Once again, UK hospitals received an alert from Public Health England about the rise in cases of suspected scarlet fever. What is the extent of the problem, and how good are we at diagnosing scarlet fever?
As of a few weeks ago, Public Health England had received 11981 notifications of scarlet fever in the winter season. (Ed. This post was written in 2017 – what has changed?) The average number in the previous five years has been 4480. 89% of these notifications were for children under ten years of age, and the median age was four years. The infection rate is highest in the 1-4-year-old age group.
What is scarlet fever?
Scarlet fever is an infection caused by Group A Strep (Strep pyogenes). Group A strep can colonise the throat or the skin, and we know that up to 20% of (healthy) children are already colonised. When Group A strep causes infection, the bacteria release an exotoxin which causes the rash and the fever. The primary site of infection is usually the throat.
It is very contagious and is easily spread through saliva or mucus, i.e. on toys at preschool. It can also be transmitted through respiratory droplets. The incubation period is 2-5 days.
What are the symptoms of scarlet fever?
The symptoms usually start with fever (over 38.3°C), sore throat, and general fatigue/headache/nausea. 12-48 hours later, a rash appears on the abdomen and then spreads to the neck and extremities.
Characteristic features of the rash are:
Rough texture (like sandpaper)
Worse in the skin folds e.g. groin, axilla, neck folds (Pastia’s lines)
Other symptoms include a white coating on the tongue, which then peels and leaves a ‘strawberry’ tongue; flushed red face but with peri-oral pallor; cervical lymphadenopathy.
Most symptoms resolve in a week. After the symptoms have resolved, it is common to get peeling skin on the fingertips.
You usually only get Scarlet Fever once in your life.
How do you confirm the diagnosis of Scarlet Fever?
The diagnosis is clinical.
A throat swab is not routinely recommended, although, during specific outbreaks, Public Health England might advise this.
If you aren’t going to treat the patient but think they do have Scarlet Fever (see the discussion below about the utility of antibiotics), you should consider sending a throat swab. Otherwise, they will need to be excluded from school for two weeks.
What is the treatment?
Most mild cases will clear on their own (with no treatment).
There are two reasons for treating scarlet fever with antibiotics – prevention of complications and prevention of transmission.
1. Prevent complications
Complications of Scarlet Fever are much the same as complications of strep tonsillitis. They are divided into suppurative and non-suppurative.
Suppurative complications occur due to the infection spreading and include: otitis media; mastoiditis; sinusitis; peritonsillar abscess; meningitis; endocarditis; retropharyngeal abscess; and invasive group A strep (IGAS).
Non-suppurative complications occur later and occur mainly in untreated patients. They are rheumatic fever and post-strep glomerulonephritis.
IGAS is not common in children, but those at increased risk are children with co-morbidities, immunocompromised children, and those with co-existing chickenpox.
RebelEM makes a great case for why treating strep throat with antibiotics is not helpful, and the same principles should apply to Scarlet Fever.
If you’re aiming for symptomatic relief – treating with antibiotics provides about 6-12 hours of improvement in the length of symptoms compared with a placebo. This doesn’t take into account treating with fluids and analgesia or even giving a one-off dose of steroid (to be carefully considered in kids).
If you’re treating to prevent suppurative complications – a large study (14610 patients) in adults showed that the rate of suppurative complications is 1% regardless of whether or not antibiotics were given.
If you’re treating to prevent non-suppurative complications (rheumatic fever or post-strep glomerulonephritis) – the incidence of rheumatic fever is so low (and, before you say it, the reduction in rheumatic fever, or strep, predated the introduction of antibiotics and is related more to sanitation) that we would have treated millions of strep patients to prevent one case of rheumatic fever.
2. Prevent transmission
Public Health England has noted an increase in notifications for IGAS this winter season too – 1162 notifications compared to an average of 669 from the previous five years. However, the IGAS risk is much higher in the older population (median age is 55 years old). There has not been a significant increase in IGAS notification in children under 10 years of age this year compared to previous years. One rationale for the Public Health England recommendations is to prevent transmission of Group A strep from children to vulnerable adults.
If you decide to treat, then treatment is with ten days of penicillin. Amoxicillin can be used if there is a concern about compliance. Use azithromycin for penicillin allergy.
The fever usually settles 24 hours after starting the antibiotics, but the treatment course should still be completed.
What is the exclusion period for Scarlet Fever?
Children should be excluded from school until they have had 24 hours of antibiotics. (see our list of exclusion periods for other illnesses here). If you decide not to treat, though, the exclusion period is two weeks (so you may wish to consider a throat swab for diagnostic help).
Scarlet Fever is a notifiable disease – so don’t forget to let Public Health England know.
References
Scarlet fever: FAQs, Public Health England
Group A Strep infections: seasonal activity 2017/2018: second report, Public Health England
Scarlet fever, NICE CKS
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