Scarlet fever

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[edit] Scarlet Fever

Scarlet fever is one of the six childhood rashes , but is rare now in the US, although still common in development countries. It is produced by a group of bacteria that belong into the group A streptococcus family (Streptococcus pyogenes) and has a short incubation time of only 1 to 3 days. There are over 130 different strains of streptococci that cause such variety of conditions as tonsillitis, pharyngitis, cellulitis, pneumonia, rheumatic fever, rheumatic heart valve disease, acute glomerulonephritis, septicemia, Sydenham chorea, streptococcal puerperal fever and toxic shock syndrome. Scarlet fever is caused by a type of group A streptococcus that produces a pyrogenic enzyme that is also termed “erythrogenic”. This toxin causes all of the symptoms of scarlet fever such as fever (pyrogenic). The term “erythrogenic” comes from the laboratory where a throat swab is screened for bacteria producing the pyrogenic toxin on a special agar plate that contains sheep red blood cells. When the group A streptococcus type is found that is associated with scarlet fever a yellow colony of beta-hemolytic streptococci is surrounded with a ring where red blood cells have been destroyed against the background of the red agar Petri dish as shown in this link. This is a very specific lab result that demonstrates whether or not scarlet fever streptococci were present in this swab. It is the toxin that causes fever, the skin rash, any joint or heart disease, kidney damage or seizures (toxic effect on the brain) as a result of scarlet fever. The case fatality in some development countries is as high as 3% with an epidemic.

Signs and symptoms: The symptoms occur as a result of the toxin produced by the hemolytic group A streptococci. The more bacteria multiply, the sicker the patient gets. Initially the patient develops a sore throat, high fever and a strawberry tongue. The patient may feel nausea and may vomit. The physician sees a bright red pharynx (beef-colored) and tonsillitis with a pussy exudate. There can be a pale skin area around the mouth (circumoral pallor) and flushing of the cheeks. Within two to three days from the beginning of the infection a typical scarlet fever rash occurs sparing the face, starting at the neck and going to the chest and to the extremities. The folds of the axilla, the elbows, the groin and the inner aspect of the thighs are also often affected. This is sometimes better to feel (like sandpaper) than to see. The rash has fine reddish points which blanch with pressure application. Sometimes the rash presents with dark red lines on the side of the chest or in skin folds (Pastia’s lines).

During the recovery phase of scarlet fever there is often peeling of skin (desquamation) on the tip of the fingers or of the toes, on the trunk or on the palms of the hands or soles of the feet. Usually this happens in areas where the skin rash was most severe.

Diagnosis:

The diagnosis is clinical, but is aided by a throat swab, if in doubt. As already stated the culture is done on sheep blood agar plates. A quick test can be done as well with a throat swab (rapid antigen detection test), which is specific for group A beta-hemolytic streptococcus. This test is highly sensitive, but another quick test (optical immunoassay) is lacking sensitivity and could be falsely negative (only 60 to 80% sensitivity). It is recommended in such a negative optical immunoassay to do a regular culture test, which takes 1 to 2 days.

Treatment:

Amazingly penicillin is still the most effective antibiotic against scarlet fever. In children less than 60 lbs. 600,000 units of benzathine penicillin is given intramuscularly. Adolescents and adults get 1.2 million units intramuscularly. It has been shown that delaying treatment by 1 or 2 days to await the culture results does not prolong the duration of the illness or lead to more complications. On the other hand, if the patient does not want to take an injection, a full course of antibiotics has to be taken for 10 days (no skipping of doses). Alternative antibiotics are oral amoxicillin; and for patients allergic to penicillin erythromycin, clindamycin and cephazolin can be used.

Complications:

Three separate erythrogenic toxins have been described, which means that it is possible to get scarlet fever several times, as these group A beta-hemolytic streptococci strains are antigenetically different. You get a life-long immunity when affected by one strain, but you are still susceptible to the other two etc. At this point researchers have not succeeded in developing an effective vaccine. Several important complications can occur about 2 to 3 weeks after the start of scarlet fever. One complication is rheumatic fever that affects the joints, but can also damage the heart valves and in later life can lead to mitral stenosis. Another complication is an inflammatory kidney disease, called acute glomerulonephritis. Unfortunately this can turn chronic and may require dialysis or a kidney transplant later in life. Serious skin infections can occur such as streptococcal impetigo and erysipelas. Necrotizing fasciitis (= flesh eating disease) is from Streptococcus pyogenes and spreads along fascial planes, deep under the skin. Sydenham chorea is a complication in some of those children who develop rheumatic fever. It is usually self limiting,

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References: 1. David Heymann, MD, editor: Control of Communicable Diseases Manual, American Public Health Association, 2004. 2. The Merck Manual,18th edition. Merck&Co., 2006.