Scarlet Fever

What is Scarlet Fever?

Scarlet fever is an infection caused by bacteria; group A beta-haemolytic streptococci; called streptococcus pyogenes that is commonly seen in children from age 4-9 years old. This bacteria causes many other infections, commonly a sore throat and fever or an infected skin wound. It is a more common infection in children than in adult.

A very distinguish feature of Scarlet fever is the characteristic of the rash. The red skin rash that is usually at the chest, back and limbs. If diagnosed and treated early, Scarlet fever has a good outcome after being treated with antibiotics. Before the development and advancement of antibiotics, Scarlet fever has caused many deaths of young children in the past. However, even with advancement of antibiotics, complications of Scarlet fever can still happen and with mortality from severe infection.

scarlet fever

Streptococcus was first identified by Louis Pasteur and Theodor Billroth in 1870s. In 1884, a German physician named Friedrich Loeffler succeeding in relating Scarlet fever to streptococci by discovering the presence of streptococci found the in Scarlet fever patients. This association is later confirmed by Gladys Dick, George Dick and Alphonse Dochez.

In 1920s, Scarlet fever was known to be cause by group A streptococcus and its toxin. Scarlet fever was common then, and has caused many deaths of young children. After the discovery of penicillin, the incidence of Scarlet fever has dropped markedly with fewer deaths of young children from Scarlet fever.

Currently, Scarlet fever is only commonly seen in developing countries. Even so, the number of complications and mortality is much lesser compared to early 20th century. It is a notifiable disease in the United Kingdom.


  • Causes of Scarlet fever
  • Symptoms of Scarlet fever
  • Diagnosis and Investigation of Scarlet fever
  • Treatment of Scarlet fever
  • Prevention of Scarlet fever
  • Complication of Scarlet fever
  • Conclusion                                        

Causes of Scarlet fever

Scarlet fever is an infection caused by group A streptococcus, the streptococcus pyrogenes, a gram positive coccus. The strain of streptococcus pyrogenes will produce an exotoxin called erythrogenic toxin or pyrogenic toxin when it is infected by a certain bacteriophage. Scarlet fever is cause by the pyrogenic toxin, with exotoxin A that is most common. The bacteriophage T12 carries the exotoxin A and integrates into the streptococcal genome.

This infection is contracted by aerosol, inhalation of the bacteria from respiratory droplets of infected child. Another route of infection is by close skin contact. It is not a food borne or feco-oral disease.

This bacteria is also the culprit for rheumatic fever and ordinary streptococcal sore throat, but they produce different toxins.

In some children, they are labelled as asymptomatic carriers where the streptococcus pyrogenes is found in the upper respiratory tract; nose, ear and throat of the children but do not cause any symptoms.

By 10 years old, most children are protected by the acquired antibodies, which is why Scarlet fever is more common in the young children age less than 10.

Video of Scarlet Fever


Symptoms of Scarlet fever

In most cases, Scarlet fever starts with a high grade fever with chills and moderate to severe sore throat. Most fever peaks at the 2nd day and last for another two to three days. At the course of time, most will feel lethargic, fatigue, generalised muscle ache and fever. Some will have abdominal pain, nausea and vomiting. The cervical lymph nodes, which are at the neck region, can be enlarged and painful. In a small number of patient, Scarlet fever do not start with sore throat but starts with an infected skin wound.

After 2-3 days, a very distinguish rash that usually begins at the chest and back will appear. Then, the rash will spread to the upper limbs and lower limbs in a couple of days. The face will also look flushed with red cheeks. This rash appears blotchy red and generalised small elevations are felt on it, or felt like a rough patch, known as maculopapular patch. The skin has a feel similar to sand paper when touched.  When pressed with pressure, the skin blanches, where it turns pale and the colour returns when the pressure is lifted.  For most children, the rash does not itch.

After a week, the rashes will slowly disappear and then there could be peeling of the skin on fingers and toes, armpits and groin area called desquamation.

Pastialines, can be seen at the armpits, inguinal region or at the antecubital area. These lines are due to the hyperpigmentation of the skin; often appear at the same time as the maculopapular rash. In some, the capillary is fragile and may even rupture.

There can also have an appearance of very bright red tongue or known as strawberry tongue. The tongue is coated by a layer of white membrane with red edematous papillae, similar to the bright red colour of strawberries. There could also be forchheimer spots, which is small red spots that appears on the soft palate. The pharynx (back of the throat) and the tonsils will looks inflamed red or sometimes have exudates or pus.


Diagnosis and Investigation of Scarlet fever

Clinical Diagnosis

The diagnosis of Scarlet fever can be made clinically, by the description of symptoms and the clinical examination of the rash, throat and lymph nodes.


Throat swab

A throat swab is usually done and sent for rapid test for the presence of streptococcus. It is important to swab only the posterior pharynx and tonsils, avoiding other structures in the mouth. This test is very sensitive for Scarlet fever when done correctly.

If the rapid test is positive or highly suspicious for Scarlet fever, the throat swab will be sent for a culture as it could isolate the culprit bacteria. A rapid test takes minutes to be complete but a throat swab culture takes at least 48 hours for growth.


Full Blood Count

The test will show an elevation of total white cells with predominance of neutrophils. At 2nd week, there could be an elevation of eosinophils in some patients.


