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Fever and a rash

Author: Hon A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand, May 2016.

Table of contents

Acute presentation of an unwell patient

Fever most commonly indicates bacterial or viral infection. If there is no systemic sepsis, localised rashes associated with infection tend to cause fewer systemic symptoms than generalised rashes associated with infection. Mucosal involvement is common. There are some acute auto-inflammatory disorders than mimic infection due to neutrophil activation, the neutrophilic dermatoses.

 Consider performing the following tests:

  • Swab for bacterial and viral culture if blisters, erosions, pustules or crusts
  • Blood culture if high fever
  • CBC, CRP
  • Coagulation screen if purpura or very sick patient
  • PCR and serology for specific bacteria or viruses
  • Echocardiography if septic emboli suspected
  • Skin biopsy of fresh skin lesions for histology, culture

Treatment depends on the cause. Consider referral to the emergency department if you are suspicious of a serious infection or the patient is very unwell.  

Differential diagnosis


  • Is the rash localised or generalised? What is its distribution? Are mucosal sites involved?
  • The severity of symptoms
  • Predominant morphology: is/are there erythema, blisters/erosions, pustules/crusts, purple/black areas? 

Fever and localised rash

Painful red, hot skin

  • Cellulitis
    • Unilateral swelling/induration
    • Spreads over hours to days      
    • May have associated wound or skin disease

  • Erysipelas 
    • Unilateral large plaques with sharp, stepped edge
    • Large blisters
    • Face, lower legs or anywhere
    • Spreads over hours to days
    • May have associated lymphangitis (red streak to local lymph nodes)
    • Culture Streptococcus pyogenes

  • Panniculitis – other 
    • Many causes
    • Often associated with underlying disease

Prominent blisters/erosions

  • Hand, foot and mouth 
    • Mainly young children
    • Symmetrical vesicles mainly hands, feet and mouth
    • Can extend to limbs and buttocks
    • Culture/PCR enterovirus

  • Herpes simplex
    • Monomorphic, umbilicated vesicles, erosions, crust
    • Culture/PCR Herpes simplex

  • Herpes zoster 
    • Dermatomal
    • Painful
    • Monomorphic vesicles (early), erosions, crust and ulceration (late)
    • Culture/PCR Herpes varicella-zoster


Purple/black areas

  • Necrotising spider bite 
    • Endemic venomous spiders
    • Spider must be observed to make this diagnosis
    • Central punctum with purpura/necrosis, surrounding erythema and induration

Katipo spider bite

Fever and generalised rash


  • Kawasaki disease 
    • Young child with red skin and mucosal surfaces
    • Swollen hands and feet
    • Peeling is a late feature
    • Lymphadenopathy
    • Cardiac artery aneurysms
    • Other organ involvement leads to a variety of signs
    • No specific diagnostic test

  • Measles 
    • Red eyes, red tongue, Koplik spots
    • Coryza, cough
    • Rash has bronze hue
    • Serology/RT-PCR measles

  • Roseola / erythema subitum
    • Infant
    • High fever + upper respiratory symptoms
    • Rash is brief
    • Serology for herpes virus 6 and 7 is not generally available
  • Scarlet fever (Streptococcus pyogenes
    • Strawberry tongue
    • Scarlatiniform rash: tiny red macules or rough papules
    • Swollen then peeling hands
    • Evidence of streptococcal infection


  • Acute febrile neutrophilic dermatosis 
    • Neck, limbs, upper trunk
    • Pseudovesicular plaques, blisters, pustules, purpura, or ulceration
    • Disease associations: rheumatoid arthritis, inflammatory bowel disease, autoimmune arthritis, myeloid dysplasia
    • Biopsy suggestive (neutrophils)


 May involve mucosal surfaces

  • Eczema herpeticum 
    • Prior eczema or rarely, other skin disease
    • Clustered monomorphic, umbilicated vesicles, pustules or crusts
    • Culture/PCR Herpes simplex

  • Generalised pustular psoriasis (Zombusch) 
    • May or may not have history of plaque psoriasis
    • Symmetrical eruption of numerous superficial pustules on red skin
    • Often annular, flexural
    • Associated with hypocalcaemia
    • Biopsy suggestive

  • Varicella (late stage) 
    • More itch than pain
    • Mainly scalp, face, trunk
    • Culture/PCR Herpes varicella zoster

Widespread purple/black areas

  • Vasculitis 
    • Palpable purpura
    • Recent infection or drug or underlying chronic disease
    • Biopsy confirmatory       



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