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In the light of the current outbreak of scarlet fever, which has seen the number of cases double in the first three months of the year compared with the same period in 2017, this is a timely reminder of the presentation and prognosis of the infection, including mechanisms of transmission, when to take a throat swab and culture, differential diagnosis and complications.
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Dr Nigel Stollery, GP, Leicestershire, Clinical assistant in dermatology at Leicester Royal Infirmary
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PRACTICE NURSE FEATURED ARTICLE
Infectious diseases in children: Scarlet fever Dr Mary Lowth
Scarlet fever, previously known as scarlatina, consists of a syndrome characterised by a fever, bright red exanthem and an exudative pharyngitis. It is caused by the toxin-producing group A beta-haemolytic streptococci (GABHS).
Numbers of UK cases are currently higher than at any time since 1982, when Public Health England (PHE) began collecting data. PHE recorded 15,549 scarlet fever notifications in the first three months of 2018, more than twice as many as last year, and 20,372 cases since September 2017.1 Notifications peaked in the last week of March, when 2,105 cases were reported.
The condition most commonly affects the five to 15 years age group and is most common in the winter and spring. It is rare in the under-twos, due to the presence of maternal anti-exotoxin antibodies.
The most common form of transmission is by respiratory droplets in close contact, but the ability of the organism to survive variations in temperature and humidity means spread via fomites can occur.
Hand washing and covering the mouth when coughing and sneezing should be encouraged to prevent the spread of the condition where outbreaks are reported.
Rarely, transmission can occur via food. This was the reported cause of an outbreak in China.2
Males and females are equally affected, with no ethnic variations. The incubation period varies from 12 hours to seven days.
Onset is usually rapid, with fever, sore throat, vomiting, headache, abdominal pain, myalgia and malaise. This is followed 12-48 hours later by a rash, which usually starts on the neck then extends to the trunk and extremities.
The rash occurs as a result of the local production of inflammatory mediators and alteration of the cutaneous cytokine milieu, resulting in dilation of blood vessels and the characteristic scarlet appearance of the rash.3
The rash is a fine erythematous punctate eruption, which blanches with pressure. This is followed by dry rough skin, with the feel of sandpaper. Seven to 10 days later, desquamation will occur of all affected areas, which may last on the palms for up to a month.
The fever peaks on the second day and will usually settle in 5 to 7 days.
The tongue is usually heavily coated, with the papillae visible through the coating. This coating sloughs off, leaving a red, shiny, so-called strawberry tongue, with prominent papillae. The pharynx and tonsils will have a typical thick exudate, similar to that seen in bacterial tonsillitis or glandular fever.
Investigations are not always required and the diagnosis can usually be made clinically, based on the rash and symptoms. The condition usually occurs in outbreaks, which can also help with the diagnosis.
A throat swab and culture and antistreptolysin O titres can be helpful if the diagnosis is in doubt.
The carriage rate of GABHS in healthy individuals is 10-15%, so a positive swab is not proof of the disease.
The treatment of choice is 10 days of penicillin VK or a cephalosporin. In those who have a documented allergy to penicillin, erythromycin should be used as an alternative.
Children can return to school 24 hours after starting the antibiotics if they are systemically well enough.
Patient education is very important – symptoms will often settle over a few days, but it is essential to complete the course of antibiotics, to prevent the development of complications (see box 1).
BOX 1 SCARLET FEVER
BOX 2. COMPLICATIONS
Symptomatic treatment, such as paracetomol, can help with the fever, and fluids should be maintained to prevent dehydration.
For the skin desquamation, emollients should be advised, with antihistamines for any pruritus. Topical steroids are of little help.
The prognosis is usually excellent, with most patients recovering after four to five days and the rash clearing over four to five weeks. This was not the case in the days before antibiotics, when mortality was as high as 15-20% of those affected.
At present, there is no vaccine against this condition, but it is thought that by 10 years of age, 80% of the population will have developed lifelong immunity to the causative organism.
1. PHE. April 2018. Health Protection Report. Group A streptococcal infections, third report on seasonal activity, 2017 to 2018. https://www.gov.uk/government/publications/group-a-streptococcal-infections-activity-during-the-2017-to-2018-season
2. Yang SG, Dong HJ, Li FR et al. Report and analysis of a scarlet fever outbreak among adults through food-borne transmission in China J Infect 2007; 55(5): 419-24 https://www.ncbi.nlm.nih.gov/pubmed/17719644
3. Cunningham MW. Pathogenesis of group A streptococcal infections. Clin Microbiol Rev 2000; 13(3): 470-511 https://www.ncbi.nlm.nih.gov/pubmed/10885988