Scarlet Fever

Causes and routes of transmission

The causative agent of the disease is the gram-positive coccus Streptococcus pyogenes (group A beta-hemolytic streptococcus, or GAS). A crucial condition for the development of scarlet fever specifically is infection with a toxigenic strain capable of producing erythrogenic toxin. The bacterium is stable in the external environment (resistant to freezing and drying), but is rapidly killed by antibiotics and standard disinfectants.

The infection is transmitted exclusively from person to person (anthroponosis). The source can be a patient with scarlet fever (contagious from the first hours), a patient with another form of streptococcal infection, or a healthy carrier. The primary route of transmission is airborne droplets, although transmission via household items and toys is possible. Children aged 2 to 6 years and younger schoolchildren fall ill most often during the cold season; infants under one year old and adults rarely contract the disease.

Pathogenesis of infection

Scarlet fever develops in the absence of antitoxic immunity in an individual. The port of entry is most commonly the mucous membranes of the nasopharynx and oropharynx, but in atypical cases, the pathogen penetrates through damaged skin (burns, wounds).

A focus of inflammation and necrosis forms at the site of bacterial entry. The pathogenesis of the disease includes three components:

• Septic — direct damaging action of the bacteria themselves.
• Toxic — effect of the erythrogenic exotoxin, which is absorbed into the blood and causes intoxication, fever, and the appearance of a specific rash.
• Allergic — development of an allergic reaction of the body to the exotoxin, which peaks in the 2nd–3rd week of the disease and can cause late autoimmune complications.

Persistent antitoxic immunity is formed after recovering from scarlet fever.

Symptoms and clinical course

Following the incubation period (2–7 days), the disease begins acutely. Fever, symptoms of intoxication, and a sore throat appear. Oropharyngeal examination reveals tonsillitis (ranging from catarrhal to necrotic) with sharp redness, termed "fiery throat", along with enlarged cervical lymph nodes.

On days 1–2, a characteristic punctate rash appears on a red background. It is localized predominantly on the abdomen, chest, flexor surfaces of the arms, and inner thighs.

Specific signs of scarlet fever:

• Pastia's sign — clustering of the rash and formation of dark red lines in natural skin folds (armpits, groin, elbow creases).
• Filatov's sign — a pale nasolabial triangle devoid of rash, sharply contrasting with bright red cheeks.

After 2–5 days, the rash fades and the temperature drops. The tongue, initially covered with a thick white coating, clears and becomes "strawberry" due to its bright red color and enlarged papillae. In the second week, lamellar skin desquamation begins (especially on the palms and soles), the severity of which depends on the intensity of the rash in the first days.

Complications and treatment

Complications of scarlet fever are divided into early and late.

• Early complications arise due to the spread of infection (otitis media, lymphadenitis, synovitis). They are currently rare.
• Late complications develop in the 3rd–4th week and are associated with autoimmune (infectious-allergic) reactions. These include myocarditis, polyarthritis, and glomerulonephritis.

The mainstay of treatment is mandatory antibiotic therapy. The drugs of choice are penicillins (amoxicillin, benzylpenicillin), while macrolides are prescribed for penicillin allergies. The course usually lasts 5–7 days. Patients are prescribed bed rest during the fever and for 3 more days after temperature normalization, generous fluid intake, and a sparing diet.

Prevention and quarantine

There is no vaccine against scarlet fever. The main measures are isolation of patients and quarantine for contacts.

The patient is isolated for at least 10 days from the onset of the disease. For preschool children and 1st–2nd grade students, this period is extended—they are not allowed into the group for an additional 12 days (totaling 22 days of isolation). The kindergarten group that had contact with the patient is placed under quarantine for 7 days (according to some regulations, up to 22 days) with daily temperature monitoring and oropharyngeal examination.

Class and exam questions

What else to study on this topic

• Features of the clinical presentation of atypical forms of scarlet fever (toxic, septic, mild/abortive).
• Mechanism of development of late autoimmune complications (myocarditis, glomerulonephritis) and their prevention.
• Differential diagnosis of scarlet fever with measles, rubella, infectious mononucleosis, and drug-induced toxicoderma.
• Laboratory markers of streptococcal infection (streptolysin O, M protein) and their diagnostic significance.

Other topics from the section «Chapter 12. Infectious and parasitic diseases»

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