Bacteraemia and occult bloodstream infection

Overview & Definition

Picture a 14-month-old brought in with two days of fever to 39.5 °C. She is alert, smiling, drinks from her cup, has a clear chest, no rash and no obvious focus. In the pre-pneumococcal-vaccine era, between roughly three and nine of every hundred children just like her had bacteria circulating in their bloodstream, and the worry was that pneumococcus might settle in her meninges before anyone realised. Today that number is a fraction of one per cent. The child has not changed; the population risk has. That shift is the single most important idea on this topic. [1] [9]

Bacteraemia is the presence of viable bacteria in the bloodstream, confirmed when a blood culture grows a pathogen. The word describes a laboratory and physiological fact, not a syndrome. A febrile child with bacteraemia may be in septic shock, may have an obvious pneumonia, or may look completely well — the same finding spans the whole spectrum of severity. [1] [12]

Occult bacteraemia is the historical name for the child at the well end of that spectrum: fever without an apparent focus in a child who does not look toxic, where bacteraemia is found only because a blood culture was drawn. It was a clinical problem worth chasing in the 1990s because occult pneumococcal bacteraemia carried a real risk of meningitis if the child was sent home untreated. With pneumococcal and Haemophilus influenzae type b conjugate vaccines, the prevalence fell so far that the question reframed: clinicians now ask whether the febrile child is at risk of a serious or invasive bacterial infection, and use validated pathways to decide who needs investigation and empiric treatment. [1] [3] [9]