Infectious Diseases

Updated 22 May 2015

Scarlet fever

Scarlet fever is a childhood illness featuring high fever.



  • Scarlet fever is linked to sore throats and sometimes to skin infections.
  • The streptococcus bacterium is responsible for about 15% of sore throats and a large proportion of skin infections in children.
  • Some strains of streptococcus produce a toxin that causes reddening of the skin, thus the name 'scarlet' fever.
  • The streptococcus bacterium is killed by penicillin, so scarlet fever can be treated with this medication.
  • Scarlet fever has become rare throughout the world, including South Africa. The reason for this is not completely understood.


Scarlet fever is a childhood illness featuring high fever, vomiting, headache, sore throat and a red, sandpaper-like rash of small red spots over the whole body. The skin redness can be turned pale by pressure on the skin. The redness of the rash is darkest under the arms, in the groin and in skin creases, for example at the elbows and knees. The rash will make a child appear sunburnt, with flushed red cheeks and forehead, but pale around the mouth. The tongue is also red, and the little protrusions on the tongue are swollen, giving it the appearance of "strawberry tongue". The throat and tonsils are inflamed.


The cause of scarlet fever is a toxin produced by particular bacteria called streptococci. Scarlet fever occurs as a complication of streptococcal sore throat if the particular streptococcus that is causing the sore throat has the ability to produce the specific toxin. Streptococci are bacteria and have this name because under the microscope they are seen to be round ("cocci"), and growing in strings ("strepto"). (The streptococci are a large family; those specifically responsible for scarlet fever are the so-called Group A beta-haemolytic streptococci.)

The bacteria may be found in low numbers in the throat and nose of healthy people who are carriers. In such people (up to one in five children) the bacterium has continued to live in the throat and nose after an infection. Streptococci can be spread from a carrier or from someone who is ill to another person by droplets from the nose or throat, by contact with infected skin, or via hands, food or drink.

At the place where the bacterium gets access to another person (usually the nose or throat, or broken skin), it will multiply. This attracts the body’s immune defences to the site, specifically white blood cells, which can migrate out of blood vessels into the tissues. White blood cells in large numbers form pus, which can be seen on the tonsils or in an infected area of skin.

Certain strains of streptococci are infected by a virus that causes them to produce a toxin when they multiply; only these strains can cause scarlet fever. The toxin spreads via the bloodstream and has the effect of turning the skin red. The toxin also contributes to other symptoms of scarlet fever such as the fever and "toxic" symptoms of hot and cold chills and a rapid pulse. For some reason the virus-infected strains of streptococci that can cause scarlet fever have virtually disappeared all around the world.


Scarlet fever was very common in Britain at the end of the 1800s but started to disappear at the turn of the century. The disease is seen very rarely today, possibly partly because streptococcal infections are treated early with antibiotics and this prevents the spread of strains that formerly could cause epidemics of scarlet fever.

Infections with streptococci and scarlet fever are usually seen in children older than three years. In young pre-school children scarlet fever may be linked to skin infection with streptococci, but in those older than five years it is much more commonly linked to throat infection.

Throat infections with streptococci are more common and severe in cold climates and in winter weather. Skin infections are more common in tropical climates and in warmer weather in other regions. Some skin infections with streptococci occur in normal skin, but others occur because of insect bites, scabies, chicken pox or minor injuries. Surgical wounds can become infected with streptococci, and scarlet fever in this situation is known as "surgical scarlet fever".


On average it takes three days after contact with an infected person for the illness to begin. The rash appears within a day or two after sore throat and other early symptoms. The fever can reach a height of 40 oC on the second day and will take up to a week to subside, unless a person is treated with penicillin, in which case it will be back to normal in about 12 hours. The rash fades by the end of a week but skin shedding continues for another three to six weeks.

Risk factors

Everyone is susceptible to streptococcal infections. Whether or not you develop scarlet fever depends only on whether you are infected with a strain of the streptococcus bacterium capable of producing the toxin. Although one will have several streptococcal infections in a lifetime, after one attack of scarlet fever a person is usually immune to the toxin and so a second attack of scarlet fever is rare.

When to see a doctor

All bad sore throats and possible scarlet fever cases should be seen by a health professional. While many sore throats are caused by viruses and do not warrant any treatment, any suspected streptococcal infection should be investigated and treated with an antibiotic.

There are several serious complications of streptococcal infections that can be wholly or completely avoided by proper treatment, namely:

  • Abscess formation around the tonsils
  • Spread of the bacteria to the lymph glands (adenitis)
  • Spread of the bacteria to the middle ear (otitis media)
  • Spread of the bacteria to the sinuses (sinusitis)
  • Spread of the bacteria via the bloodstream to the bones, joints or brain
  • Kidney damage (glomerulonephritis)
  • Rheumatic fever, which leads to damaged heart valves.


Scarlet fever can be confused with measles, rubella, roseola, glandular fever, diphtheria, Kawasaki disease, toxic shock syndrome and other rash diseases caused by viruses or drugs. Your health care worker would be able to exclude some of these possibilities by differences in the rash and other pointers. During an epidemic of scarlet fever it is easier to conclude that someone has the illness, but in a single case there may be doubt. The diagnosis would then best be confirmed by having a swab of the throat sent to the laboratory. A report of growth of streptococcus bacteria would be expected within 24 hours. In cases where the skin is suspected to be the origin of the streptococcus infection, a skin swab would be sent for culture.

Although blood tests are not generally indicated for sore throats or scarlet fever, a raised count of certain types of white cells would indicate a bacterial infection. In scarlet fever it is common to find an increased percentage of a special type of white cells known as eosinophils. An antibody test called an ASOT can specifically detect streptococcal infections, but it generally only becomes positive when the person is already recovering.



It is best to keep a child with a fever in bed. For the sore throat, body aches and fever, a painkiller and anti-pyretic (fever-reducing medication) such as paracetamol or mefenamic acid can be used. This will also help for painful swallowing. The drinking of cool drinks should be encouraged during the fever so that the child does not become dehydrated.


Penicillin is still the best antibiotic treatment for streptococcal infections, including scarlet fever. If a child is very ill, this might be given as an intra-muscular injection, but otherwise it would be given as an oral course lasting 10 days. As with any antibiotic, the course must be finished, even when the child appears and feels better. If a person is allergic to penicillin, there are other effective antibiotic options, such as erythromycin. It is very important to treat strongly suspected or proven streptococcal infections with an antibiotic, as several serious complications may occur. Antibiotics can usually be delayed without undue risk for a day or two until the laboratory result on a throat swab is received. If the result does not show streptococcal growth, unnecessary antibiotic treatment can be avoided.


It is practically impossible to avoid streptococcal infections, especially as they are often spread unknowingly by carriers who do not have any symptoms. In general it is advisable to avoid close contact with anyone who has an upper respiratory tract infection or a rash illness.

These days treatment with penicillin will rapidly eradicate a streptococcal infection from someone who has scarlet fever, so isolating him or her from others is not so important. If a child develops scarlet fever in an environment such as a school, his or her contacts can be treated if signs of the illness develop.

Reviewed by Dr Eftyhia Vardas BSc(Hons), MBBCh, DTM&H, DPH, FC Path (Virol), MMed (Virol), Clinical Virologist, Director HIV AIDS Vaccine Division, Perinatal HIV Research Unit, Chris Hani Baragwanath Hospital, University of the Witwatersrand and senior lecturer, Department of Infectious Diseases, Faculty of Health Sciences, University of the Witwatersrand.


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