Neonatal sepsis: a difficult diagnostic challenge

Neonatal systemic infection is a leading cause of morbidity andmortality both in industrialized and developing countries.The increasing survival rates of preterm neonates with progres-sively lower gestational age and birth weight have been associatedwith higher occurrence of sepsis. Stratified by weight, approximately10% of 1000–1500 g infants and 35% of less than 1000 g babies willreceive a diagnosisof sepsis during their neonatalperiod. Early- onsetsepsis is acquired during the first 72 h of life via generally a verticalroute. Late-onset sepsis is much more common and infection comesgenerally from invasive devices and direct contact with parents andhealthcarepersonnel.Sepsisisresponsibleforroughly50%ofneonataldeaths after 2 weeks of life. Coagulase-negative staphylococci are theprevalent infecting organisms followed by E. coli and multidrugresistantGram-negativeorganismsincludingKlebsiella,Pseudomonasand fungi.Clinical presentation may start from subtle and unspecific signs(temperature instability, feeding intolerance, prolonged jaundice)and lead rapidly to catastrophic events such as death or permanentneurological impairment. Timely diagnosis is a greatly neededresearch goal. Current laboratory tests (CRP, total whites count,absolute neutrophil count, immature to total neutrophil ratio),individually or in combination, do not reach sufficient specificityand sensitivity. The diagnostic gold standard relies on the microor-ganism isolation, though generally only one out of five sepsisevaluation will result in a positive blood culture.Novel diagnostic tools for neonatal sepsisIn recent years a different approach has been attempted indiagnosing sepsis.The VCS technology of the Coulter LH 750 hematology analyzer(Beckman Coulter, Fullerton, CA) can obtain directly data from morethan 8000 WBCs using direct current impedance to measure cellvolume (V) for accurate size of all cell types, radio frequency opacityto characterize conductivity (C) for internal composition of each cell,and a laser beam to measure light scatter (S) for cytoplasmicgranularity andnuclearstructure.These datathen areused to identifyeach cell as a neutrophil, lymphocyte, monocyte, eosinophil, orbasophil, generating an automated differential count.However, the use of the VCS technology to evaluate morphologicchanges within the same cell population, such as the previouslydescribed neutrophil changes during acute bacterial infection, hasnever been well studied.Band forms and other immature granulocytes (metamyelocytes,myelocytes), as well as reactive segmented neutrophils, tend to belarger and have lower nuclear complexity than their normal“resting” counterparts. Therefore, Chaves et al. proposed that themorphologic changes seen in the left-shifted and reactivesegmented neutrophils could be analyzed quantitatively by usingthe Coulter LH 750 with VCS technology. These investigatorsevaluated the clinical usefulness of these morphologic parameters(also referred to as positional parameters) as possible indicators ofan acute infectious process. In a retrospective series of 69 adultseptic patients and 35 controls, the mean channel for meanneutrophil volume (MNeV) was significantly increased. With an150 MNeV cut-off, a specificity of 91% and a sensitivity of 70% wasachieved. A different series from the same research groupevaluated the usefulness of neutrophil volume distribution width(NDW). This parameter, too, was shown to correlate with apositive blood culture and an NDW cut-off of 23 produced aspecificity of 100% and a sensitivity of 69%.Our group conducted the first investigation using the VCStechnology in diagnosing late-onset neonatal sepsis. In a prospectiveseries of 120 very low birth weight newborns, a MNeV cut-off of 148produced a specificity of and sensitivity of in detecting late-onsetneonatal sepsis on a single determination. MNeV performed betterthananyother individualitem onthe rule outsepsispanel. NDWonlygave a specificity of 88% and a sensitivity of 95%.A larger, multicenter study is currently underway to validate theuse of positional parameters in screening for neonatal sepsis. Also,positional parameters have a potential role in detecting early-onsetsepsis and in guiding the length of antibiotic therapy. Due to theseverity of the disease, clinicians eagerly await an answer from thispromising field of investigation.