A 40-year-old woman, with no relevant past medical history presented with a 12-h history of generalized febrile rash along with intense pruritus, which began on the neck with subsequent extension to the trunk and limbs. She reported high fever, arthralgia, and odynophagia of two days’ duration, for which she had taken an oral analgesic that she had previously used in the past. The patient was a schoolteacher and reported several cases of tonsillitis at her workplace in recent weeks.

A diffuse desquamative maculopapular exanthem was observed, without palmoplantar involvement. It had a rough texture on palpation and was accompanied by a fine whitish desquamation (Fig. 1). Examination of the fauces revealed a coated tongue, as well as hyperemic tonsils with whitish exudate. Painful cervical lymphadenopathy was also present.

Fig. 1

A rapid detection test for Streptococcus pyogenes was performed, which tested positive. Laboratory analysis showed mild leukocytosis predominantly due to neutrophils, with a C-reactive protein level of 209.0mg/L, without associated renal impairment in blood or urine tests. Serology was compatible with a past infection with Epstein–Barr virus.

What is your diagnosis?

Scarlet fever.

A dose of 1.2 million IU of intramuscular benzathine penicillin G was administered, and an oral antihistamine was prescribed for symptomatic relief. The patient showed improvement of the skin lesions and pharyngeal discomfort within 12h, with complete resolution after 3 days.

Scarlet fever – scarlatina, anginous scarlet fever – is an infectious disease mediated by the erythrogenic exotoxins SpeA, SpeB, and SpeC of group A streptococcus (GAS). Classically, it has been included among the pediatric exanthems, given that up to 80% of the population acquires antitoxin after the first GAS infection at around 10 years of age.1,2 Adult involvement is uncommon, accounting for <5%.2

In December 2022, the World Health Organization (WHO) issued an alert regarding an increase in scarlet fever cases in five European countries: the United Kingdom (UK), France, Netherlands, and Sweden.3 In the UK, 4622 cases of scarlet fever were reported, exceeding the incidence of 1,92 cases recorded over the previous 5 years. Up to 5% of cases occurred in adults.4 The WHO considers immunocompromised adult populations to be at risk, and the US Centers for Disease Control and Prevention include occupations involving contact with large groups (daycare centers, schools, military bases).5 Additionally, cases of foodborne transmission have been reported, as well as cases following pelvic infections, burns, or wounds (surgical scarlet fever).2

Typical of the spring and autumn months, scarlet fever usually presents as exudative pharyngitis with high fever and painful cervical lymphadenopathy, followed by a rash that appears 12–48h later on the neck, axillae, or trunk, with subsequent generalization. The exanthem has a characteristic sandpaper-like texture. Petechiae are not uncommon, manifesting as linear streaks in flexural regions (Pastia lines) or as enanthem on the palate. The tongue may show an edematous appearance that varies according to the stage of development: initially covered by a whitish coating (coated phase), which when shed reveals diffuse erythema with hyperplastic papillae (strawberry phase). Diagnosis is clinical, although it may be supported by rapid detection tests and, in cases of negativity but high clinical suspicion, by throat culture to demonstrate the presence of GAS.1,2 It must be differentiated from other causes of febrile exanthem, such as drug eruptions, viral exanthems, infection by Arcanobacterium haemolyticum, streptococcal toxic shock syndrome (STSS), Kawasaki disease, recurrent perineal erythema, and other classical causes of exanthems in childhood as well as adulthood.

Scarlet fever requires appropriate treatment due to the risk of complications (suppurative and non-suppurative), as well as progression to STSS. Most occur early, although late complications (rheumatic fever, arthritis, and glomerulonephritis) manifest 2–3 weeks after the initial diagnosis. Regimens with penicillin or its derivatives are recommended. Oral penicillin V is the treatment of choice but requires a ten-day regimen. Intramuscular benzathine penicillin G as a single dose (<27kg: 600,000U; ≥27kg: 1,200,000U) represents an alternative. Patients cease to be contagious 24h after adequate treatment.6

The authors declare no conflict of interest.