Scarlet fever is an acute respiratory infectious disease caused by group A type R hemolytic streptococcus, transmitted through droplets or contaminated clothing and utensils. It predominantly occurs in winter and spring, with children aged 2 to 10 being the most susceptible. The pathogenic strains of this disease consist of five serotypes, the most common being type 27 (accounting for 1/4), type 1, type 28, etc. These strains are characterized by their ability to produce erythrogenic toxin, secrete various enzymes and exotoxins, and exhibit no cross-immunity between different types. Individuals who have previously contracted the disease can still develop scarlet fever again if infected with a different strain.

bubble_chart Clinical Manifestations

1. Common Type
   1. Prodromal Stage: Half a day to 1 day, sudden onset with high fever, sore throat, headache, often accompanied by vomiting. The pharynx and tonsils are markedly congested, with possible exudate. The tongue has a white coating, and the papillae are prominent, known as "white strawberry tongue."
   2. Stage of Full Eruption: 3–5 days. The eruption spreads rapidly from the neck and chest to the abdomen, back, and limbs, covering the entire body within a day. The face shows no rash but is congested, with pallor around the mouth, known as "circumoral pallor." The rash is diffuse, resembling foxtail millet grains, scarlet in color. In skin folds such as the elbows, front of the armpits, and groin, the rash is densely concentrated and linear, known as "Pastia's lines." During this stage, the tongue papillae become even more prominent, and the white coating peels off, forming the typical "strawberry tongue."
   3. Stage of Convalescence: Body temperature returns to normal, and the rash gradually fades without pigmentation, but there may be small or large patches of desquamation. In severe cases, the peeling may resemble gloves or socks. Early treatment with penicillin may prevent this peeling.
2. Severe (Toxic) Scarlet Fever: Persistent high fever around 40°C for about a week. The rash appears as erythema or hemorrhagic spots, with severe systemic infection and toxic symptoms, such as drowsiness and convulsions. In some cases, unconsciousness may occur due to toxic encephalopathy, and toxic myocarditis may also develop.
3. Complications
   1. Suppurative Lesions: Otitis media, lymphadenitis, cellulitis, and septicemia.
   2. Allergic Diseases: Acute nephritis and wind-dampness heat, mostly occurring 2–4 weeks after the illness.

bubble_chart Auxiliary Examination

1. The total white blood cell count increases to 10-20×10⁹/L or higher, with neutrophils accounting for over 75%, showing a left shift, and toxic granules visible in the cytoplasm. During the stage of convalescence, eosinophils may increase to 5-10%.
2. Routine urine tests may reveal a small amount of protein, mostly transient. In cases complicated by nephritis, protein levels increase, and red blood cells, white blood cells, and casts may appear.
3. Throat secretion cultures may show growth of group A streptococcus. Immunofluorescence testing of throat swab smears can detect group A streptococcus. 4. Serological tests: Generally, the anti-streptolysin O (ASO) titer is above 1:400. The streptozyme slide test can detect multiple antibodies in the serum early, with few false positives, providing rapid results within 2 minutes, serving as an auxiliary diagnostic tool.

bubble_chart Diagnosis

Epidemiological history: There is often a history of scarlet fever exposure, especially in childcare institutions and elementary schools where cases are more common. The incubation period is 1 to 6 days, usually 1 to 2 days.

bubble_chart Treatment Measures

(1) General Treatment During the acute stage of full eruption, bed rest is advised, with a liquid or semi-liquid diet. Intravenous fluids should be administered if oral intake is insufficient or if severe toxic symptoms are present.

(2) Antibiotic Therapy

1. Penicillin is the drug of choice. Early administration can shorten the course of the disease and reduce complications. The dose is 800,000 to 1.6 million units per day, administered via intramuscular injection, intravenous drip, or in combination with another antibiotic. For severe cases, the dose may be increased to 3.2 to 4.8 million units per day, with a treatment duration of 7 to 10 days.
2. For patients unable to receive injections, oral cephalosporin antibiotics such as cefradine (Cefradine VI), cefaclor (Ceclor), or amoxicillin, ampicillin, etc., may be used for one week.
3. For patients allergic to penicillin, macrolide antibiotics such as erythromycin, roxithromycin, or azithromycin may be administered via injection or orally for one week.

(3) Treatment of Complications

1. For suppurative complications, the dose of penicillin may be increased before penicillin treatment is initiated. If complications occur after penicillin treatment, switching to another antibiotic should be considered.
2. For complications such as myocarditis or wind-dampness fever, treatment should follow protocols for myocarditis and anti-wind-dampness therapy. If acute glomerulonephritis occurs, it should be managed as acute nephritis.

bubble_chart Prevention

1. Isolate the affected child until symptoms and rash disappear, or for 1 week after treatment. Strict isolation should continue until three consecutive throat cultures are negative. Close contacts should be quarantined for 7 to 12 days.
2. Protect susceptible populations. During outbreaks, children should avoid public places. In collective childcare settings, each child can receive a single injection of long-acting penicillin at 1.2 million units per dose to halt the outbreak. Close contacts may be given penicillin injections for 3 to 4 days, or sulfonamide drugs can be used, typically choosing compound formula co-trimoxazole for 3 days. The latter is less effective.
3. Group B streptococcus carriers should undergo 1 week of penicillin treatment. If they are childcare workers, they should be temporarily reassigned until throat swab cultures turn negative.

bubble_chart Differentiation

1. Staphylococcus aureus infection: Scarlet-like rashes may appear in suppurative lymph node infections and sepsis, which are transient without desquamation after the rash subsides. There is no "Chinese wax myrtle bark" tongue, but an infectious focus is present. Toxic symptoms remain severe after the rash fades, and penicillin is ineffective. Blood culture positive for Staphylococcus aureus should be used for differentiation.
2. Mucocutaneous lymph node syndrome: Also known as Kawasaki disease. Typically presents with fever lasting more than 5 days and may include scarlet-like rashes. The rash can appear on the face, trunk, and limbs with varying patterns, interspersed with normal skin. Hard edema is observed on the hands and feet, particularly at the fingertips, along with conjunctival congestion, lip fissures, and lymphadenopathy. Subsequently, membranous desquamation occurs on the nail bed skin, and platelets may increase.
3. Drug rash: History of medication use, with rashes predominantly on the cheeks and limbs, varying in morphology, and disappearing after discontinuation of the drug.