Persistent fever and rash in a young child

A 22 month old white Australian boy presented to his general practitioner with irritability, red eyes, and a two day history of high fever (highest at 41°C) that did not respond to paracetamol and ibuprofen. He had no history of cough, coryza, or rash. His medical history was unremarkable and immunisations were up to date. On examination, he had bilateral non-exudative conjunctival injection and was diagnosed with a non-specific febrile illness with associated conjunctivitis. His family then took him on a planned family holiday to Thailand where his conjunctivitis improved, but the fevers continued unabated. In addition to the fevers, his parents noted a mild nappy rash. On day 8 of the illness, his parents took him to a local clinic after a couple of episodes of diarrhoea. He was diagnosed with gastroenteritis. Later that day he became more unwell with increasing irritability and a progressive rash so his parents took him to hospital. He was dehydrated and lethargic and physical examination showed cervical lymphadenopathy, fissured lips, and an injected pharynx. His hands and feet were oedematous and his legs were covered in a pink maculopapular rash. Blood tests showed leucocytosis and increased acute phase reactants, but other haematological markers were normal. A chest radiograph was normal. He was admitted with presumed bacterial sepsis and started on broad spectrum intravenous antibiotics. However, after two days of antibiotics, his symptoms did not improve.