Complement activation in neonatal infection

Evaluation of microbiologic and hematologic parameters and E-selectin as early predictors for outcome of neonatal sepsis

CONTEXT

Early diagnosis of neonatal sepsis is mandatory. Various markers are used to diagnose the condition.

OBJECTIVE

To evaluate the diagnostic value of various clinical data and hematologic parameters, such as total leukocyte count, absolute neutrophil count, immature to total neutrophil ratio, and soluble E-selectin (sE-selectin) in identification and outcome of neonatal sepsis.

DESIGN

Newborn infants with a clinical diagnosis of sepsis in the neonatal intensive care unit at Mansoura University Children's Hospital during the period between July 2007 and December 2007 were eligible for study. In addition, 30 healthy neonates were included in the study. Complete hematologic and microbiologic laboratory investigations were performed, and serum E-selectin was measured.

RESULTS

Plasma sE-selectin levels were significantly higher (P < .001) in infected infants (mean [SD], 156.9 [77.0] ng/mL) than in noninfected (mean [SD], 88.8 [47.1] ng/mL) and healthy infants (mean [SD], 8.67 [3.74] ng/mL). Infants with gram-negative sepsis had higher sE-selectin levels than did those with gram-positive sepsis (P = .04). C-reactive protein was the best laboratory test for diagnosis of neonatal sepsis, with an overall sensitivity and specificity of 86% and 97%, respectively. Performing sE-selectin with C-reactive protein or immature to total ratio tests increased the specificity, but reduced the sensitivity, of the tests for the determination of neonatal sepsis. Plasma sE-selectin levels were higher in nonsurvivors than in survivors (P = .01) and were higher in those with hemodynamic dysfunction than in those without hemodynamic dysfunction (P < .001).

CONCLUSIONS

We conclude that plasma sE-selectin levels are elevated in neonatal sepsis. Significant elevation was associated with gram-negative sepsis. Plasma sE-selectin had low diagnostic value when used alone or in combination with other tests; however, it can be used as a prognostic indicator for the outcome of neonatal sepsis.

Identifying febrile young infants with bacteremia: is the peripheral white blood cell count an accurate screen?

STUDY OBJECTIVE

We estimated the accuracy of the total peripheral WBC count as a screen for bacteremia in febrile young infants.

METHODS

We evaluated, retrospectively, the performance characteristics of linear and nonlinear (U-shaped) logistic models for predicting bacteremia that are based on the total peripheral WBC count. Research subjects were consecutive 0- to 89-day-old infants who had a temperature in triage of greater than or equal to 38 degrees C (> or =100.4 degrees F) and were evaluated for infection at a pediatric emergency department (1993 to 1999). Infants with leukemia were excluded. Areas under the receiver operator characteristic curves (AUC), as well as sensitivity, specificity, interval likelihood ratios, and the corresponding odds of bacteremia predicted at various thresholds of the test, were calculated.

RESULTS

The rate of bacteremia was 1% (38/3,810). The U-shaped model was more accurate (AUC 0.69 versus 0.56); however, no threshold of the total peripheral WBC count had both good sensitivity and specificity. Sensitivity and specificity values were 79% and 5%, respectively, at a peripheral WBC count cutoff of 5,000 cells/mm(3), and 45% and 78%, respectively, at a cutoff of 15,000 cells/mm(3). The odds of bacteremia were not decreased substantially at any cutoff and were increased only modestly at values outside published norms of the test.

CONCLUSION

The total peripheral WBC count is an inaccurate screen for bacteremia in febrile young infants; thus, decisions to obtain blood cultures should not rely on this test.

