It mainly affects children. Left untreated, it can sometimes lead to severe complications.
In the past, it was a serious childhood illness, but modern antibiotics have made it much rarer and less threatening.
However, occasional and significant outbreaks still occur.
Here are some key points about scarlet fever. More detail is in the main article.
Scarlet fever can cause a distinctive rash, among other symptoms.
Image credit: Estreya, 2007.
Scarlet fever is caused by a toxin released by the bacteria Streptococcus pyogenes (S. pyrogenes), the same organism that causes strep throat.
Another term, scarlatina is often used interchangeably with scarlet fever, but scarlatina more commonly refers to a less acute form.
Early treatment with antibiotics can prevent complications.
Signs and symptoms generally appear about 1 to 4 days after initial infection. The first symptoms of scarlet fever are usually:
- a red, sore throat, sometimes with white or yellowish patches
- a fever of 101 Fahrenheit (38.3 Celsius) or higher, frequently with chills.
A rash appears 12 to 48 hours after these first symptoms.
Red blotches appear on the skin. These turn into a fine pink-red rash that looks like sunburn. The skin feels rough when touched, like sandpaper.
The rash spreads to the ears, neck, elbows, inner thighs and groin, chest, and other parts of the body.
It does not usually appear on the face, but the patient's cheeks will become flushed, and the area around the mouth becomes pale.
If a glass is pressed on the skin, the rash will turn white.
After about 6 days, the rash usually fades. In milder cases, the rash may be the only symptom.
Other possible symptoms include:
- difficulty swallowing
- feeling unwell
- nausea, vomiting, loss of appetite, and abdominal pain
- broken blood vessels in the folds of the body, for example, the armpits, groin, elbows, knees, and neck, known as Pastia's lines
- swollen neck glands, or lymph nodes, that are tender to the touch
- a white coating forms on the tongue that peels away, leaving a red and swollen "strawberry" tongue
If severe muscle aches, vomiting, or diarrhea occur, the doctor will need to rule out other possible causes, such as toxic shock syndrome (TSS).
The skin of the hands and feet will peel for up to 6 weeks after the rash has gone.
Scarlet fever is caused by the bacterium S. pyogenes, or group A beta-hemolytic streptococcus, the same bacterium that causes strep throat.
When the bacteria release toxins, scarlet fever symptoms occur.
How is it spread?
Scarlet fever can develop from strep throat.
Scarlet fever is passed on through fluids from the mouth and nose. When a person with scarlet fever coughs or sneezes, the bacteria become airborne in droplets of water.
Another person can catch it by inhaling these droplets or by touching something the droplets land on, such as a door handle, and then touching the nose and mouth.
Touching the skin of a person with a streptococcal skin infection can also spread infection. Sharing towels, baths, clothes, or bed linen with an infected person increases the risk.
A person with scarlet fever who is not treated may be contagious for several weeks, even after symptoms have gone.
Some individuals do not react to the toxin. They can carry and pass on the infection without showing any symptoms. Only those who react to the toxin will develop symptoms.
This makes it hard for someone to know if they have been exposed.
Less commonly, infection may occur through touching or consuming contaminated food, especially milk.
The bacteria can spread more easily among people in close contact, for instance at school, home, or work.
A doctor can normally diagnose scarlet fever by looking at the signs and symptoms.
A throat swab may help determine which bacteria caused the infection. Sometimes a blood test is also ordered.
Most mild cases of scarlet fever resolve themselves within a week without treatment.
However, treatment is important, as this will accelerate recovery and reduce the risk of complications.
Treatment normally involves a 10-day course of oral antibiotics, usually penicillin.
The fever will usually go within 12 to 24 hours of taking the first antibiotic medication, and patients normally recover 4 to 5 days after starting the treatment.
Patients who are allergic to penicillin may take erythromycin or another antibiotic instead.
It is important to take the full course of antibiotics, even if symptoms go away before it is finished. This is necessary to get rid of the infection and reduce the risk of post-strep disorders developing.
If the patient does not start feeling better within 24 to 48 hours after starting the antibiotic treatment, they should contact a doctor.
The patient is no longer contagious 24 hours after antibiotics begin, but they should stay at home for the full course of antibiotics.
Managing symptoms at home
When following up the antibiotic treatment, other strategies can help relieve symptoms.
It is important to drink plenty of liquids, especially if there is no appetite. The environment should be kept cool.
Tylenol, or acetaminophen, may help relieve aches and pains, and reduce the fever.
Calamine lotion can help reduce itching.
Pneumonia is a potential complication of scarlet fever.
Most people will not experience complications, but the following can occur:
- ear infection, including otitis media
- throat abscess
- inflammation of the kidneys, due to an immune response to strep bacteria, and possibly long-term kidney disease
- rheumatic fever
- skin infections
The following complications are possible but very rare:
- acute kidney failure
- meningitis, an inflammation of the membranes surrounding the brain and spinal cord
- necrotizing fasciitis, a serious flesh-eating disease
- toxic shock syndrome
- endocarditis, an infection of the heart's inner lining
- infection of the bone and bone marrow, known as osteomyelitis
Another risk is known as pediatric autoimmune neuropsychiatric disorders associated with streptococcal (PANDAS) infections.
Some research has indicated that strep bacterial infection may trigger an autoimmune response that worsens symptoms of certain childhood disorders.
The increase in symptoms usually passes after a few weeks or months.
The best ways to prevent transmission of scarlet fever and other infectious diseases are:
- isolation, or staying away from other people, including not attending school
- washing or disposing of used handkerchiefs or tissues immediately, and washing the hands thoroughly with warm water and soap
- thorough and frequent handwashing with warm water and soap
- not sharing drinking glasses or eating utensils
- covering the nose and mouth when coughing and sneezing, by using a handkerchief or coughing or sneezing into the inside of the elbow