Inferring the origin of populations introduced from a genetically structured native range by approximate Bayesian computation: case study of the invasive ladybird Harmonia axyridis.

Correct identification of the source population of an invasive species is a prerequisite for testing hypotheses concerning the factors responsible for biological invasions. The native area of invasive species may be large, poorly known and/or genetically structured. Because the actual source population may not have been sampled, studies based on molecular markers may generate incorrect conclusions about the origin of introduced populations. In this study, we characterized the genetic structure of the invasive ladybird Harmonia axyridis in its native area using various population genetic statistics and methods. We found that native area of H. axyridis most probably consisted of two geographically distinct genetic clusters located in eastern and western Asia. We then performed approximate Bayesian computation (ABC) analyses on controlled simulated microsatellite data sets to evaluate (i) the risk of selecting incorrect introduction scenarios, including admixture between sources, when the populations of the native area are genetically structured and sampling is incomplete and (ii) the ability of ABC analysis to minimize such risks by explicitly including unsampled populations in the scenarios compared. Finally, we performed additional ABC analyses on real microsatellite data sets to retrace the origin of biocontrol and invasive populations of H. axyridis, taking into account the possibility that the structured native area may have been incompletely sampled. We found that the invasive population in eastern North America, which has served as the bridgehead for worldwide invasion by H. axyridis, was probably formed by an admixture between the eastern and western native clusters. This admixture may have facilitated adaptation of the bridgehead population.

Incidence, presenting features, risk factors and significance of late onset septicemia in very low birth weight infants. The National Institute of Child Health and Human Development Neonatal Research Network.

BACKGROUND: Septicemia is a major antecedent of morbidity and mortality in very low birth weight (501- to 1500-g) infants. Our purpose was to determine prospectively the incidence, clinical presentation, laboratory features, risk factors, morbidity and mortality associated with late onset septicemia in infants 501 to 1500 g. METHODS: Clinical data were prospectively collected for 2416 infants enrolled in a multicenter trial to determine the efficacy of intravenous immunoglobulin in preventing nosocomial infections. Septicemia was confirmed by positive blood culture in 395 symptomatic infants. Multivariate analyses of factors associated with septicemia were performed. RESULTS: Sixteen percent of VLBW infants developed septicemia at a median age of 17 days. Factors associated with septicemia by logistic regression included male gender, lower gestational age and birth weight and decreased baseline serum IgG concentrations. Increasing apnea (55%), feeding intolerance, abdominal distension or guaiac-positive stools (43%), increased respiratory support (29%), lethargy and hypotonia (23%) were the dominant presenting features of septicemia. An abnormal white blood cell count (46%), unexplained metabolic acidosis (11%) and hyperglycemia (10%) were the most common laboratory indicators. Septicemic infants, compared with nonsepticemic infants, had significantly increased mortality (21% vs. 9%), longer hospital stay (98 vs. 58 days) and more serious morbidity, including severe intraventricular hemorrhage, bronchopulmonary dysplasia and increased ventilator days (P < 0.001). CONCLUSIONS: Late onset septicemia is common in very low birth weight infants, and the rate is inversely proportional to gestational age and birth weight. Septicemia is more common in males and those with low initial serum IgG values. A set of clinical signs (apnea, bradycardia, etc.) and laboratory values (leukocytosis, immature white blood cells and neutropenia) increase the probability of late onset sepsis, but they have poor positive predictive value.

A controlled trial of intravenous immune globulin to reduce nosocomial infections in very-low-birth-weight infants. National Institute of Child Health and Human Development Neonatal Research Network.

