• Viral infections are extremely common in paediatrics and often present with rashes that can appear to be very alarming to parents / carers. It is useful to be able to identify an illness correctly from the exanthem (rash) to help inform your management plan and advice to parents.
• The history from parents and carers about the time course and progression of a new rash (where it starts, how it spreads) is critical and will give you vital clinical clues about what the rash might be.
• Associated symptoms can also give you a clue. For example, some rashes are associated with fever and malaise. Pay attention to the timing of the onset of the rash in relation to the fever.

Primary varicella zoster/ Chickenpox

Polymorphous appearance of rash in different stages on the back.

Polymorphous appearance of rash in different stages: macules -> papules -> vesicles -> ulcers -> scabs

• It is caused by varicella zoster virus.
• It is a self-limiting disease in immunocompetent children.
• The incubation period is around 14-21 days. A child is infectious 48 hours pre-rash, to 5 days after the onset of the rash
• The morphology of the typical chicken pox lesion is described as a “dew drop on a rose petal”.
• Chickenpox rash starts as small, red papules. The papules evolve into vesicles, which then rupture to form scabs.
• The rash often first develops in the upper trunk, head and neck.
• Repeated crops of new lesions keep appearing for 4-5 days. You can have different stages of rash appearances at the same time.
• Clinical features include fever, itchy vesicular rash which crops for up to 7 days.
• Watch for child with chickenpox whose fever initially settles, but then recurs a few days later – this pattern of history is likely suggestive of secondary bacterial infection.
• Complications of primary chickenpox include secondary bacterial and bloodstream (sepsis) infections, pneumonia, encephalitis and severe disseminated disease in the immunosuppressed group.
• Children with eczema can be severely affected (due to the underlying skin barrier defect).
• Treatment is mostly supportive. The use of calamine lotion or menthol 1% can be soothing for skin.
• Vaccines are available.
• Zoster Immunoglobulin (ZIG) – passive immunisation is given to:
  • Immunocompromised children exposed to VZV, e.g. stem cell transplant patients, congenital immunodeficiency, on immunosuppressives or high dose steroids in the previous 3 months
  • Neonates

Measles

Morbiliform/ maculopapular rash, typical in measles.

Kpoplik’s spot – pathognomical for measles, is usually seen on the buccal mucosa, opposite the molars. 

• It is caused by highly infectious measles virus, which belongs to morbillivirus family.
• The incidence has drastically decreased since the introduction of routine childhood immunisations.
• The incubation period is around 7-14 days. A child is infectious from pre-eruptive stage until 1 week after the onset of the rash.
• Clinical features include high grade fever, 3Cs (conjunctivitis, cough, coryza), malaise and typical maculopapular/ morbilliform rash.
• Koplik’s spot is pathognomic but only present in about 20-40% of cases.
• The rash tends to spread cephalocaudally. It usually starts behind the ears, then spread downward to the whole body. The rash can become confluent and it may desquamate in the second week.
• Older children and adults tend to have more severe disease than the very young ones.
• Complications include pneumonia, secondary bacterial infection, otitis media, encephalitis, subacute sclerosing panencephalitis (SSPE), hepatitis and rarely myocarditis.
• There is no effective treatment to date. Prevent is dependent on vaccination (herd immunity).

Rubella

Generalised maculopapular rash on the back.

Forchheimer spots, on the soft palate.

• It is generally a mild disease in childhood. However, it can cause severe insult in utero if pregnant women develop primary rubella infection during pregnancy.
• Rubella spreads via respiratory droplets.
• The incubation period is around 14-21 days. A child is infectious for around 7 days from the onset of rash.
• Clinical features include fever, generalised maculopapular rash, lymphadenopathy and sometimes Forchheimer spots (petechia on the palate).
• Complications include arthritis, encephalitis, thrombocytopenia, myocarditis and persistent ductus arteriosus (PDA).
• There is no effective treatment. Prevention is dependent on vaccination.

Roseola/ Exanthema subitum

Generalised macular rash on the torso of an infant.

• It is caused by human herpes viruses (HHV 6 and 7), although HHV 6 is more prevalent.
• The viruses are mostly transmitted through respiratory droplets.
• The incubation period is around 9-10 days
• It is characterized by high grade fever and malaise for a few days, followed by generalized macular rash. The rash usually appears as the fever goes away.
• It is commonly misdiagnosed as measles, rubella or allergic drug reaction.
• Rarely, roseola can cause aseptic meningitis, encephalitis, and hepatitis.

Erythema infectiosum/ Fifth disease

Lacy-like/ reticulate rash.

Lacy-like/ reticulate rash.

• It is caused by human Parvovirus B19.
• It spreads mostly via respiratory secretions. However, it can also transmit by vertical transmission in utero and by blood transfusion.
• The incubation period is around 14-21 days. A child usually presents with fever, malaise and myalgia. After 1 week they start to develop macular erythema over the trunk and limbs with central clearing of the lesions, resulting in a lacy pattern which may recur over weeks.
• Parvovirus B19 affects red cell precursors in the bone marrow, therefore the affected children can develop aplastic crisis especially in those with chronic haemoglobinopathies (e.g. sickle cell).
• In foetuses, it can cause cardiac failure, leading to hydrops fetalis due to profound anaemia.
• Erythema infectiosum usually starts with fever and malaise, followed by characteristic rash on the face (slapped cheeks) which then progresses into maculopapular, “lace-like”/ reticulate rash on the trunk and limbs.
• Complications are rare in children. Arthritis may accompany the rash in adolescents.

Molluscum contagiosum

Pearly, flesh-coloured papules with central umbilication. They are usually multiple in number

• It is caused by poxvirus.
• The classical lesions are small, flesh-coloured, pearly papules with central umbilication.
• They can be single but are usually multiple.
• If the lesions have been picked, scratched or inflamed, it may be difficult to appreciate its typical diagnostic morphology.
• Children with eczema can be severely affected (due to the underlying skin barrier defect).
• The lesions tend to involute spontaneously within a year.
• Majority of the children do not need treatment.

School exclusion

• The table below delineates some of the common childhood illnesses and the duration for a child to be excluded from school:
• To stop sickness from spreading, it is important  for parents to keep their children at home when they are ill. How long they should be home depends on what illness the children have.

Written by Dr Stanley Leong

Senior Paediatric Registrar and Dermatology Registrar