bubble_chart Overview

Scarlet fever is an acute respiratory infectious disease characterized by fever, pharyngitis, and a rash.

bubble_chart Etiology

Group A β-hemolytic streptococci are classified into 80 types (types) based on the antigenic differences of the bacterial M protein. Each type can produce corresponding specific antibodies without cross-immunity. The heat toxins include three types: A, B, and C. After infection with one type, encountering any other type can still result in a second or third case of scarlet fever, although such occurrences are rare.

bubble_chart Pathological Changes

Pathogenic bacteria and their toxins cause inflammation and suppurative changes at the site of invasion and surrounding tissues, enter the bloodstream, leading to sepsis, and induce fever and rash due to heat toxins. The main pathological changes include congestion and edema of capillaries in the dermis, inflammatory exudation in the epidermis, edema around hair follicles, epithelial cell proliferation, and inflammatory cell infiltration, manifesting as papular rash-like lesions. During the stage of convalescence, the epidermis undergoes keratinization, necrosis, and large-scale shedding. In rare cases, toxic myocarditis, as well as congestion of the liver, spleen, and lymph nodes, may be observed.

bubble_chart Clinical Manifestations

The incubation period is generally 2 to 4 days, with a minimum of 1 day and a maximum of 7 days. The onset is abrupt, with shivering and fever, and the body temperature is usually 38–39°C, but can reach above 40°C in severe cases. Infants and young children may experience convulsions or delirium. The child experiences general malaise, with significant sore throat that affects eating. The pharynx and tonsils are markedly congested, and purulent exudate may also be seen. The tongue texture is red, with swollen papillae resembling a strawberry, hence called "strawberry tongue." The cervical and submandibular lymph nodes are enlarged and tender.

The rash appears rapidly about 24 hours after the onset of illness, initially seen in the armpits, groin, and neck, and spreads over the entire body within 24 hours. The rash consists of diffuse scarlet-red pinpoint-sized papules, which feel like coarse sandpaper or resemble goosebumps in cold weather. The skin between the rashes is flushed and turns white temporarily when pressed. The cheeks are flushed and free of papules, while the skin around the mouth is pale, forming a circumoral pallor. In skin folds such as the armpits, elbows, and groin, the rash is dense and deep red, with pinpoint-sized hemorrhagic spots, forming a deep red transverse "Pastia's sign." Oral mucosa may also show mucosal rash, congestion, or petechiae. Fever persists during the stage of full eruption.

Desquamation begins at the end of the first week of illness, which is one of the characteristic symptoms of scarlet fever. It first appears on the face, then spreads to the trunk, limbs, and palms/soles. Facial desquamation occurs, while the trunk, hands, and feet may experience large-scale peeling, resembling glove or sock patterns. The degree of desquamation correlates with the severity of the rash, usually clearing completely in 2–4 weeks without leaving pigmentation.

The blanching test involves intradermal injection of heat-toxin antibodies to observe whether the child's rash is caused by heat toxin. The Dick test involves injecting heat toxin to detect the presence of antibodies in the body. Although most cases are of the ordinary type, clinical severity varies greatly, especially with the availability of effective penicillin treatment, leading to significant changes in the manifestations of scarlet fever, with severe infections being extremely rare.

1. Mild type: Throughout the course of the illness, characteristic symptoms are absent. There may be low-grade fever for 1–2 days or no fever, and the rash is highly atypical, possibly limited to the armpits and groin, sparse and faint, disappearing within 1–2 days. Strawberry tongue is absent. One week after onset, mild desquamation or peeling may be noticed on the forehead, ear pinna, and fingertips/toes, at which point the diagnosis of scarlet fever is considered. Due to the likelihood of misdiagnosis and inadequate treatment, the risk of secondary nephritis may increase.

2. Toxic type: Sudden fever exceeding 40.5°C, with pronounced systemic toxic symptoms such as convulsions, vomiting, and headache. The pharynx and soft palate are severely congested, with red macules and papules, and the tonsils may have purulent exudate, necrosis, ulceration, or pseudomembrane-like lesions. The rash appears quickly, often with numerous petechiae. If treatment is delayed, it may lead to septic symptoms, peritonsillar abscess formation, tonsillar ulceration, and infection spreading to the middle ear, mastoid, or maxillary sinus. Lymph nodes may be significantly swollen or develop cellulitis. More severe cases include sepsis, shock, or secondary metastatic purulent lesions.

bubble_chart Diagnosis

The diagnosis of typical cases is relatively straightforward, with elevated white blood cell and neutrophil counts in the child's peripheral blood. Confirmation requires a positive throat swab culture for group A beta-hemolytic streptococcus. Insufficient antibodies are present. Due to the presence of more than one toxin, its diagnostic significance is limited.

bubble_chart Treatment Measures

Penicillin is the antibiotic of choice for treating scarlet fever and all streptococcal infections. Generally, penicillin G is administered by injection for a course of 7 to 10 days, followed by a throat culture after discontinuation. For those allergic to penicillin, erythromycin can be taken orally or cephalosporins can be used, with the treatment course lasting no less than 7 days. In severe cases, intravenous administration or a combination of two antibiotics may be applied.

During the acute phase, children should rest in bed, and older children can gargle with warm saline solution. The diet should consist of liquid or semi-liquid foods. The skin should be kept clean, and calamine lotion can be applied to reduce cutaneous pruritus.

bubble_chart Prognosis

Early detection and prompt treatment with penicillin can lead to a quick cure. Severe cases and those with serious suppurative lesions are rarely seen, but allergic nephritis or wind-dampness fever may still occur after recovery from scarlet fever.

bubble_chart Prevention

Currently, there is no automatic immunizing agent for this disease, and prevention focuses on controlling the spread of infection. Isolate affected children until two consecutive throat cultures are negative. For weak individuals and close contacts with compromised immune function, they should take compound formula SMZ or receive penicillin injections for prevention. Carriers should undergo a 10-day penicillin treatment.

bubble_chart Differentiation

Many pathogenic infections can cause pharyngitis, and many diseases present with rashes or scarlet fever-like rashes, all of which should be carefully differentiated clinically. Examples include viral pharyngitis, infectious mononucleosis, diphtheria; eruptive diseases such as measles, rubella, drug rash, summer prickly heat; as well as Staphylococcus aureus infections and Kawasaki disease.