BACKGROUND: Nosocomial infections are a major cause of morbidity and mortality in premature infants. As a rule, their low serum gamma globulin levels at birth subsequently decline to hypogammaglobulinemic values; hence, prophylactic administration of intravenous immune globulin may reduce the rate of hospital-acquired infections. METHODS: In this prospective, multicenter, two-phase controlled trial, 2416 infants were stratified according to birth weight (501 to 1000 g and 1001 to 1500 g) and randomly assigned to an intravenous immune globulin group (n = 1204) or a control group (n = 1212). Control infants were given placebo infusions during phase 1 of the study (n = 623) but were not given any infusions during phase 2 (n = 589). Infants weighing 501 to 1000 g at birth were given 900 mg of immune globulin per kilogram of body weight, and infants weighing 1001 to 1500 g at birth were given a dose of 700 mg per kilogram. The immune globulin infusions were repeated every 14 days until the infants weighed 1800 g, were transferred to another center, died, or were sent home from the hospital. RESULTS: Nosocomial infections of the blood, meninges, or urinary tract occurred in 439 of the 2416 infants (18.2 percent): 208 (17.3 percent) in the immune globulin group and 231 (19.1 percent) in the control group (relative risk, 0.91; 95 percent confidence interval, 0.77 to 1.08). Septicemia occurred in 15.5 percent of the immune globulin recipients and 17.2 percent of the controls. During phase 1 the rate of nosocomial infections was 13.4 percent in the immune globulin group and 17.8 percent in the control group; the respective rates during phase 2 were 21.0 percent and 20.4 percent. The predominant organisms included gram-positive cocci (53.0 percent), gram-negative bacilli (22.4 percent), and candida species (16.0 percent). Adverse reactions were rarely observed during the infusions. Immune globulin therapy had no effect on respiratory distress syndrome, bronchopulmonary dysplasia, intracranial hemorrhage, the duration of hospitalization, or mortality. The incidence of necrotizing enterocolitis was 12.0 percent in the immune globulin group and 9.5 percent in the control group. CONCLUSIONS: Prophylactic use of intravenous immune globulin failed to reduce the incidence of hospital-acquired infections in very-low-birth-weight infants.

Dexamethasone effects on the hospital course of infants with bronchopulmonary dysplasia who are dependent on artificial ventilation.

A randomized double-blind placebo-controlled trial was conducted to evaluate the effects of enterally administered dexamethasone on the hospital course of infants with bronchopulmonary dysplasia. A total of 23 infants with a birth weight less than 1500 g who were dependent on artificial ventilation 3 to 4 weeks of age received dexamethasone (n = 12) or saline placebo (n = 11). Dexamethasone (0.5 mg/kg per day) was given in tapering doses for 7 days followed by hydrocortisone (8 mg/kg per day) which was progressively reduced for a total of 17 days of therapy. Infants who received dexamethasone required less oxygen on days 8 and 17 (P less than .05) and were more likely to extubate 8 days after therapy than infants in the control group (respectively 8/12 vs 3/11 infants, P less than .05; P = .12 after Yates correction). The use of dexamethasone significantly shortened median duration of mechanical ventilation (4 vs 22 days, P less than .05) but had no effect on length of oxygen therapy, hospitalization, home oxygen therapy, occurrence and severity of retinopathy of prematurity, rate of growth, and mortality. No significant complications resulted from dexamethasone therapy. Measurements of plasma dexamethasone levels confirmed the absorption of drug from the gastrointestinal tract (23.7 ng/mL in dexamethasone vs 4.6 ng/mL in the control group, P less than .05). Dexamethasone administration resulted in short-term improvements in pulmonary function but did not ameliorate the hospital course of infants with bronchopulmonary dysplasia.

Maternal administration of vitamin K does not improve the coagulation profile of preterm infants.

The effect of maternal administration of vitamin K1 on cord blood prothrombin time, activated partial thromboplastin time, activity of factors II, VII, and X, and antigen levels of factors II and X in infants less than 35 weeks' gestation was evaluated. Pregnant women in preterm labor were randomly assigned to receive 10 mg of vitamin K1 intramuscularly or no injection. If delivery did not occur in 4 days, the dose of vitamin K1 was repeated. Women who continued their pregnancy 4 days beyond the second dose received 20 mg of vitamin K1 orally daily until the end of the 34th week of gestation. The birth weights of infants ranged from 370 to 2550 g and gestational age ranged from 22 to 34 weeks. The prothrombin time, activated partial thromboplastin time, factors II, VII, and X activity, and factors II and X antigen levels were not statistically different in either group of infants. Intraventricular hemorrhage occurred in 25 of 51 control infants and 25 of 47 vitamin K-treated infants. More control infants had grade III intraventricular hemorrhage on day 1 (P = .032), but on day 3 and 14 of life, the severity of intraventricular hemorrhage was comparable in both groups. Infants in whom an intraventricular hemorrhage developed were significantly smaller, younger, and more critically ill than infants without intraventricular hemorrhage. Administration of vitamin K1 to pregnant women at less than 35 weeks' gestation does not improve the hemostatic defects nor does it reduce the incidence or severity of intraventricular hemorrhage in their infants.

