scarlet fever

scarlet fever, acute infectious disease caused by group A hemolytic streptococcal bacteria, in particular Streptococcus pyogenes. Scarlet fever can affect people of all ages, but it is most often seen in children. It is called scarlet fever because of the red skin rash that accompanies it.

Before the advent of antibiotics, scarlet fever was extremely serious, often causing long periods of illness, many dangerous complications, and even death. Children with scarlet fever used to be immediately isolated and quarantined, and entire schools and neighbourhoods panicked when a case was discovered. Today, however, scarlet fever has declined in incidence and, when it does occur, in severity. Recovery is rapid and complete when antibiotics are administered promptly, and most of the potentially dangerous complications can be prevented if the full course of treatment is followed.

Scarlet fever is almost identical to streptococcal pharyngitis, commonly called strep throat, and is frequently referred to as “strep throat with a rash.” The major difference between the two illnesses is that the scarlet fever bacterium gives rise to an antigen called the erythrogenic (“redness-producing”) toxin, which is responsible for the characteristic rash.

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The course of the disease

Scarlet fever is rarely seen in infants and toddlers, but it begins to increase in incidence gradually after two years of age and reaches a peak incidence just before adolescence, being most common between ages 6 and 12. It is more common in temperate areas than in warmer tropical areas. The main sources of infection are the noses and throats of infected persons, who frequently spray droplets into the air by sneezing or coughing. Bacteria can also be transmitted indirectly by contact with contaminated objects or the unwashed hands of an infected person.

The incubation period of the scarlet fever bacterium ranges between one and seven days. The illness usually begins with a sudden onset of fever, vomiting, and severe sore throat. Along with these symptoms the child usually develops a headache, chills, and weakness. Between 12 and 24 hours after the onset of fever, the typical scarlet rash appears. Occasionally the child complains of severe abdominal pain.

In a typical case the temperature rises to 39.5 °C (103 °F) or higher. The throat is red and sore, and the tonsils are enlarged, reddened, and covered with patches of exudate. The glands under the angles of the jaw become swollen and tender. The tongue changes its appearance as the disease progresses. At the start the tip and edges are reddened, and the rest of the tongue has a whitish appearance. By the third or fourth day the white coat has peeled off, and the tongue then develops a red “strawberry” appearance.

The scarlet fever rash, which appears shortly after the fever, has been described as a “sunburn with goose pimples.” The skin is covered with tiny red spots that blanch on pressure and has a rough sandpaper-like texture. This scarlet rash usually covers the entire body except for the area around the mouth, which remains pale. One of the most characteristic features of the rash is desquamation, or peeling, which occurs at the end of the first week. Desquamating skin comes off as fine flakes like bran. The hands and feet are usually the last to desquamate—not until the second or third week of the illness.

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Diagnosis and treatment

Most cases of scarlet fever can be diagnosed by the typical signs and symptoms alone. The most useful means of confirming a diagnosis is throat culture. Group A hemolytic streptococci can be isolated from the throat or nose by using a cotton swab, and the results of the culture can be determined after only 24 hours of incubation. Blood samples can also be drawn and checked for elevated white blood cell levels or for antibodies to various of the toxins given off by the streptococci, but these tests are rarely needed for diagnosis.

A number of antibiotics are effective in the treatment of group A streptococcal infections, but penicillin remains the drug of choice. The drug can be given by injection or by mouth. Treatment consistently results in rapid reduction of fever and improvement in well-being. The aim is to maintain an adequate blood level of penicillin against the bacteria for at least 10 days of treatment. The danger is that often, with the child feeling better after only two or three days, treatment is stopped too soon. For this reason doctors occasionally treat patients by injection of a single long-acting penicillin preparation. For children who are allergic to penicillin, there are a number of other equally effective antibiotics—for example, erythromycin.

Complications

Early complications of scarlet fever generally occur during the first week of illness. The infection may spread, causing inflammation of the middle ear (otitis media), the paranasal sinuses (sinusitis), or the lymph nodes of the neck. A rare early complication is bronchial pneumonia. Even rarer are osteomyelitis (infection of the bone), mastoiditis (infection of the bony areas behind the ears), and septicemia (blood poisoning). If the child is adequately treated, such complications rarely develop.

Of great importance are two serious late complications, rheumatic fever (inflammation of the heart and joints) and glomerulonephritis (inflammation of the urine-producing structures of the kidney). These late complications are probably caused by an autoimmune reaction brought on by the streptococci or some of their by-products. Onset varies from one to two weeks for glomerulonephritis and from two to four weeks for rheumatic fever. They may follow a mild streptococcal infection just as often as a severe one.

Rheumatic fever is relatively uncommon but serious. The incidence is said to be about 3 percent after a case of streptococcal infection that is inadequately treated and less than 1 percent after full treatment. Rheumatic fever is rarely seen in children under age three. Since rheumatic fever often causes damage to the heart, it is extremely important that any child with a streptococcal infection be correctly diagnosed and adequately treated.

Glomerulonephritis (also called Bright disease) is a more common late complication. A child who develops acute glomerulonephritis has fever, blood in the urine, puffiness in the face, and, occasionally, high blood pressure. However, in most cases the prognosis for full recovery is excellent.