Approach to fever by age and immune status — formative SAQs

SAQ 1 (10)

A 22-day-old term infant presents to ED with a rectal temperature of 38.3 °C. The mother reports poor feeding for 8 hours and says the baby "is not right." The infant is mildly irritable but perfuses well. [1] [6]

1. State your immediate priority and the work-up this infant must receive. (3) [1]
2. Explain why height of fever cannot be used to rule in or rule out serious bacterial infection in this age group. (3) [4]
3. Outline your disposition, empiric management principles (no invented drug doses), and the safety-net you give the family. (4) [1] [6]

Model answer

Immediate priority and work-up. Any fever in a neonate 0–28 days is sepsis until proven otherwise. Immediate priority is ABCDE threat assessment and a full septic work-up — blood culture, complete blood count and differential, urine culture from catheterisation or suprapubic aspirate (not bag), and cerebrospinal fluid from lumbar puncture — with empiric antibiotics and admission regardless of how well the infant appears. [1]

Why fever height is unreliable. De and colleagues showed body temperature lacks accuracy for detecting serious bacterial infection in febrile episodes. Neonates have immature thermoregulation and a weak inflammatory response, so they may be hypothermic or only mildly febrile in sepsis. The magnitude of the cytokine response reflects host thermoregulatory capacity, not organism virulence. Behaviour, perfusion, and feeding matter more than the temperature number. [4]

Disposition, management, safety-net. Admit for observation and empiric antibiotics. Involve senior paediatric and microbiology input. Give the family a written safety-net: return immediately if feeding worsens, breathing difficulty, reduced interaction, abnormal colour, seizures, or parental concern the baby is worse. Caregiver concern is associated with critical illness, so take the mother's "not right" seriously. [1] [6]

SAQ 2 (10)

A 7-year-old on maintenance chemotherapy for acute lymphoblastic leukaemia presents with fever of 38.8 °C at home. On arrival the child looks well and is interactive. The last neutrophil count two days ago was 0.4 × 10⁹/L. [5]

1. State why this child is an emergency despite appearing well, and the immediate management steps (no invented doses). (4) [5]
2. Contrast this child's management with that of a well-appearing, immunocompetent 45-day-old febrile infant. (3) [2] [3] [5]
3. Outline the follow-up and the principles you would communicate to the family. (3) [5]

Model answer

Why an emergency and immediate steps. A febrile neutropenic child can deteriorate within hours from gram-negative bacteraemia, especially Pseudomonas aeruginosa, while looking well, because neutropenia blunts the inflammatory response. Immediate steps: blood cultures from every lumen of any central line and a peripheral site, confirm neutropenia on a current count, and deliver empiric broad-spectrum antibiotics within 60 minutes, then admit. This child does not go home on oral antibiotics. The 2023 fever-and-neutropenia guideline sets this standard. [5]

Contrast with the 45-day-old infant. The well-appearing immunocompetent 45-day-old is risk-stratified with a validated rule — Step-by-Step or the PECARN clinical prediction rule — using appearance, urinalysis, white cell count, neutrophil count, and procalcitonin. A low-risk infant may avoid lumbar puncture and discharge with close follow-up. The neutropenic child, by contrast, gets cultures and empiric antibiotics regardless of appearance because appearance is not a reliable gate in immunocompromise. [2] [3] [5]

Follow-up and family communication. Admit for inpatient observation and ongoing empiric therapy guided by culture results and local protocols. Explain to the family that fever during neutropenia is a medical emergency even when the child looks well, that they must present immediately for any future fever, and that the central line (if present) is checked as a potential source. Agree a clear return-on-fever plan with the oncology team. [5]