Scarlet fever: causes, symptoms, diagnosis, and treatment

Scarlet fever is an acute respiratory infection caused by group A β hemolytic streptococcus and is characterized by fever, sore throat, generalized diffuse scarlet rashes, and posteruptive desquamation, mostly in winter and spring, mostly in children.


Causes

Scarlet fever is an acute infectious disease caused by group A β hemolytic streptococcus such as streptococcus pyogenes, which can produce pyrogenic exotoxin, also known as erythrotoxin, divided into three types according to antigenicity: A, B, and C. All three types of erythrotoxin can cause erythema and toxic symptoms, and type A erythrotoxin causes more serious symptoms. Cross protection of the antibodies produced against the three antigens is absent. It has also recently been suggested that rash is an allergic reaction to streptococcal pyrogenic exotoxin, rather than direct effect of erythrotoxin in the skin.

The source of infection is mainly patients and carriers, and it is transmitted mostly by droplets. It can also be transmitted through contaminated foods and utensils, occasionally skin wounds or parturient canals, causing surgical scarlet fever or obstetric scarlet fever.


Signs and Symptoms

The incubation period is 2 - 5 days.

Prodromal stage

Scarlet fever mainly occurs in children aged 1 - 10 years, with sudden onset, high fever, and sore throat, with convulsions in infants. The tonsils are red and swollen, with gray white exudative membranes. The soft palate mucosa is congested, with spotted erythema and scattered petechiae. In the early stage, lingual papillae are red, swollen, and hypertrophied, protruding in the white tongue coat, which is called white strawberry tongue. The white tongue coat is exfoliated in 3 - 4 days, and the tongue is bright red, with red and swollen lingual papillae, which is called red strawberry tongue. Submandibular lymph nodes are swollen. In surgical or obstetric scarlet fever, pharyngeal symptoms are absent, obvious tenderness and a small amount of serous secretions in the wound are present, and the rash around the wound is also obvious.

Eruptive stage

Eruption occurs 1 day after onset, in the neck, chest, trunk, and limbs in sequence, and spreads throughout the whole body within about 36 hours. Skin lesions are diffuse, small, dense, blanching, sunburn-like erythema. In the skin folds, such as the elbow fossa, armpits, and groins, skin lesions are denser, and deep red punctate lines, known as Pastia lines, are present. The cheeks and forehead are congested and flushing, without rash. Characteristic circumoral pallor is present. The rash can reach a peak within 48 hours after onset and is diffusely scarlet. Hemorrhagic rash may occur in severe patients. Increased capillary fragility and positive result in tourniquet test are present and can be accompanied by thrombocytopenia. Skin lesions subside in the order of eruption in 2 - 4 days.

Recovery stage

Desquamation occurs 7 - 8 days after onset, initially from the periotic area, followed by the trunk and limbs. Tiny desquamation in the face and trunk and large desquamation, sometimes glove-like and sock-like desquamation, in the palms and soles are present. Hair loss can be temporarily present, and transverse furrows of nails can occur in severe patients.

White blood cell count is increased, up to 10 – 20 × 109/L, neutrophils are increased by more than 80%, neutrophil left lift is present, toxic granulation and Dohle bodies are visible in cytoplasm, and eosinophils is absent in the early stage but increased in the recovery stage.


Histopathology

Microvascular vasodilatation, congestion, edema, neutrophil infiltration, mucosal congestion, and sometimes punctiform hemorrhage, caused by erythrotoxin, can be seen. Myocardial opacification, swelling, and degeneration, and necrosis in severe cases are visible. Interstitial mononuclear cell infiltration is present and different degrees of hyperemia in the liver, spleen, and lymph nodes are visible. Interstitial nephritis is present.


Diagnosis

On the basis of a history of exposure to patients with scarlet fever, clinical manifestations such as sudden fever, sore throat, typical skin lesions, circumoral pallor, strawberry tongue, Pastia lines, and desquamation, diagnosis is not difficult.

Differential diagnosis

Measles is characterized by catarrh in upper respiratory tract in the early stage, eruption 3 – 4 days after onset, normal skin between rashes, facial rashes, and Koplik's spots.

Rubella is manifested by eruption on the first day of onset, skin lesions similar to scarlet fever but without diffuse skin flushing, absent desquamation, and postauricular and suboccipital lymph node enlargement.

Drug eruption is with a history of drugs. Skin lesions are sometimes diversified and unevenly distributed, and occur from the trunk to extremities. Systemic symptoms are mild and not commensurate with the severity of rashes. Sore throat, strawberry tongue, and cervical lymph node enlargement are absent.

Staphylococcus aureus infection can be differentiated mainly based on bacterial culture.

Kawasaki disease, also known as mucocutaneous lymph node syndrome, mostly in children under 4 years of age, is mainly manifested by acute onset, 1 - 2 weeks of fever, conjunctival hyperemia, strawberry tongue, oral congestion, cervical, submandibular, and inguinal lymphadenopathy, absent suppuration, absent adhesion, symmetrical edema at the end of digits, pleomorphic skin lesions mainly in the trunk, absent or mild pruritus, and desquamation. The disease is often accompanied by cardiovascular, digestive tract, and urinary tract disease.


Treatment

Penicillin is the first choice for the treatment of scarlet fever and all streptococcal infections. Early application can shorten the course and reduce complications. The treatment regimen is penicillin 40,000 - 80,000 U / (kg.d) IV twice a day for at least 10 days. Under severe conditions, doses can be increased. Patients allergic to penicillin can take erythromycin 20 - 40mg / (kg · d) orally 3 times a day for 7 – 10 days, and intravenous injection can also be used in severe cases.