The analysis of the complement activation product SC5 b-9 is applicable in neonates in spite of their profound C9 deficiency

Native complement factors and complement activation products were measured in healthy neonates (n = 72) and in a group of infants with premature prolonged rupture of the membranes (PPROM) without sepsis (n = 10). Vitronectin concentration in normal cord blood was not correlated with gestational age, and the median value was 86.0% of adult values. This was markedly higher than other native complement factors studied (factor B: 35.9%, C4: 45.1%, C3: 56.2%). The concentration of C9 showed a positive correlation with gestational age and was very low, 10.8% of normal adult values in cord blood and 8.3% in the patients. Fifteen percent of the neonates had C9 levels lower than 2% of adult values. The complement activation products Bb and SC5 b-9 were significantly elevated in the patients (159% and 130% of control values, respectively), indicating alternative and terminal pathway activation. In contrast, C4 bc and C3 bc levels were not increased. The maximum amount of SC5 b-9 which could be generated in the neonatal sera by cobra venom factor was highly correlated with C9 concentration (rs = 0.86, p = 0.0001) The profound C9 deficiency found in neonates is correlated with gestational age, limits the capacity to form bacteriolytic C5 b-9 (m) and may predispose for severe invasive bacterial infection. The plasma level of SC5 b-9 under normal conditions was very low, only 0.3% (0.1%-3.0%) of the values obtained after CVF activation of the same samples. Therefore, we suggest that the analysis of SC5 b-9 is applicable also in neonates, in spite of their extremely low C9 levels.

Reduction of unnecessary antibiotic therapy in newborn infants using interleukin-8 and C-reactive protein as markers of bacterial infections

OBJECTIVE

To examine whether the determination of interleukin 8 (IL-8) and C-reactive protein (CRP) in neonates with suspected nosocomial bacterial infection (NBI) is feasible and cost-effective in reducing antibiotic therapy.

METHODS

Between April 1996 and May 1997, IL-8 was measured 260 times along with blood cultures, CRP, and immature-to-total-neutrophil (IT) ratio for suspected NBI in term and preterm neonates. All infants were retrospectively analyzed for NBI. Sensitivity, specificity, positive and negative predictive values, and 95% confidence intervals were calculated for IL-8, CRP, and IT ratio. Receiver-operating characteristic curves were analyzed to determine optimal thresholds. Between June 1997 and June 1998, IL-8 was measured 215 times in newborn infants with suspected NBI and the decision to start antibiotic therapy was based on increased IL-8 and/or CRP values. A cost-effectiveness analysis was performed and sensitivity, specificity, and receiver-operating characteristic curves were reevaluated.

RESULTS

At the first suspicion of NBI, the combination of IL-8 >/= 53 pg/mL and/or CRP >10 mg/L detected culture-proven NBI with 96% sensitivity. The combined culture-proven and clinical NBI were detected with 93% sensitivity and 80% specificity. The use of IL-8 reduced unnecessary antibiotic therapy for suspected NBI by 73% and was cost-effective when compared with initiating antibiotic therapy based on clinical signs alone or based on clinical signs and an increased IT ratio and/or CRP.

CONCLUSIONS

The combination of IL-8 and/or CRP is a reliable and early test for the diagnosis of NBI in newborn infants. Using the combination of IL-8 and/or CRP to restrict antibiotic therapy to truly infected infants reduces unnecessary antibiotic therapy and is cost-effective.

Diagnostic tests for bacterial infection from birth to 90 days--a systematic review

AIM

To determine the clinical value of common diagnostic tests for bacterial infection in early life.

METHODS

A Medline search (1966-95) was undertaken to identify studies that reported the assessment of a diagnostic "test," predicting the presence or absence of bacterial infection in infants up to 90 days of age. The quality of each selected study was assessed using defined criteria. Data were extracted twice to minimise errors.

RESULTS

Six hundred and seventy articles were identified. Two independent investigators agreed that 194 studies met the inclusion criteria (kappa = 0.85), 52 of which met primary quality criteria; 23 studies reported data on (a) haematological indices, (b) C reactive protein evaluation, and (c) surface swab assessment. For haematological indices, the likelihood ratios for individual tests ranged from 20.4 (95% confidence interval 7.3 to 56.8) for a white cell count < 7000/mm3 to 0.12 (0.04 to 0.37) for an immature:total (I:T) white cell ratio < 0.2. For C reactive protein evaluation, the likelihood ratios ranged from 12.56 (0.79 to 199.10) for a value of > 6 mg/l to 0.22 (0.08 to 0.65) for a negative value. For surface swab assessment, the likelihood ratios ranged from 33.6 (2.1 to 519.8) for a positive gastric aspirate culture to 0.08 (0.006 to 1.12) for microscopy of ear swab material that did not show any neutrophils. Likelihood ratios for combinations of these individual tests ranged from 10.17 (3.64 to 28.41) to 0.47 (0.22 to 1.00).