Antistreptolysin O titre

This is a blood test to check the titre of antistreptolysin O antibody which is produced against streptolysin O, a oxygen labile haemolytic toxin. A raised level indicates a present or past infection of group A streptococcus. A raised of titre in paired blood samples are more significant as the antibodies rise after 1-3 weeks and peak at the fifth week.

When evaluated together with clinical diagnosis, this is an excellent test for Scarlet fever and Rheumatic fever.


Blood culture

It is not a common investigation to do a blood culture, but it is usually done in severe infection or when the diagnosis is unclear. In some cases where the infection is so severe that the bacteria enters the blood stream, which is sterile in healthy humans.  When the blood culture grows bacteria, it is called group A streptococcus bacteremia.


Urine FEME

This examination is to watch out for proteins in the urine which is seen in glomerulonephritis, a complication of Scarlet fever.



Treatment of Scarlet fever

It is very important to be well rested for a speedy recovery. A couple days of bed rest, adequate amount of oral fluids and oral antibiotics will be sufficient. Paracetamols are excellent to reduce the fever and sore throat.

If detected and diagnoses early, Scarlet fever is easily treatable with oral antibiotics as outpatient. If the infection has spread with complications, hospital admission is required for close monitoring and intravenous antibiotics.

The goal of treatment is to shorten the duration of the illness, to minimize the spread of streptococcus, to prevent Rheumatic fever, glomerulonephritis and other complications.


Oral antibiotics

The oral antibiotics used are the same as those used to treat streptococcal sore throat. As most streptococcus is sensitive to beta-lactam antibiotics, oral penicillin or amoxicillin is the drug of choice with the duration of 10 days. Early start of antibiotics is very effective and prevents complications from taking place. It is important to remember that some streptococci are resistant to penicillin, thus needing macrolides or cephalosporins.

If one is allergic to penicillin, macrolides such as erythromycin can be taken. Clarithomycin and Clindamycin are also often used. A shorter course of Azithromycin for 5 days has gain popularity and is very effective.


Intravenous antibiotics

When there is a distant spread of infection with complications, intravenous antibiotics are indicated to prevent severe outcomes. Intravenous antibiotics that could be used are penicillin, cephalosporin and macrolides. It is important to check for sensitivity and resistance of streptococcus to the selected antibiotics to ensure efficacy.



If there is peritonsillar abscess, surgical drainage is indicated to prevent further complications. A more aggressive intravenous antibiotic is indicated for these patients.



There is no role for prophylaxis of Scarlet fever. For individuals that have close contact or exposure to Scarlet fever, it is important to be watchful for symptoms. If there is any symptom of Scarlet fever, medical treatment should be sought immediately. This is especially in young children, less than 5 years old. Most adult will not be affected.



Currently, there are no vaccines available for protection against streptococcus pyogenes. There have been many attempts to develop the vaccine but all have failed. The difficulty to produce a vaccine is due to the huge variety of streptococcus pyogenes strains that is not possible to vaccinate a population.



Prevention of Scarlet fever

Since Scarlet fever is spread by the inhalation of respiratory droplets, it is important to avoid a close contact with the infected patient. Wearing a face mask could protect the respiratory droplets at a length.

Frequent hand washing and hygiene help to prevent contamination of daily used items. This is a great step to prevent a spread of Scarlet fever. It is also important not to share towels, linens, utensils and personal items to prevent a spread.

If infected, there should be a home quarantine where the infected person should not go to work, school or any public places to avoid the spread. However, most patients are not contagious after 24 hours on antibiotics treatment.



Complication of Scarlet fever

Most of the patients respond very well to antibiotics to achieve full recovery with no residual infection. However, some do not progress well to respond to the antibiotics. In these cases, severe complications can occur and even be life threatening.

The most common complication is sepsis, or bacteremia where the bacteria enters the sterile blood stream. Patient could go into septic shock and most would need an intensive care unit admission. Further complication from that will be a meningitis or brain abscess that has high morbidity and mortality rate. Although it is rare, intracranial venous sinus thrombosis could happen.

Not uncommon, pneumonia and empyema occur as a distant spread of streptococcus pyogenes.  Osteomyelitis or septic arthritis is rare but is seen in late treatment cases.


Toxin mediated

Toxin mediated complication that could happen is myocarditis and toxic shock like syndrome. This is common in children and could be lethal if not treated appropriately. Myocarditis and toxic shock like syndrome is the common cause for mortality in Scarlet fever.


Immune mediated

Immune mediated complications are erythema nodosum, Rheumatic fever and glomerulonephritis.  Glomerulonephritis and Rheumatic fever is a chronic disease that causes prolonged stay in hospital and lifelong follow up in medical care. With the effective treatment and eradication of Scarlet fever in developed nation, the incidence of Rheumatic fever and glomerulonephritis has decreased markedly.


Local spread

The local spread of the bacteria from the upper respiratory tract to the local surrounding tissues can cause pus pockets to form, called peritonsillar abscess.  A more distant spread causes mastoiditis, sinusitis and otitis media.




Scarlet fever is a common infection for children with excellent outcome when treated early with antibiotics. It is important to recognise the symptoms and proceed to seek early medical care to prevent complications.




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The Team Manager Web Diseases




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