What is scarlet fever?

Scarlet fever is a bacterial infection characterised by a rough, red rash that starts on one part of the body and then spreads to other areas. Other symptoms include fever, itchiness, flushing in the face and a red, swollen tongue. Although scarlet fever can affect anyone, it most commonly occurs in children between two and 10 years of age.

In most cases, scarlet fever follows a sore throat (streptococcal sore throat) or school sores (impetigo). These conditions are all caused by group A Streptococcus bacteria. A toxin produced by these bacteria circulates in the blood to cause the characteristic rash of scarlet fever.

Droplets of body fluid containing group A Streptococcus bacteria are spread from one person to another by coughing, sneezing or sharing food, drinks and personal items. For this reason, the condition often spreads in crowded environments, such as day care centres and schools. Symptoms usually appear within one to four days of coming into contact with an infected person.

In the past, scarlet fever was considered to be a serious childhood disease. However, it is now easily treated with antibiotics. Once the infection has cleared, immunity develops and it is rare for scarlet fever to return.

Signs and symptoms

Symptoms of scarlet fever appear within about four days of coming into contact with an infected person, usually starting with a sore throat, headache and fever.

About 12 to 48 hours later, the characteristic rash begins to show. A few spots generally appear in one place, before turning into a rough, pink-to-red rash that looks like sunburn and feels like sandpaper. The rash rapidly spreads to other areas such as the neck, chest, ears, thighs and groin. Although the cheeks may become flushed, the rash doesn't usually spread to the face.

Other signs and symptoms of scarlet fever include:

  • Reduced hunger;
  • Redness, swelling or white patches inside the throat;
  • Swollen lymph nodes in the neck;
  • Nausea or vomiting;
  • Redness in the skin folds (Pastia lines);
  • Paleness around the mouth;
  • A white coating on the tongue that peels, then becomes red and swollen (also known as 'strawberry tongue'), and;
  • A general feeling of being unwell.

In most cases, the rash fades within about a week, but the skin may continue to peel for a number of weeks, particularly on the hands and feet.

Strawberry tongue, red and swollen tongue, sore throat with red swollen tongue.Development of the strawberry tongue associated with scarlet fever. 

Lymph nodes

A small organ of the lymphatic system containing many immune cells. Lymph nodes, also known as lymph glands, are the sites where many interactions between immune cells and foreign materials occur.

Causes

Scarlet fever is caused by group A Streptococcus bacteria that live in the nose and throat. This group is also known as group A beta-haemolytic streptococcus (GABHS) or Streptococcus pyogenes. The condition is spread by breathing in droplets of fluid that have been sneezed or coughed out by an infected person. Similarly, the bacteria can be passed on by touching the skin of someone with group A Streptococcus infection, or by sharing contaminated towels, bed linen or clothing.

Group A Streptococcus bacteria produce a harmful substance called erythrogenic toxin. This toxin travels around the body in the blood, triggering the release of natural inflammatory chemicals. The characteristic skin rash and red tongue of scarlet fever are the result of general inflammation and a widening of the blood vessels (vasodilation).

However, not everyone is prone to scarlet fever. For example, if two children from the same family become infected with group A Streptococcus bacteria, it is possible that only one (or neither) will develop scarlet fever. This also means that some children can carry the bacteria and pass on scarlet fever without developing any symptoms themselves.

Risk factors

Risk factors that increase the likelihood of developing scarlet fever include:

  • Age - being between the ages of two and 10 years;
  • An untreated streptococcal sore throat infection or school sores;
  • Exposure to a family or household member who has a streptococcal infection;
  • Crowded conditions, such as a day care centre or school, and;
  • Being prone to having Streptococcus bacteria living in your throat.

Methods for diagnosis

Scarlet fever is usually diagnosed by looking at symptoms, particularly if a rash is present. Your doctor may also look closely at the throat and glands.

A throat culture may also be performed to look for Streptococcus bacteria. During this procedure, the throat and tonsils are gently rubbed with a sterile cotton swab. This swab is then processed to confirm the diagnosis. In some cases, a blood sample may also be collected to rule out other potential causes of rash and sore throat.

