Editing Scarlet fever (section)

==Diagnosis==
Although the presentation of scarlet fever can be clinically diagnosed, further testing may be required to distinguish it from other illnesses.<ref name=Zitelli2023/> Also, history of a recent exposure to someone with [[strep throat]] can be useful in diagnosis.<ref name="Nelson2016" /> There are two methods used to confirm suspicion of scarlet fever; [[rapid antigen detection test]] and [[throat culture]].<ref name="Langlois-2011"/>

The rapid antigen detection test is a very [[Sensitivity and specificity|specific test]] but not very sensitive. 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 positives and false negatives|false negative]] result.<ref name=Baker2013>{{Cite book|title=Red Book Atlas of Pediatric Infectious Diseases|last=American Academy of Pediatrics|publisher=American Academy of Pediatrics|year=2013|isbn=9781581107951|editor-last=Baker|editor-first=Carol|pages=473–476}}</ref> In the early 21st century, the throat culture is the current "gold standard" for diagnosis.<ref name="Langlois-2011"/>

[[Serology|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.<ref name="Usatine-2013"/><ref name="Langlois-2011"/>

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.<ref name="Tanz-2018" />

===Differential diagnosis===
Scarlet fever might appear similar to [[Kawasaki disease]], which has a characteristic red but not white strawberry tongue, and [[Staphylococcal scarlet fever|staphylococcal scarlatina]] which does not have the strawberry tongue at all.<ref name=Andrew2020/> Other conditions that might appear similar include [[impetigo]], [[erysipelas]], [[measles]], [[chickenpox]], and [[hand-foot-and-mouth disease]], and may be distinguished by the pattern of symptoms.<ref name=Pardo2022/>

* Viral [[exanthem]]: Viral infections are often accompanied by a rash which can be described as [[morbilliform]] or [[Maculopapular rash|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.<ref name="Kaspar-2015"/>
* Allergic or [[contact dermatitis]]: The erythematous appearance of the skin will be in a more localized distribution rather than the diffuse and generalized rash seen in scarlet fever.<ref name="Usatine-2013"/>
* [[Drug eruption]]: These are potential side effects of taking certain drugs such as penicillin. The reddened maculopapular rash which results can be itchy and be accompanied by a fever.<ref>{{Cite book|title=Ferri's Color Atlas and Text of Clinical Medicine|last=Ferri|first=Fred|publisher=Saunders|year=2009|pages=47–48}}</ref>
* Kawasaki disease: Children with this disease also present with a strawberry tongue and undergo a desquamative process on their palms and soles. However, these children tend to be younger than five years old, their fever lasts longer (at least five days), and they have additional clinical criteria (including signs such as conjunctival redness and cracked lips), which can help distinguish this from scarlet fever.<ref>{{Cite book |title=Cardiology | edition=Third |last=Kato |first=Hirohisa|publisher=Elsevier |year=2010|pages=1613–1626}}</ref>
* [[Toxic shock syndrome]]: Both streptococcal and staphylococcal bacteria can cause this syndrome. Clinical manifestations include diffuse rash and desquamation of the palms and soles. It can be distinguished from scarlet fever by low blood pressure, lack of sandpaper texture for the rash, and multi-organ system involvement.<ref>{{Cite book|title=Clinical Dermatology|last=Habif|first=Thomas|publisher=Elsevier|year=2016|pages=534–576}}</ref>
* [[Staphylococcal scalded skin syndrome]]: This is a disease that occurs primarily in young children due to a toxin-producing strain of the bacteria ''Staphylococcus aureus''. The abrupt start of the fever and diffused sunburned appearance of the rash can resemble scarlet fever. However, this rash is associated with tenderness and large blister formation. These blisters easily pop, followed by causing the skin to peel.<ref>{{Cite book|title=Emergency Medicine Clinical Essentials|last=Adams|first=James|publisher=Saunders|year=2013|pages=149–158}}</ref>
* Staphylococcal scarlet fever: The rash is identical to the streptococcal scarlet fever in distribution and texture, but the skin affected by the rash will be tender.<ref name=Zitelli2023/>