The start of 2018 has seen UK hospitals receiving 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 actually diagnosing scarlet fever?
As of a few weeks ago, Public Health England had received 11981 notifications of scarlet fever in the winter season. The average number in the previous five years has been 4480. 89% of these notifications were for children under 10 years of age and the median age was 4 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 the Group A strep causes infection, the bacteria releases 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 pre-school. It can also be transmitted through respiratory droplets. The incubation period is 2-5 days.
What are the symptoms?
The symptoms usually start with fever (over 38.3oC), 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: white coating on the tongue which then peels and leave 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 is diagnosis confirmed?
Diagnosis is clinical.
A throat swab is not routinely recommended, although during specific outbreaks Public Health England might advice this.
If you aren’t going to treat the patient but you think they do have Scarlet Fever (see the discussion below about the utility of antibiotics) then 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; retropharygneal 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-morbities, immunocompromised children, and those with co-existing chicken pox.
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 treating for symptom relief – treating with antibiotics provides about 6-12 hours improvement in the length of symptoms when compared with 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 are 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 treat millions of strep patients to prevent one case of rheymatic fever.
2. Prevent transmission
Public Health England have 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 (media 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 are to prevent transmission of Group A strep from children to vulnerable adults.
If you do decide to treat, then treatment is with 10 days of penicillin. Amoxicillin can be used if there is a concern about compliance. Use azithromycin in 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?
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).
Of course, Scarlet Fever is a notifiable disease – so don’t forget to let Public Health England know.
Scarlet fever, NICE CKS