A 5 y.o. girl presents with fever and sore throat. One day later she develops a rash
What is your differential?
Our patient had scarlet fever. This consists of a fever + strep culture ( group A beta hemolytic strep ) and a rash which occurs one to two days later. The rash lasts for 7-10 weeks. Scarlet fever is part of a continuum of diseases caused by strep pyogenes including: strep throat with fever, scarlet fever, necrotizing fasciitis, and toxic shock . An autoimmune inflammatory disease can occur with any of these infections causing rheumatic fever and eventually rheumatic heart disease or post streptococcal glomerulonephritis.
The classic scarlet fever was associated with a virulent exotoxin resulting in 25% mortality. A world wide pandemic occurred in 1820-30. The classic findings were: fever, sore throat, strawberry tongue and skin desquamation.
strawberry tongue begins with redness and white patches and then swells.
Scarlet fever has become milder over the years and can be difficult to diagnose. This is attributed to a combination of factors including antibiotic availability, better nutrition/ social conditions, and evolution of the bacteria itself. Most individuals today who have strep pyogenes, as evidenced by ASO titers, have only a mild disease. However, the spectrum of disease caused by strep pyogenes is still present and outbreaks do occur.
impetigo is also caused by S pyogenes
About 15-20% of school aged children carry S pyogenes in their upper respiratory tract without any signs or symptoms of infection making a clinical diagnosis of scarlet fever more important than the throat culture alone. The extent to which a person will become ill depends on the production of a type of exotoxins called bacterial superantigens . In some patients, the release of group A Strep bacterial superantigens induce an immune response with cytokines. Maori and Pacific Islander children are more susceptible to complications of strep like rheumatic fever and rheumatic heart disease.
The superantigens SpeA, SpeC and SSA have been directly associated with scarlet fever.
Interesting facts
Some diseases evolve to be less virulent over time. Syphilis is a good example. It evolved into a less severe, chronic infection over time, likely due to natural selection favoring milder strains that facilitated easier transmission. Milder disease caused lesions which were less obvious.
Omicron was markedly less virulent than the delta virus strain of COVID. Spanish flu in 1918 became less virulent by 1920.
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Liang Y, Yu D,Lu Q, et al. The rise and fall of acute rheumatic fever and rheumatic heart disease: a mini review. Front Cardiovasc Med. 2023 May 23;10:1183606