Scarlet Fever

Streptococcus pyogenes, which is also called group A Streptococcus (group A strep), cause scarlet fever.

Etiology

Scarlet fever is an illness caused by pyrogenic exotoxin-producing S. pyogenes. S. pyogenes are gram-positive cocci that grow in chains (see Figure 1). They exhibit β-hemolysis (complete hemolysis) when grown on blood agar plates. They belong to group A in the Lancefield classification system for β-hemolytic Streptococcus, and thus are called group A streptococci.

Clinical features

Scarlet fever, also called scarlatina, is characterized by a scarlatiniform rash and usually occurs with group A strep pharyngitis. It can also follow group A strep pyoderma or wound infections.

Characteristics of the rash typically include:

• Erythematous rash that blanches on pressure
• Sandpaper quality
• Accentuation of the red rash in flexor creases (i.e., under the arm, in the groin), termed “Pastia’s lines”
• Begins on the trunk, then quickly spreads outward, usually sparing the palms and soles

The rash usually persists for about one week and desquamation may follow. In addition, the face may appear flushed and the area around the mouth may appear pale (i.e., circumoral pallor). A yellowish white coating with red papillae may initially cover the tongue. The eventual disappearance of the coating can result in a “strawberry tongue.”

Transmission

Group A strep infections, including scarlet fever, are most commonly spread through direct person-to-person transmission. Typically transmission occurs through saliva or nasal secretions from an infected person. People with scarlet fever are much more likely to transmit the bacteria to others than asymptomatic carriers. Crowded conditions — such as those in schools, military training facilities, or daycare centers — facilitate transmission. Although rare, spread of group A strep infections may also occur via food. Foodborne outbreaks of group A strep have occurred due to improper food handling. Environmental transmission via surfaces and fomites was historically not thought to occur. However, evidence from outbreak investigations indicate that environmental transmission of group A strep may be possible, although it is likely a less common route of transmission.

Humans are the primary reservoir for group A strep. There is no evidence to indicate that pets can transmit the bacteria to humans.

Treatment with an appropriate antibiotic for 12 hours or longer limits a person’s ability to transmit group A strep. People with scarlet fever should stay home from work, school, or daycare until:

• They are afebrile
  AND
• 12–24 hours after starting appropriate antibiotic therapy*

Incubation period

The incubation period of scarlet fever is approximately 2 through 5 days.

Risk factors

Scarlet fever can occur in people of all ages. It is most common among children 5 through 15 years of age. It is rare in children younger than 3 years of age.

The most common risk factor is close contact with another person with scarlet fever. Crowding, such as found in schools, military training facilities, and daycare centers, increases the risk of disease spread.

Diagnosis and testing

The differential diagnosis of scarlet fever with pharyngitis includes multiple viral pathogens that can cause acute pharyngitis with a viral exanthema. Clinicians need to use either a rapid antigen detection test (RADT) or throat culture to confirm scarlet fever with pharyngitis. RADTs have high specificity for group A strep but varying sensitivities when compared to throat culture. Throat culture is the gold standard diagnostic test. Clinicians should follow up a negative RADT in a child with symptoms of scarlet fever with a throat culture. Clinicians should have a mechanism to contact the family and initiate antibiotics if the back-up throat culture is positive.

See the resources section for specific diagnosis guidelines for adult and pediatric patients^1,2,3.

Treatment

The use of a recommended antibiotic regimen to treat scarlet fever:

• Shortens the duration of symptoms
• Reduces the likelihood of transmission to family members, classmates, and other close contacts
• Prevents the development of complications, including acute rheumatic fever

Penicillin or amoxicillin is the antibiotic of choice to treat scarlet fever. There has never been a report of a clinical isolate of group A strep that is resistant to penicillin. For patients with a penicillin allergy, recommended regimens include narrow-spectrum cephalosporins (e.g., cephalexin, cefadroxil), clindamycin, azithromycin, and clarithromycin.

See the resources section for specific treatment guidelines for adult and pediatric patients^1,2,3.

Related link: Amoxicillin Shortage: Antibiotic Options for Common Pediatric Conditions

Table: Antibiotic regimens recommended for group A streptococcal pharyngitis

From: Shulman ST, Bisno AL, Clegg HW, Gerber MA, Kaplan EL, Lee G, et al. Clinical Practice Guideline for the Diagnosis and Management of Group A Streptococcal Pharyngitis: 2012 Update by the Infectious Diseases Society of America. Clin Infect Dis. 2012;55(10):e86–e102, Table 2 (adapted).

Note: If you are interested in reusing this table, first obtain permission from the journal; request by emailing journals.permissions@oup.com.

Prognosis and complications

Rarely, complications can occur after scarlet fever. Scarlet fever can have the same suppurative and non-suppurative complications as group A strep pharyngitis. Suppurative complications result from local or hematogenous spread of the organism. They can include:

• Peritonsillar abscesses
• Retropharyngeal abscess
• Cervical lymphadenitis
• Invasive group A strep disease

Acute rheumatic fever is a nonsuppurative sequelae of group A strep pharyngitis. Post-streptococcal glomerulonephritis is a nonsuppurative sequelae of group A strep pharyngitis or skin infections. These complications occur after the original infection resolves and involve sites distant to the initial group A strep infection site. They are thought to be the result of the immune response and not of direct group A strep infection.

Prevention

Good hand hygiene and respiratory etiquette can reduce the spread of all types of group A strep infection. Hand hygiene is especially important after coughing and sneezing and before preparing foods or eating. Good respiratory etiquette involves covering your cough or sneeze. Treating an infected person with an antibiotic for 12 hours or longer limits their ability to transmit the bacteria. Thus, people with scarlet fever should stay home from work, school, or daycare until:

• They are afebrile
  AND
• At least 12-24 hours after starting appropriate antibiotic therapy*

Epidemiology and surveillance

Humans are the only reservoir for group A strep. It is most common among children 5 through 15 years of age. It is rare in children younger than 3 years of age. In the United States, scarlet fever is most common during the winter.

CDC does not track the incidence of scarlet fever or other non-invasive group A strep infections. CDC tracks invasive group A strep infections through the Active Bacterial Core surveillance (ABCs) program. For information on the incidence of invasive group A strep infections, please visit the ABCs Surveillance Reports website.

Footnote

Per the American Academy of Pediatrics Red Book 2021–2024, children with group A strep pharyngitis should not return to school or a childcare setting until well appearing and at least 12 hours after beginning appropriate antibiotic therapy.  In certain scenarios, such as an infection in a healthcare worker or in a group A strep outbreak setting, staying home for at least 24 hours after beginning appropriate antibiotics should be considered.