on its own with rest, fluids and painkillers.

A positive result states the pathogen and, if necessary, an antibiogram. Your doctor decides on treatment based on the result and symptoms, because streptococci in the throat of a person without symptoms do not always require an antibiotic. In strep throat, an antibiotic shortens the illness and prevents rare but serious complications, such as a pus-filled abscess beside the tonsil and rheumatic fever. Group A streptococcus is generally susceptible to penicillin, and an antibiogram is particularly important in people allergic to penicillin.

How to arrange testing

A nurse takes throat swabs at all our branches, without an appointment or referral (branch list on the page Contact). Prices for all tests and panels are available in the service price list.

Frequently asked questions

What is the difference between a throat swab and a rapid strep test?

A rapid antigen test on a throat swab detects only group A streptococcus and does not require bacterial culture. A throat swab with culture also detects other bacterial causes and allows an antibiogram. In children and adolescents, a doctor usually confirms a negative rapid test with a throat swab culture, whereas in adults this is generally unnecessary.

Is a nasal swab also needed alongside a throat swab?

A throat swab is sufficient for strep throat. A nasal swab is performed when a doctor is looking for a pathogen in the nose, for example in recurrent purulent infections or to check for Staphylococcus aureus carriage. If your doctor requests both, they can be taken during the same visit.

Is a follow-up swab needed after antibiotics?

If the symptoms have resolved, a follow-up swab is generally unnecessary. Your doctor may request one if symptoms return or in special circumstances.

Can a throat swab detect mononucleosis?

No. Infectious mononucleosis is caused by a virus and can look very similar to strep throat. It is detected through blood tests, so a doctor requests a blood count and antibodies when it is suspected.