Where have all the neutrophils gone?

An 8-week-old boy presented with a history of fever associated with an ulcerating rash over both hips that had worsened over the preceding 5 days (fig 1). He was the first child of non-consanguineous West African parents, the pregnancy having been uneventful. His mother was known to be HbSC trait and had no history of previous miscarriages or infant deaths. The child was delivered in good condition by emergency lower segment caesarean section for failure to progress with a birth weight of 3.69 kg. At presentation he was thriving along the 50th centile. He had received the BCG vaccine in the neonatal period but had not received any further vaccines. He had also had a pustular groin rash that had developed at 4 weeks of age and had spontaneously resolved.

The patient was empirically started on iv flucloxacillin and gentamicin. His full blood count revealed significant anaemia with an Hb of 6.6 g/dl (MCV 73 fl), a marked neutropenia (WCC 7.6×10⁹/l, neutrophils 0×10⁹/l, lymphocytes 3.2×10⁹/l, eosinophils 0×10⁹/l, monocytes 4.4×10⁹/l, basophils 0×10⁹/l) and normal platelets. His C-reactive protein was significantly raised at 275 mg/l (normal range 0–10 mg/l). In view of the absolute neutropenia and severe anaemia, an underlying haematological pathology was considered and the patient was referred to a tertiary paediatric haematology centre.

COMMENT 1: Causes of neutropenia in infants

• Box 1 outlines the wide differential list for neutropenia in infancy.1

• Some 25% of healthy black babies may have a neutrophil count of <1.0×10⁹/l.2

A skin swab from the patient’s hip grew a fully sensitive strain of Staphylococcus aureus. In view of this, the possibility of a toxin-mediated process was considered and clindamycin was added to his antibiotic regimen. Over the …