Dermatology
Question 118 of 300
A 4 year old boy is brought to the Emergency Department with a 1 day history of rash following a sore throat. You diagnose scarlet fever. What is the recommended school exclusion period for scarlet fever?
Answer:
- Advise the person or family/carers on measures to reduce the risk of cross-infection:
- Exclusion from nursery, school, or work is needed for at least 24 hours after starting appropriate antibiotic treatment
- Effective and frequent handwashing is needed (for example before preparing and eating food, after using the toilet, after play, and after sneezing and disposing of tissues)
- Avoid sharing eating utensils and towels, and dispose of tissues promptly
- Avoid contact with people at high risk of complications of scarlet fever
Scarlet Fever
Dermatology
Last Updated: 12th February 2021
Scarlet fever is a notifiable infectious disease caused by the bacterium Streptococcus pyogenes, also known as group A streptococcus (GAS). When GAS cause infection, the primary site is usually the throat resulting in pharyngitis. The rash and fever associated with scarlet fever are due to exotoxin or superantigen release by the bacteria. Scarlet fever can occur at any age but is most common in children between 2–8 years of age (median age 4 years).
Transmission
- GAS bacteria can colonise the throat or skin. Asymptomatic pharyngeal carriage of S. pyogenes occurs in 3–26% of healthy children. The incubation period is usually 2–3 days but can range from 1–6 days.
- Scarlet fever is highly contagious and is transmitted when a person's mouth, throat, or nose comes into contact with infected saliva or mucus by aerosol transmission (by breathing infected airborne droplets produced through coughing or sneezing) or by direct contact with contaminated surfaces (including cups, utensils, taps, and handles).
- Outbreaks in nurseries, schools, and other institutions may occur where there is close contact between people.
- People can be infectious for 2–3 weeks after the onset of symptoms, unless they are treated.
Clinical features
- Initial clinical features may be non-specific and include:
- Sore throat
- Fever (typically greater than 38.3°C)
- Headache, fatigue, nausea, and vomiting
- A blanching rash usually develops on the trunk 12–48 hours after initial symptoms, before spreading to the rest of the body and flexures
- The rash is characteristically red, generalised and pinpoint (punctate) with a rough, sandpaper-like texture
- It may be accentuated in the skin folds of the neck, axillae, groin, elbows, and knees with a deep red, linear appearance (so-called 'Pastia's lines')
- The palms and soles are typically spared
- The skin may peel after the rash resolves, particularly at the tips of the fingers and toes, and less commonly on the trunk and limbs
- Examination may also reveal:
- Strawberry tongue — initially the tongue is covered with a white coat through which red papillae may be seen; later, the white covering disappears, leaving the tongue with a beefy red appearance
- Associated cervical lymphadenopathy
- Flushed face, with marked circumoral pallor
- Pharyngitis and small red spots (petechiae) on the hard and soft palate ('Forchheimer spots')
Differential diagnosis
- Rubella
- Parvovirus B19 infection
- Measles
- Roseola infantum (herpesvirus type 6)
- Enterovirus and adenovirus infections
- Kawasaki disease
- Staphylococcal toxic shock syndrome (TSS)
- Brucellosis, cytomegalovirus, toxoplasmosis, HIV, syphilis, and mononucleosis reaction to amoxicillin
- Other adverse drug reactions, echovirus, Coxsackievirus, and viral hepatitis
- Tropical viruses, including alphaviruses and flaviviruses (for example Dengue fever)
Investigations
Throat swabs and blood tests are not routinely indicated for the diagnosis of scarlet fever.
Consider taking a throat swab for culture of Group A streptococcus (GAS) (prior to starting treatment) if:
- There is uncertainty about the clinical diagnosis.
- A case is suspected to be part of an outbreak — the local health protection team should advise primary care if a local outbreak is suspected and when testing is appropriate.
- There is a true allergy to penicillin, to determine antimicrobial susceptibility, depending on clinical judgement.
- A case is in regular contact with vulnerable people who are at high risk of complications, such as healthcare workers.
Measurement of serum antistreptolysin O (ASO) antibody titres are not useful in acute infection, but may be helpful in the diagnosis of post infection complications, such as acute rheumatic fever or glomerulonephritis.
Management
- Notify the local health protection team promptly within 3 days by completing a notification form if a diagnosis of scarlet fever is suspected.
- Consider admission if a person has severe symptoms, a suspected serious or life-threatening complication or a high risk of developing complications.
- If the person does not need hospital admission, prescribe appropriate antibiotics promptly, regardless of the severity of illness. Prescribe phenoxymethylpenicillin (penicillin V) four times a day for 10 days first-line.
- Advise the person or family/carers about appropriate self-care measures e.g. paracetamol or ibuprofen for symptom relief, adequate rest, adequate fluid intake
- Advise the person or family/carers on measures to reduce the risk of cross-infection:
- Exclusion from nursery, school, or work is needed for at least 24 hours after starting appropriate antibiotic treatment
- Effective and frequent handwashing is needed (for example before preparing and eating food, after using the toilet, after play, and after sneezing and disposing of tissues)
- Avoid sharing eating utensils and towels, and dispose of tissues promptly
- Avoid contact with people at high risk of complications of scarlet fever
Complications
- Suppurative complications are due to local spread of the infection and tend to occur early in the course of infection, and include:
- Otitis media
- Throat infection and abscess (peritonsillar cellulitis, peritonsillar abscess, retropharyngeal abscess)
- Acute sinusitis and mastoiditis
- Non-suppurative (immune-mediated) complications tend to occur later in the course of infection, particularly in untreated people, and include:
- Acute rheumatic fever — this is an immunologically-mediated response and can cause carditis and endocarditis (leading to valvular heart disease) and reactive arthritis
- Acute post-streptococcal glomerulonephritis — this typically occurs 2 weeks or more after the acute initial infection, and may present with haematuria, reduced urine output, peripheral oedema, proteinuria, and hypertension
- Invasive Group A streptococcal (iGAS) infections may be life-threatening and include:
- Streptococcal pneumonia
- Meningitis and cerebral abscess
- Endocarditis, septic arthritis, and liver abscess
- Cellulitis, necrotising fasciitis, and streptococcal toxic shock syndrome
- Sepsis
- Risk of death
People who are at increased risk of invasive Group A Streptococcal infection (iGAS) and complications include people:
- At extremes of the age range, such as the very young and old, or postpartum women
- Who are immunocompromised or immunosuppressed
- With comorbidities such as skin breakdown, diabetes mellitus, or underlying malignancy
- With concurrent chickenpox or influenza
- Who inject drugs or are alcohol dependent
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
