Scarlet fever is an infectious disease resulting from a group A streptococcus (group A strep) infection, also known as Streptococcus pyogenes. The signs and symptoms include a sore throat, fever, headaches, swollen lymph nodes, and a characteristic rash. The rash is red and feels like sandpaper and the tongue may be red and bumpy. It most commonly affects children between five and 15 years of age.Scarlet fever affects a small number of people who have strep throat or streptococcal skin infections. The bacteria are usually spread by people coughing or sneezing. It can also be spread when a person touches an object that has the bacteria on it and then touches their mouth or nose. The characteristic rash is due to the erythrogenic toxin, a substance produced by some types of the bacterium. The diagnosis is typically confirmed by culturing the throat.There is no vaccine for scarlet fever. Prevention is by frequent handwashing, not sharing personal items, and staying away from other people when sick. The disease is treatable with antibiotics, which prevent most complications. Outcomes with scarlet fever are typically good if treated. Long-term complications as a result of scarlet fever include kidney disease, rheumatic heart disease, and arthritis. In the early 20th century, before antibiotics were available, it was a leading cause of death in children.
This means that if the result is positive (indicating that the group A strep antigen was detected and therefore confirming that the person has a group A strep pharyngitis), then it is appropriate to treat the people with scarlet fever with antibiotics. But, if the rapid antigen detection test is negative (indicating that they do not have group A strep pharyngitis), then a throat culture is required to confirm, as the first test could have yielded a false negative result. In the early 21st century, the throat culture is the current "gold standard" for diagnosis.Serologic testing seeks evidence of the antibodies that the body produces against the streptococcal infection, including antistreptolysin-O and antideoxyribonuclease B. It takes the body 2–3 weeks to make these antibodies, so this type of testing is not useful for diagnosing a current infection. But, it is useful when assessing a person who may have one of the complications from a previous streptococcal infection.Throat cultures done after antibiotic therapy can show if the infection has been removed. These throat swabs, however, are not indicated, because up to 25% of properly treated individuals can continue to carry the streptococcal infection while being asymptomatic. Differential diagnosis
Viral exanthem: Viral infections are often accompanied by a rash which can be described as morbilliform or maculopapular. This type of rash is accompanied by a prodromal period of cough and runny nose in addition to a fever, indicative of a viral process.