Bacteraemia and occult bloodstream infection — formative SAQs

SAQ 1 (10 marks, 15 minutes)

Stem. A 14-month-old, fully immunised boy is brought to the emergency department with two days of fever to 39.5 °C. He is alert, smiling, drinks from his cup, has a clear chest, no rash, normal perfusion and no identifiable focus. His immunisations are up to date, including pneumococcal conjugate vaccine. Outline your assessment, the investigation you would and would not perform, and the safety-net you would give. [9]

Model answer — SAQ 1

The priority is to recognise that this is a well-appearing vaccinated child in the post-conjugate-vaccine era, where the prevalence of occult bacteraemia has fallen to well below one per cent. The clinical question is no longer "is the blood culture going to be positive?" but "is this child at risk of invasive bacterial infection, and can I safely defer empiric antibiotics?" [1] [9]

I would state the appearance explicitly — alert, interactive, normal colour, tone and perfusion, drinking well — because appearance is the single most powerful bedside discriminator. I would measure age-adjusted observations and perform a focused focus search: ears, throat, chest, abdomen, skin, joints and central nervous system. A urine test (clean catch or catheter) is reasonable in this age group for an unexplained fever, because urinary tract infection is the commonest serious bacterial infection in febrile infants. [1] [3]

I would not routinely perform a blood culture or give empirical ceftriaxone, because routine expectant observation was justified in the pre-vaccine era when occult pneumococcal bacteraemia carried a real risk of meningitis, and that prevalence has collapsed with conjugate vaccines. I would reserve blood culture and inflammatory markers for higher-risk features: a high or prolonged fever, an abnormal appearance, an identified focus, a vulnerable host, or incomplete immunisation. [1] [9]

My safety-net would be specific, not "return if worried": the warning changes to watch for (reduced feeding, lethargy, reduced wet nappies, altered breathing, a rash, or the child not being their usual self), the urgency (immediately if any appear), and the exact access route. I would name a clinician who owns any pending test result, confirm understanding with teach-back, and connect the family to primary care follow-up. A brief improvement after antipyretics does not by itself make the child safe; what matters is sustained return to usual behaviour. [1] [3]

Marking grid — SAQ 1

Common pitfalls — SAQ 1

• Applying the 1990s expectant-observation practice (routine culture plus empirical ceftriaxone) to a well-appearing vaccinated toddler.
• Using "return if worried" as the entire safety-net.
• Failing to name an owner for a pending urine or other test.
• Missing a urinary tract infection because no urine was tested in a febrile infant.
• Anchoring on a reassuring antipyretic response without assessing sustained recovery. [1] [3] [9]

SAQ 2 (10 marks, 15 minutes)

Stem. A 28-day-old infant presents with a fever of 38.6 °C. She appears well on first assessment. A nasopharyngeal panel is positive for respiratory syncytial virus. Outline your approach, including which validated pathway you would use, the role of inflammatory markers, the interpretation of the positive viral test, and your disposition. [11]

Model answer — SAQ 2

A febrile infant at 28 days is a high-risk age group and must not be reassured by a well appearance. I would manage her on an age-stratified pathway. The American Academy of Pediatrics guideline and the PECARN prediction rule structure this decision: infants 8 to 21 days with fever are managed as high-risk; infants 22 to 28 days are risk-stratified with inflammatory markers and urinalysis, with lumbar puncture often performed and empirical therapy usual; infants 29 to 60 days can be risk-stratified with the PECARN low-risk rule. This 28-day-old therefore sits in the actively managed band. [2] [3]

I would assess appearance explicitly, measure age-adjusted observations and examine for a focus, then obtain a blood culture (adequate volume), a catheter or suprapubic urine, and bloods including full blood count, C-reactive protein and, where available, procalcitonin. Procalcitonin is the most accurate individual inflammatory marker for invasive and serious bacterial infection in young febrile infants, ahead of C-reactive protein and white-cell count, but no single marker is sensitive or specific enough to rule disease in or out alone. [2] [11]

I would interpret the positive respiratory syncytial virus test carefully. A large PECARN cohort showed that febrile infants 60 days and younger with documented viral infections still carry a measurable risk of serious and invasive bacterial coinfection — lower with RSV than with influenza, but not zero. The positive viral result therefore lowers but does not abolish the need to consider invasive bacterial infection; appearance, age and inflammatory markers still drive the decision. [4]

For disposition, I would admit and treat this infant with empirical intravenous antibiotics per the local neonatal and infant fever pathway, rather than discharge on the basis of the positive viral test or the well appearance, because the residual coinfection risk in this age band is material. I would reassess the trend, narrow therapy according to results, and ensure a named clinician owns the pending cultures. [2] [3]

Marking grid — SAQ 2

Common pitfalls — SAQ 2

• Discharging a 28-day-old febrile infant because of a well appearance or a positive viral test.
• Treating a single inflammatory marker as definitive.
• Drawing an under-filled blood culture.
• Applying an older-child low-prevalence logic to a young infant.
• Failing to name an owner for pending cultures before disposition. [2] [3] [4] [11]