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Scarlet fever is a bacterial infection caused by group A streptococcus bacteria. In the UK, the incidence of scarlet fever has been increasing in recent years, with outbreaks occurring every few years.
Though scarlet fever is considered to be a seasonal illness with its peak between December and March, there was a higher-than-expected prevalence during the first part of summer 2022, leading to exceptional levels of the disease. In 2023, the weekly rates of notifications from GP consultations have so far been at the top end of normal.
What is scarlet fever?
Scarlet fever, also called scarlatina, is a bacterial infection caused by group A streptococcus bacteria. It is usually a mild illness. The bacteria produce a toxin that causes a red rash, which is how the infection got its name. Scarlet fever usually affects children, although it can occur in people of any age.
Group A strep is sometimes referred to as GAS. This infection tends to affect the skin and throat and it gets its name from the colour of the red rash that appears.
It’s possible for people to carry group A strep bacteria without having symptoms of illness themselves. Though most people who do get an infection have mild symptoms, the bacteria can lead to severe illnesses or life-threatening disease too.
Strep throat and scarlet fever are caused by the same group A streptococcus bacteria. The difference, however, is the presence of the rash.
Scarlet fever in the past
Scarlet fever was much more common and more dangerous before the advent of antibiotics. The disease saw lethal epidemics in the 19th century. In 1834, the fatality rate was around 15%. For most of the 1900s, this disease was the most common childhood illness to be fatal. Scarlet fever is believed to be to blame for Helen Keller’s loss of sight and hearing. It was also to blame for the deaths of Charles Darwin’s daughter and son in the 1850s.
Antibiotics changed the prognosis of the disease for many
In 1928, Alexander Fleming was researching antibacterial agents when he made an accidental discovery in a Petri dish. The Petri dish contained staphylococci but Fleming noticed a fungus on the plate, which had caused the bacteria in the surrounding areas to be lysed – in other words, they had broken down. Fleming named this substance penicillin due to the fungus being the Penicillium fungus.
Significant progress towards an effective treatment was made a number of years later in 1939 when Howard Walter Florey and Ernst Boris Chain managed to establish fermentation conditions on a scale large enough to produce antibiotics. As a result, Fleming, Chain and Florey were all awarded the 1945 Nobel Prize in physiology or medicine.
Unlike other bacteria, Streptococcus pyogenes is still sensitive to penicillin and has not evolved to become resistant.
What are the symptoms of scarlet fever?
For most people, scarlet fever is a mild illness but it can be painful.
- Sore throat – The tonsils are usually enlarged and red. The throat itself is often red and there are often red spots on the roof of the mouth.
- Fever (this is usually over 39°C (102.2°F)).
- Swollen and tender lymph nodes in the neck (in up to 60% of cases).
- A red and swollen tongue – Often referred to as a strawberry tongue because of its appearance. In the first two days, this might have a white coating with protruding red papillae. After around four days, the coating comes off to reveal a bright red ‘strawberry tongue’.
- Abdominal pain.
- A red rash on the skin – This usually starts on the chest and spreads. It feels rough, like sandpaper. The rash has bumps that appear like goosebumps after the first day. The rash tends to disappear after a week but the skin often peels during healing. It can also feel itchy.
Variable symptom presentation
Children who are younger than five often have atypical scarlet fever presentations. Those who are less than three years old might just have a low-grade fever and nasal congestion. Babies might be more irritable and have a poor appetite.
Is scarlet fever contagious?
Scarlet fever is very contagious. It spreads easily when someone who is infected sneezes or coughs. The bacteria from the infection travel in droplets in the air. When someone else touches something the droplets land on and then touches their own mouth or nose, or if they inhale the droplets (aerosol transmission), they can develop scarlet fever. Droplets can also be transferred by sharing cups or plates with an infected person.
A person who is in close contact with someone infected with scarlet fever has a 35% chance of catching it. Only one in 10 children who are infected with the bacteria will develop scarlet fever.
Who is at risk of scarlet fever?
The most common age to get scarlet fever is between 4 and 8 years old. By the age of 10, the majority of children will have developed protective antibodies. Infants up to the age of two tend to still hold on to acquired maternal antibodies.
Both females and males are equally affected by the illness.
People who have a greater risk of this illness include:
- Those attending day care, going to boarding schools or military camps or other environments with a high concentration of people.
- Children above the age of three.
- People who have been in close contact with someone who has a skin or throat infection caused by strep A.
- Those who are at extremes of the age range, e.g. the very old or very young.
- Postpartum women.
- Those who are immunosuppressed or immunocompromised.
- Those with comorbidities like diabetes mellitus, skin breakdown or malignancy.
- Those with concurrent influenza or chickenpox.
- Those who are dependent on alcohol or who inject drugs.
How common is scarlet fever?
Scarlet fever is considered to be a rare illness, despite its recent rise in case numbers. This illness is a notifiable disease, which means that when it is diagnosed, GPs will record it for official statistics. There has been a rise in the number of cases since 2014 and there are usually between 15,000 and 30,000 cases diagnosed each year. Most of the people affected are school-age children up to the age of eight.
