Pyrexia of unknown origin (PUO) may be defined as any febrile illness (temperature greater than 38°C) lasting 3 weeks or longer, without any obvious cause and failure to reach a diagnosis despite one week of inpatient investigation. In these conditions there is thus a special need for a lab diagnosis to guide the choice of appropriate therapy. Fever ≥ 38.3°C (>101°F) on several occasions