Endotracheal tubes in neonates: sonographic positioning.

Twenty-one real-time sonographic determinations of endotracheal tube tip position were performed in 16 neonates. Findings were compared with those from simultaneously obtained chest radiographs. Relation of the tube tip to the aortic arch provided a reliable method of determination of appropriate position. Optimal tube tip position was seen when the tube tip was 1 cm above the arch.

Implementation of a statewide perinatal automated medical network (PAM/NET) for Michigan.

PAM/NET is a computerized data base and conferencing system used by nine neonatal intensive care units in Michigan and Illinois. The system depends on the timesharing resource of a large university mainframe computer. The data base functions are managed by a sophisticated inverted file relational data base management system capable of mass storage and rapid and specific retrieval of individual cases or summary data. Data stored in the system are used to generate admission, discharge and developmental assessment clinic summaries that serve as such for the medical record and as letters to primary physicians. We report here the early experience in the design and dissemination of this database network to the participating hospitals. Conflicting goals of sharing and confidentiality of clinical data are addressed in the design of this system.

Antenatal phenobarbital for the prevention of neonatal intracerebral hemorrhage.

Forty-six pregnant women less than 35 weeks of gestation were enrolled in a prospective randomized controlled study evaluating the effects of antenatal phenobarbital on neonatal intracerebral hemorrhage. The women were randomly assigned to control (n = 22) or treatment (n = 24) groups; the treatment group received 500 mg of phenobarbital intravenously. The time interval between the dose of phenobarbital and delivery was 5.5 +/- 4.8 hours (mean +/- SD). The infants in the control group (n = 23) and those in the phenobarbital-treated group (n = 25) were comparable regarding birth weight, gestational age, and other obstetric and neonatal risk factors associated with intracerebral hemorrhage. The incidence of intracerebral hemorrhage was 56.5% (13 of 23 infants) in the control group and 32% (eight of 25 infants) in the phenobarbital-treated group (p = 0.08). Moderate or severe hemorrhage was diagnosed in six of 13 control infants and in none of the phenobarbital-treated infants (p less than 0.01). The mortality rate was significantly lower in the phenobarbital-treated group (two of 25 infants) than in the control group (eight of 23 infants; p less than 0.05). Our study suggests that antenatal phenobarbital administration results in a decrease in mortality and in the severity of intracerebral hemorrhage in the preterm neonate.

Analysis of the effects of applying federal diagnosis-related grouping (DRG) guidelines to a population of high-risk newborn infants.

Length of stay data collected for high-risk newborn infants admitted to a tertiary care children's hospital neonatal unit over a 6-year period were compared with mean and outlier lengths of stay published in the Federal Register as part of a proposed system for prospective payment of hospital cost by diagnosis-related groupings (DRGs). We found that the classification system for newborns markedly underestimated the number of days required for the treatment of these infants. The use of the geometric mean instead of the arithmetic mean as the measure of central tendency was a significant contributor to the discrepancy, especially in those subgroups with bimodal frequency distributions of lengths of stay. Another contributor to the discrepancy was the lack of inborn patients in the children's hospital cohort. The system of prospective payments, as outlined, does not take into account several factors that have a strong influence on length of stay such as birth weight (which requires more than three divisions to serve as an effective predictor), surgery, outborn status, and ventilation. Implementation of the system described in the Federal Register would severely discourage tertiary care referral hospitals from providing neonatal intensive care.