Scarlet fever

What it is

Scarlet fever is a reaction to erythrogenic toxins produced by group A haemolytic streptococci. It is one of the non-suppurative complications of GAS infection, with rheumatic fever, post-infection glomerulonephritis and streptococcal toxic shock syndrome. Asked what causes it, the answer is GAS, group A streptococcus, which produces an erythrogenic exotoxin, and it is that exotoxin which causes the rash. Transmission is by direct contact or by respiratory droplets, and the incubation period is 2 to 5 days.

Causes and risk

It is common in children aged 2 to 6 years, with the peak incidence being at 4 years, while another page gives the age band as 5-15 years and the peak incidence of GAS infection of the throat is put at 5-12 years. Scarlet fever is spread via the respiratory route by inhaling or ingesting respiratory droplets, or by direct contact with nose and throat discharges, especially during sneezing and coughing.

The contagious period is until 24 hours after starting antibiotics, and the key point set beside it is that this is similar to the strep throat protocol. Keeping the child home until no longer contagious is the key point listed against impetigo in that same table, not against scarlet fever.