Scarlet fever occurs when the infectious organism (usually a group A streptococcus) produces erythrogenic toxin in an individual who does not possess neutralizing antitoxin antibodies.
Clinical features
The incubation period of this relatively mild disease, which mainly affects children, is 2-4 days following a streptococcal infection, usually in the pharynx. Regional lymphadenopathy, fever, rigors, headache and vomiting are present. The rash, which blanches on pressure, usually appears on the second day of illness; it initially occurs on the neck but rapidly becomes punctate, erythematous and generalized. It is typically absent from the face, palms and soles, and is prominent in the flexures. The rash usually lasts about 5 days and is followed by extensive desquamation of the skin. The face is flushed, with characteristic circumoral pallor. Early in the disease the tongue has a white coating through which prominent bright red papillae can be seen ('strawberry tongue'). Later the white coating disappears, leaving a raw-looking, bright red colour ('raspberry tongue'). The patient is infective for 10-21 days after the onset of the rash, unless treated with penicillin.
Scarlet fever may be complicated by peritonsillar or retropharyngeal abscesses and otitis media.
Diagnosis
The diagnosis is established by the typical clinical features and culture of a throat swab. Elevated antistreptolysin O and anti-DNase B levels in convalescent serum are indicative of streptococcal infection.
Treatment
Penicillin is the drug of choice and is given orally as phenoxymethylpenicillin 500 mg four times daily for 10 days. Individuals allergic to penicillin can be treated effectively with erythromycin 250 mg four times daily for 10 days. Treatment is usually effective in preventing rheumatic fever and acute glomerulonephritis, which are non-suppurative complications of streptococcal pharyngitis. Unlike acute rheumatic fever, streptococcal nephritis may also complicate streptococcal skin infection.
Prevention
Chemoprophylaxis with penicillin or erythromycin should be given in epidemics.
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