At a Glance - Fifth disease (erythema infectiosum) vs scarlet fever

Fifth Disease (erythema infectiosum)



  •  Caused by human parvovirus B19.
  •  Most common in young children (3-15 years). About 60 per cent of adults are seropositive.
  •  Tends to occur in late winter and early spring.
  • Incubation period 4-14 days.


  • Mild prodromal headache, low grade fever, coryza. Patient may be unaware of these.
  • Onset of red cheeks; fades within 2-4 days. Nose, perioral and periorbital regions spared.
  • Followed by lacy, morbilliform rash, mainly on the limbs.
  • Rash may fade and recur over the following three weeks.
  • Adults, particularly women, may develop a polyarthropathy that may persist for months.
  • Complications in children are rare, but are more of a problem in adults, especially in pregnancy; for example, intrauterine death, hydrops fetalis, anaemias.

Red cheeks mark disease onset


  • Children - symptomatic treatment only while awaiting spontaneous resolution.
  • If diagnosis is doubtful or during pregnancy confirmation of the diagnosis will be important.
  • Pregnancy - refer women after exposure to the virus or with IgM antibodies to PV-B19 to obstetrician for assessment of possible complications.

Scarlet Fever


  • Rash caused by release of erythrogenic toxin from group A ss-haemolytic streptococcus.
  • Transmitted in respiratory droplets.
  • More common in children aged 4-8.
  • Most have acquired lifelong antibody protection by the age of 10.
  • Infants under the age of two are protected by maternal antibodies.
  • Incubation period 1-4 days.
  • School exclusion for 24 hours after initiation of antibiotics or until well enough.
  • Scarlet fever is a notifiable disease.


  • Sudden onset of fever, sore throat, headache and vomiting.
  • Erythematous rash with scarlet macules develops within 12-48 hours.
  • Rash spreads from face to the trunk and limbs.
  • Strawberry tongue - white-coated tongue with red papillae showing through.
  • After 4-5 days, raspberry tongue as white coating clears.
  • Rash fades after about a week and is followed by desquamation.

The rash fades after a week


  • Rheumatic fever, peritonsillar abscess, pneumonia, meningitis.
  • Antibiotics treatment reduces the risk of complications.


  • Throat swab to confirm group A ss-haemolytic streptococcus.
  • Antistreptolysin O test after the acute phase will confirm the diagnosis if the titre is high.


  • Drug of choice is phenoxymethylpenicillin V for 10 days.
  • Alternatives are erythromycin or a cephalosporin.

Contributed by Dr Jean Watkins, a sessional GP in Hampshire.

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