Scarlet Fever and Streptococcal Pharyngitis
On this page
Direct answer
Scarlet fever is a rash that accompanies Group A streptococcal pharyngitis, caused by Streptococcus pyogenes releasing erythrogenic toxins. It presents with sore throat, fever, a fine sandpaper-like rash starting on the neck and chest, and a strawberry tongue. Ten days of penicillin eradicates the streptococcus and prevents rheumatic fever.
What you must remember
- Organism: Streptococcus pyogenes, the Group A beta-haemolytic streptococcus.
- Toxins: erythrogenic toxins released by the bacterium produce the characteristic rash.
- Rash: fine, sandpaper-like erythema that starts on the neck and chest and spreads, with circumoral pallor.
- Pastia lines: linear petechial markings in skin folds such as the antecubital fossa and axilla.
- Tongue: a white strawberry coat in the early days, which later peels to a red strawberry tongue.
- Diagnosis: rapid antigen detection test from a throat swab, with throat culture when a child with high suspicion has a negative test.
- Treatment: penicillin for ten days, or a single dose of benzathine penicillin where adherence is doubtful.
- Complications: rheumatic fever and acute post-streptococcal glomerulonephritis, with desquamation of the fingers in convalescence.
From a sore throat with a rash to a confirmed diagnosis
A 7-year-old has had sore throat, fever and a rash on the neck for two days. The steps below confirm Group A streptococcal infection and prevent its late complications.
- Examine the throat: look for tonsillar exudate, tender anterior cervical nodes and petechiae on the palate.
- Look at the rash and tongue: note the sandpaper rash, circumoral pallor, Pastia lines and the strawberry tongue.
- Run a rapid antigen test: a positive result confirms Group A streptococcus, while a negative result in a high-suspicion child needs throat culture.
- Start penicillin: give oral penicillin for ten days, or a single dose of benzathine penicillin when adherence is doubtful.
- Keep the child at home: the child stays away from school until fever settles and at least 24 hours have passed since antibiotics began.
- Watch for late complications: rheumatic fever appears two to four weeks after untreated pharyngitis, and glomerulonephritis follows after a latent period.
Where the exam tries to catch you
Questions on this topic test the rash signs, the diagnostic test and the complications.
- Trap: assuming the rash means measles or a viral illness and withholding antibiotics Correct: a sore throat with a rash and a positive rapid antigen test is Group A streptococcal infection, which needs penicillin.
- Trap: choosing a macrolide as first line without a reason Correct: penicillin remains first line, and macrolides are reserved for children with penicillin allergy.
- Trap: seeing a strawberry tongue and diagnosing Kawasaki disease Correct: strawberry tongue also occurs in scarlet fever, so the other Kawasaki features must be sought.
- Trap: believing rheumatic fever follows impetigo Correct: rheumatic fever follows pharyngitis, whereas glomerulonephritis can follow either pharyngeal or skin infection.
Frequently asked questions
What causes scarlet fever?
Scarlet fever is caused by Group A streptococcus, Streptococcus pyogenes, infecting the throat or skin. Erythrogenic toxins produced by the bacterium cause the characteristic rash. Scarlet fever is best understood as a manifestation of streptococcal pharyngitis.
What is the rapid antigen test used for in scarlet fever?
The rapid antigen detection test identifies Group A streptococcus from a throat swab within minutes. A positive result confirms the diagnosis and supports antibiotic treatment. A negative result in a child with high suspicion should be followed by a throat culture.
What are Pastia lines in scarlet fever?
Pastia lines are linear, deep-red or petechial markings in skin folds, such as the antecubital fossa, axilla and groin. They appear during the rash of scarlet fever. Their presence helps a clinician recognise the scarlet fever rash on examination.
What are the complications of untreated streptococcal pharyngitis?
Untreated Group A streptococcal pharyngitis can lead to rheumatic fever, which typically appears two to four weeks after the sore throat. Rheumatic heart disease is a major concern in India. Acute post-streptococcal glomerulonephritis is another complication, following the infection after a latent period.
What is the treatment of choice for streptococcal pharyngitis and scarlet fever?
Penicillin is the treatment of choice for streptococcal pharyngitis and scarlet fever. Oral penicillin is given for ten days, or a single dose of benzathine penicillin is used when adherence is doubtful. Macrolides are reserved for children with penicillin allergy.