CONCLUSIONS

The methodological quality of studies assessing the accuracy of diagnostic tests is generally poor. Even in rigorous studies, the reported accuracy of the tests varies enormously and they are of limited value in the diagnosis of infection in this population.

The value of immunoglobulin and complement levels in the early diagnosis of neonatal sepsis

Serum IgG, IgG1, G2, G3, G4, IgM, C3c and C4 concentrations were measured in 24 term neonates with sepsis and 17 healthy normal neonates of similar age, sex and weight (control group). The serum IgG, IgG1, G2, G3, G4, IgM, C3c, and C4 levels were similar in the patients with sepsis and the control group (p > 0.05). In the neonates with sepsis, serum IgG, G1, G2, IgM and C4 levels were not significantly different between the 1st and 10th days, while there were significant differences for IgG3, G4 and C3c (p < 0.05). We conclude that the serum levels of IgG, IgG1, G2, G3, G4, IgM, C3c and C4 concentrations are of no value for the early diagnosis of neonatal sepsis.

Alternative pathway activation of the complement system in preterm infants with early onset infection

The increased incidence of infection in preterm neonates has been related in part to their relative deficiency of most complement components, because complement is known to participate in the defense against bacterial and viral infections. In a prospective study, complement activation products were determined in 52 preterm infants. Twenty preterm infants suffered from proven early onset infection, 11 infants were presumed to suffer from infection, which could not be confirmed. Twenty-one preterm infants without infection or perinatal asphyxia formed the control group. EDTA plasma was obtained within the first 6 h after birth, and follow-up examinations were done in 15 patients with proven infection during the next 24 h. The complement activation products C3a-desArg, C3bBbP, and sC5b-9 were measured with enzyme immunoassay systems. In preterm neonates with early onset infection, a significant elevation of C3a-desArg was found in the very early course of the disease. C3a-desArg generation resulted from alternative pathway activation as shown by a concurrent increase of C3bBbP concentration. In addition, significantly higher concentrations of sC5b-9 predicted infection in the first few hours after birth. Thus, despite very low levels of native complement proteins, preterm babies are able to generate remarkable amounts of activation products of the complement cascade. The elevation of these activation products preceded by hours significant changes of routine laboratory markers of infection, such as leukocyte count, differential blood count, and C-reactive protein. Thus they might help to identify preterm neonates with severe systemic infection earlier than other laboratory parameters.

Effect of fresh frozen plasma and gammaglobulin on humoral immunity in neonatal sepsis

Fresh frozen plasma and intravenous immunoglobulin are used as prophylaxis against, and for the treatment of, neonatal infection. It is assumed that any beneficial effect is mediated through the humoral immune factors contained in each preparation. The effect of fresh frozen plasma and intravenous immunoglobulin on humoral immune markers (immunoglobulins and IgG subclasses, complement components and activation products, and C reactive protein) was investigated over a 24 hour period after their randomised administration to 67 infants with suspected infection. Thirty infants without suspicion of infection were studied as controls. Compared with control infants, infants with suspected infection had increased concentrations of C reactive protein, reduced concentrations of fibronectin, and increased concentrations of the complement activation marker C3d, but similar concentrations of IgG, IgG subclasses, IgA, and IgM. After intravenous immunoglobulin treatment (500 mg/kg) concentrations of total IgG and all IgG subclasses increased, as did IgA and complement component C4. Concentrations of C reactive protein decreased after intravenous immunoglobulin treatment and were significantly lower than baseline after 24 hours. In contrast, no change in IgG or IgG subclass concentrations occurred after fresh frozen plasma administration. At 24 hours after fresh frozen plasma administration, concentrations of IgA, IgM, and C4 were significantly higher than baseline and serum IgA was significantly higher than in infants tested 24 hours after intravenous immunoglobulin treatment. These results confirm the rational basis for intravenous immunoglobulin treatment but question the value of fresh frozen plasma, particularly in the light of its attendant problems as an untreated blood product.