History and exam

Key diagnostic factors

common

presence of risk factors

Strong factors for scarlet fever are age 1 to 10 years at presentation, having group A streptococcus (GAS) pharyngitis, and being in close contact with a person with scarlet fever or other GAS presentation (e.g., GAS pharyngitis).

scarlatiniform rash

Present in 89% of children with scarlet fever.[18]

The characteristics of the rash include:[3][13]

  • Diffuse, finely papular (sandpaper like), erythematous rash that blanches with pressure

  • Accentuated in flexor creases (i.e., under the arm, in the groin, in the elbows) often with petechiae, producing red streaks known as Pastia's lines[27]

  • Starts on the trunk and may spread to the limbs (sparing palms and soles)

  • Flushed 'scarlet' bilateral cheeks with circumoral pallor. In patients with more darkly pigmented skin, flushed bilateral cheeks may appear 'sunburnt'.

[Figure caption and citation for the preceding image starts]: Typical scarlatiniform rash in a child with scarlet feverBMJ 2018; 362 :k3005. [Citation ends].com.bmj.content.model.Caption@6eea0f8f[Figure caption and citation for the preceding image starts]: Flushed bilateral cheeks with circumoral pallor in a child with scarlet feverFrom https://dermnetnz.org/topics/scarlet-fever used with permission [Citation ends].com.bmj.content.model.Caption@4361543d

In patients with more darkly pigmented skin, the rash has the same characteristic raised 'sandpaper' quality, but it may not appear erythematous.

fever (>38.0°C [>100.4°F])

Non-specific sign. Fever is the most common initial symptom, especially in children aged <5 years.[18]

sore throat

Common initial symptom in children ≥5 years with scarlet fever.[18] However, group A streptococcus is the cause of sore throat in less than one third of patients; viral aetiology is the most common cause in all age groups.[2]

tonsillopharyngeal inflammation

Non-specific sign, frequently seen in other diagnoses. Tonsillopharyngeal inflammation is one of the McIsaac (modified Centor) criteria for diagnosis of group A streptococcus pharyngitis, which is strongly associated with scarlet fever.[31][40]

tonsillopharyngeal exudate

Non-specific sign, frequently seen in other diagnoses. Tonsillopharyngeal exudate is one of the McIsaac (modified Centor) criteria for diagnosis of group A streptococcus pharyngitis, which is strongly associated with scarlet fever.[31][40]

palatal petechiae

Often associated with group A streptococcus (GAS) pharyngitis, which is strongly associated with scarlet fever. Although not included in the McIsaac (modified Centor) criteria for diagnosis of GAS pharyngitis, palatal petechiae is more specific (98%) for positive GAS throat culture than tonsillar exudates (86%) (which is included in the criteria).[41]

anterior cervical adenitis

Non-specific sign, frequently seen in other diagnoses. Enlarged tender anterior cervical lymph nodes is one of the McIsaac (modified Centor) criteria for diagnosis of group A streptococcus pharyngitis, which is strongly associated with scarlet fever.[31]

no cough

Lack of cough and other viral symptoms (e.g., rhinorrhoea, hoarseness, mouth ulcers) in the setting of fever and a scarlatiniform rash supports a diagnosis of scarlet fever. The presence of multiple viral symptoms is more helpful in ruling out group A streptococcus pharyngitis than the presence of an individual symptom.​[32]​​[33][42]

uncommon

pyoderma

Streptococcus pyogenes strains that produce pyrogenic exotoxins, which cause scarlet fever, may cause skin and soft-tissue infections. 

Other diagnostic factors

common

strawberry tongue

Inflammation of the tongue with a white coating and prominent papillae ('strawberry tongue') may be seen in patients with scarlet fever.[13]

[Figure caption and citation for the preceding image starts]: ​Strawberry tongue in a child with scarlet feverBMJ 2018; 362 :k3005 [Citation ends].com.bmj.content.model.Caption@52b33b3a

skin desquamation

Late finding (3-4 days after appearance of the scarlatiniform rash); fine peeling of the skin that starts on the head and progresses downwards.[13][27]

[Figure caption and citation for the preceding image starts]: Peeling phase of scarlatiniform rash in a patient with scarlet feverBMJ 2018; 362 :k3005 [Citation ends].com.bmj.content.model.Caption@42fde818

headache

Non-specific symptom in patients presenting with scarlet fever associated with group A streptococcus pharyngitis. May be present, especially in children.[2]

nausea

Non-specific symptom in patients presenting with scarlet fever associated with group A streptococcus pharyngitis. May be present, especially in children.[2]

vomiting

Non-specific symptom in patients presenting with scarlet fever associated with group A streptococcus pharyngitis. May be present, especially in children.[2]

abdominal pain

Non-specific symptom in patients presenting with scarlet fever associated with group A streptococcus pharyngitis. May be present, especially in children.[2]

Risk factors

strong

group A streptococcus (GAS) pharyngitis

Around 90% of cases of scarlet fever occur in conjunction with GAS pharyngitis (although <10% of patients with GAS pharyngitis develop scarlet fever); therefore, the presence of symptoms of scarlet fever (i.e., rash, fever, and sore throat) and a diagnosis of GAS pharyngitis are the most important clinical indicators of scarlet fever.[3][17][18]

GAS infection in children <3 years old is often associated with fever, mucopurulent rhinitis, excoriated nares, and diffuse adenopathy. Exudative pharyngitis is rare in this age group.[2]

Occasionally, especially in children <5 years of age, the scarlatiniform rash and fever can present prior to or independent of symptoms of pharyngitis.[18]

close contact with a person with scarlet fever or other group A streptococcus (GAS) presentation

The most common risk factor for scarlet fever is close contact with another person with the condition or other GAS presentation (e.g., GAS pharyngitis). Clusters or outbreaks of scarlet fever are commonly reported in endemic settings.[13] Household contacts of a person with scarlet fever have been found to have an increased risk of invasive GAS infection in the 2 months after scarlet fever onset, although the risk is relatively low (35.3 cases/100,000 person-years).[19] See Complications.

age 1 to 10 years

Scarlet fever can occur at any age but mainly affects children aged 1 to 10 years, and it is most common in those aged 3 to 6 years. Scarlet fever is uncommon in children <1 year old and in adults.[5][6][7]

weak

winter and spring seasons

In Europe and Asia, scarlet fever is most common during the winter and spring.[20]

crowded environment

Crowding, such as found in schools and nurseries, increases the risk of disease spread.[13]

close contact with children aged 1-10 years

Scarlet fever is uncommon in adults, but more common in adults living or working with young children (e.g., teachers, nursery workers, paediatric medical staff). This is reflected in higher rates of scarlet fever reported in adult women than men.[5][13]

non-pharyngitis group A streptococcus (GAS) infection

Around 90% of cases of scarlet fever occur in conjunction with GAS pharyngitis; however, it may also less commonly occur with GAS infection of the skin, soft tissue, and wounds.[3][21]

Necrotising fasciitis has not been associated with scarlet fever to date.[22]

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