• haemopoiesis
• neutrophils
• colony stimulating factors
• sepsis

Bacterial and fungal sepsis is a major cause of morbidity and mortality in neonates. Infection rates are high in infants treated in intensive care units, with the highest rates, of around 30%, occurring in extremely immature preterm neonates.1-3 A survey of neonatal infection at Yale University, ongoing since 1928,4 has documented a decline in neonatal septic deaths commensurate with the establishment of neonatal intensive care units and the liberal use of increasingly effective antibiotics. Mortality from sepsis declined steadily until the early 1980s, but since then it has remained constant at near 15%. This plateau of mortality most likely reflects the poor host defences of immature, preterm neonates.5

Neutrophil leucocytes are central to the defences against bacterial infection,6 and in neonates both neutrophil production and function are immature. Neutropenia, defined as a neutrophil count below the normal range for neonates established by Monroe,7occurs in up to 35% of preterm neonates8 9 and in 50% of all infants born to mothers with pregnancy induced hypertension.10 The development of sepsis together with neutropenia carries a high mortality of 39%, and two out of every three septic infants whose neutrophils fall below 0.5 × 10⁹/l will die.9