Types of treatment

Treatments for scarlet fever aim to shorten the illness, limit the spread of infection and reduce the risk of complications. Your options include:

Self care

To relieve pain and fever, your doctor may suggest over-the-counter medications, such as paracetamol and ibuprofen. Similarly, calamine lotion or an over-the-counter oral antihistamine medication may be recommended to reduce itching.

For an associated sore throat, saltwater gargles, soothing liquids or medicated lozenges that cool or numb the throat may be helpful. Plenty of water and rest can help the immune system to naturally fight the bacterial infection.

Medications

Although the symptoms of scarlet fever are usually mild and will clear on their own within 7-10 days, Streptococcus bacteria are likely to remain if the infection is not treated. To reduce the risk of complications or further spread of infection, antibiotics are prescribed when Streptococcus bacteria infection has been confirmed.

The most common antibiotics for scarlet fever are oral penicillin or amoxicillin over a course of 10 days. Less frequently, erythromycin may be prescribed if an allergy to penicillin exists. Once treatment begins, symptoms generally start to ease within a day or two. Children can usually return to school 24 hours after starting antibiotic treatment.

Antihistamine

A substance that counters the physiological effects of histamine, a type of compound released by the tissues as an inflammatory response to an allergic reaction.

Immune system

The organs and cells involved in protecting the body against infection.

Complications

Although most cases of scarlet fever are successfully cured with antibiotics, complications can arise when the condition is left untreated. Possible complications include:

Spread of infection

If left untreated, Streptococcus infection can spread to the following areas:

Some signs that the infection has spread include fever, increased heart rate, rapid breathing, vomiting and confusion. Seek urgent medical attention if any of these symptoms occur.

Rheumatic fever

In rare cases, group A Streptococcus bacteria can cause ongoing activation of the body's immune system, weeks after scarlet fever has cleared. This subsequent condition, known as rheumatic fever, leads to inflammation in other areas of the body, including the joints, skin, heart and brain. Rheumatic fever often causes lasting damage to the heart valves (endocarditis), but not to other affected areas of the body.

Kidney disease

In a similar way to rheumatic fever, an ongoing immune response to group A Streptococcus bacteria can lead to inflammation of the kidneys, known as post-streptococcal glomerulonephritis. Again, it generally occurs a few weeks after scarlet fever has cleared.

Symptoms of post-streptococcal glomerulonephritis include blood in the urine, a puffy face and swollen feet and ankles. However, it usually clears on its own within a week without causing any lasting damage. For this reason, this condition is considered less serious than rheumatic fever, even though it occurs more frequently.

Toxic shock syndrome

In rare cases, the toxin produced by group A Streptococcus bacteria can cause a condition known as toxic shock syndrome, or TSS. This state of 'shock' is characterised by a sudden fever and extreme drop in blood pressure (hypotension). These symptoms may occur together with dizziness, confusion, vomiting or diarrhoea. If left untreated, the toxins may also damage the skin and organs. However, there is a good chance of recovery if the condition is diagnosed and treated early.

Immune system

The organs and cells involved in protecting the body against infection.

Osteomyelitis

Infection of the bone or bone marrow. It is usually caused by bacteria and can occur because of trauma to the bones, surgery or from infections in other parts of the body.

Prognosis

The outlook for scarlet fever is usually very good, particularly when the condition is correctly diagnosed and treated early with antibiotics. In most cases, the condition clears within about a week of starting treatment and complications are rare. Scarlet fever is usually contagious in the two days before symptoms appear, up until one or two days into treatment.

Even when left untreated, the fever usually ends quite suddenly after about five days. The rash generally fades and then begins to peel about a week later. However, it may take several more weeks for the throat to return to normal, during which time it is still possible to pass on the infection.

Prevention

Scarlet fever may be prevented by avoiding contact with people who have a sore throat or skin infection caused by group A Streptococcus bacteria. If contact cannot be avoided, the likelihood of developing scarlet fever may be reduced by maintaining good hygiene measures.

Teaching children good habits, such as washing hands and covering their mouths with a tissue or the inside of the elbow when coughing or sneezing, can also help to prevent the spread of infection. Keeping children with scarlet fever away from organised activities, such as childcare or school, is usually recommended until they are no longer contagious.

Replacing toothbrushes after starting antibiotic treatment can also reduce the possibility of reinfection of the throat. Similarly, taking the full course of antibiotics prescribed by your doctor may help to limit further spread of Streptococcus bacteria.