Occasionally, you’ll see outbreaks in nurseries and schools. According to NICE, an outbreak of scarlet fever is defined as ‘a credible report of two or more probable or confirmed scarlet fever cases attending the same school or nursery or other childcare setting, notified within 10 days of each other, with an epidemiological link between cases, for example they are in the same class or year group’.
Some children can carry the bacteria without showing any symptoms. If you’ve had scarlet fever once, you’re very unlikely to get it again.
Risk factors of scarlet fever
This is most commonly a childhood disease and, as such, children are most at risk. However, it is possible for other age groups to be affected.
For most people, scarlet fever is a mild illness. Some cases clear up on their own but it is always best to see a GP as getting treatment can speed up the recovery process and reduces the risk of having any complications. Having treatment also means the person becomes non-contagious sooner.
If complications do occur, they’re usually mild. However, there are more serious complications, which is why treatment with antibiotics is always recommended (and why you should always complete the course as prescribed).
Some possible mild complications include:
- Tonsil abscesses and infection (retropharyngeal abscess, peritonsillar abscess and peritonsillar cellulitis).
- Swollen lymph nodes.
- Sinusitis – Inflammation of the sinuses (and mastoiditis).
- Ear infections.
More serious complications include:
- Acute rheumatic fever – This is an immune response that can lead to endocarditis and carditis (and subsequently valvular heart disease). It can also cause reactive arthritis.
- Kidney disease (acute post-streptococcal glomerulonephritis) – This usually happens after two weeks of the initial infection. It often presents with reduced urine output, haematuria (blood in the urine), peripheral oedema (swelling of the extremities), proteinuria (protein in the urine) and hypertension (high blood pressure).
- Otitis media – Inflammation in the middle ear, associated with effusion.
- Streptococcal pneumonia – Inflammation of the lungs.
- Septicaemia – Blood poisoning that can lead to sepsis or septic shock.
- Cellulitis – Soft tissue or skin infection.
- Septic arthritis – Joint inflammation.
- Osteomyelitis – Inflammation or infection of the bone or bone marrow.
- Bacteraemia – A bloodstream infection.
- Meningitis and cerebral abscess.
- Necrotising fasciitis – A severe infection that involves areas of soft tissue dying under the skin.
- Streptococcal toxic shock syndrome – A rapidly progressive condition that combines low blood pressure with multiple organ failure.
- Endocarditis – An infection of the inner lining of the heart.
- Liver abscess.
Though complications are rare, they can lead to kidney damage, heart damage, liver damage, joint or bone problems and death. With severe infections, the risk of mortality is between 15% and 25%.
Scarlet fever risks in pregnancy
According to the NHS, there is no evidence to suggest that catching this disease when pregnant will put the baby at risk. That said, you should always inform midwives and doctors if you have been in contact with someone who has had scarlet fever.
Diagnosis of scarlet fever
Most of the time, a doctor will diagnose scarlet fever from the patient’s symptoms. This diagnosis can be confirmed by a throat swab to see if Group Strep A has caused the symptoms. The throat swab is sent to a laboratory to see if the bacteria is present. Sometimes, a blood test is needed to confirm the diagnosis.
If scarlet fever isn’t treated with antibiotics, it is infectious for two to three weeks from the onset of symptoms. If treatment is prescribed and taken, the patient is no longer contagious after 24 hours.
Scarlet fever can present in a similar way to Kawasaki disease. This has the red strawberry tongue but not the initial white tongue. Other symptoms to suggest Kawasaki disease include cracked lips, conjunctival redness and the child being younger than five.
Hand-foot-and-mouth disease can also present in a similar way.
Can scarlet fever be prevented?
The group A strep bacteria that causes scarlet fever is spread through contact with mucus from the throat or nose of an infected person. It can also be caught from a skin infection like impetigo. The only way to prevent catching scarlet fever is to practise good hygiene.
This means frequent handwashing, using alcohol-based hand sanitiser when handwashing isn’t possible, and coughing and sneezing into a tissue or the elbow if no tissue is to hand.
If someone is known to have scarlet fever, they should be isolated from others to help prevent the disease from spreading. They should use separate eating utensils and drinking utensils too.
Children who have symptoms or who have been diagnosed with scarlet fever should stay off school or day care until they have been on antibiotics for at least 24 hours and are feeling well enough.
Unfortunately, there is no vaccine to prevent scarlet fever.
Treatment for scarlet fever
The typical treatment for scarlet fever is a 10-day course of antibiotics. Once on antibiotics, the patient will usually find their fever subsides after 24 hours. However, because this is a disease that can have severe complications, it’s crucial to finish the course of antibiotics completely.
Normally, patients will be prescribed penicillin for 10 days. However, those who are allergic to penicillin can receive clarithromycin for 10 days (this is generally prescribed to young babies up to six months old), azithromycin for five days (this is prescribed to anyone aged over six months that isn’t pregnant or postpartum) or erythromycin for 10 days (this is for anyone who is pregnant or has had a baby in the last 28 days).
For those prescribed penicillin, this is usually needed four times a day. For clarithromycin, this is usually prescribed twice daily, and for erythromycin, this is usually four times a day.
Since this is a notifiable disease, GPs must complete a notification form within three days of seeing the patient.