Antibiotic Use in Term and Near-Term Newborns

External Evaluation of Population Pharmacokinetic Models of Piperacillin in Preterm and Term Patients from Neonatal Intensive Care

BACKGROUND AND OBJECTIVES

Piperacillin/tazobactam is extensively used off-label to treat late-onset neonatal sepsis, but safety and pharmacokinetic data in this population are limited. Additionally, the organic immaturity of the newborns contributes to a high piperacillin pharmacokinetic variability. This affects the clinical efficacy of the antibiotic treatment and increases the probability of developing drug resistance. This study aimed to evaluate the predictive performance of reported piperacillin population pharmacokinetic models for their application in a model-informed precision dosing strategy in preterm and term Mexican neonatal intensive care patients.

METHODS

Published population pharmacokinetic models for piperacillin which included neonates in their study population were identified. From the reference models, structured models, population pharmacokinetic parameters, and interindividual and residual variability data were extracted to be replicated in pharmacokinetic software (NONMEM® version 7.4). For the clinical study, a sampling schedule was designed, and 2-3 blood samples of 250 µL were taken from neonates who met the inclusion criteria. Piperacillin plasma concentrations were determined by liquid chromatography/tandem mass spectrometry. The clinical treatment data were collected, and piperacillin plasma concentrations were estimated using reference pharmacokinetic models for an a priori or Bayesian approach. Statistical methods were used in terms of bias and precision to evaluate the differences between observed and estimated neonatal piperacillin plasma concentrations with the different approaches and to identify the pharmacokinetic model that best fits the neonatal data.

RESULTS

A total of 70 plasma samples were collected from 25 neonatal patients, of which 15 were preterm neonates. The overall median value (range) postnatal age, gestational age, body weight, and serum creatinine at the sampling collecting day were 12 (3-26) days, 34.2 (26-41.1) weeks, 1.78 (0.08-3.90) Kg, 0.47 (0.20-0.90) mg/dL, respectively. Three population pharmacokinetic models for piperacillin in infants up to 2 months were identified, and their predictive performance in neonatal data was evaluated. No pharmacokinetic model was suitable for our population using an a priori approach. The model published by Cohen-Wolkowiez et al. in 2014 with a Bayesian approach showed the best performance of the pharmacokinetic models evaluated in our neonatal data. The procedure requires two blood samples (predose and postdose), and, when applied, it predicted 66.6% of the observations with a relative median absolute predicted error of less than 30%.

CONCLUSIONS

The population pharmacokinetic model developed by Cohen-Wolkowiez et al. in 2014 demonstrated superior performance in predicting the plasma concentration of piperacillin in preterm and term Mexican neonatal intensive care patients. The Bayesian approach, including two different piperacillin plasma concentrations, was clinically acceptable regarding bias and precision. Its application for model-informed precision dosing can be an option to optimize the piperacillin dosage in our population.

Neonatal bacterial sepsis

Neonatal sepsis remains one of the key challenges of neonatal medicine, and together with preterm birth, causes almost 50% of all deaths globally for children younger than 5 years. Compared with advances achieved for other serious neonatal and early childhood conditions globally, progress in reducing neonatal sepsis has been much slower, especially in low-resource settings that have the highest burden of neonatal sepsis morbidity and mortality. By contrast to sepsis in older patients, there is no universally accepted neonatal sepsis definition. This poses substantial challenges in clinical practice, research, and health-care management, and has direct practical implications, such as diagnostic inconsistency, heterogeneous data collection and surveillance, and inappropriate treatment, health-resource allocation, and education. As the clinical manifestation of neonatal sepsis is frequently non-specific and the current diagnostic standard blood culture has performance limitations, new improved diagnostic techniques are required to guide appropriate and warranted antimicrobial treatment. Although antimicrobial therapy and supportive care continue as principal components of neonatal sepsis therapy, refining basic neonatal care to prevent sepsis through education and quality improvement initiatives remains paramount.

Incidence of Antibiotic Exposure for Suspected and Proven Neonatal Early-Onset Sepsis between 2019 and 2021: A Retrospective, Multicentre Study

Management of suspected early-onset sepsis (EOS) is undergoing continuous evolution aiming to limit antibiotic overtreatment, yet current data on the level of overtreatment are only available for a select number of countries. This study aimed to determine antibiotic initiation and continuation rates for suspected EOS, along with the incidence of culture-proven EOS in The Netherlands. In this retrospective study from 2019 to 2021, data were collected from 15 Dutch hospitals, comprising 13 regional hospitals equipped with Level I-II facilities and 2 academic hospitals equipped with Level IV facilities. Data included birth rates, number of neonates started on antibiotics for suspected EOS, number of neonates that continued treatment beyond 48 h and number of neonates with culture-proven EOS. Additionally, blood culture results were documented. Data were analysed both collectively and separately for regional and academic hospitals. A total of 103,492 live-born neonates were included. In 4755 neonates (4.6%, 95% CI 4.5-4.7), antibiotic therapy was started for suspected EOS, and in 2399 neonates (2.3%, 95% CI 2.2-2.4), antibiotic treatment was continued beyond 48 h. Incidence of culture-proven EOS was 1.1 cases per 1000 live births (0.11%, 95% CI 0.09-0.14). Overall, for each culture-proven EOS case, 40.6 neonates were started on antibiotics and in 21.7 neonates therapy was continued. Large variations in treatment rates were observed across all hospitals, with the number of neonates initiated and continued on antibiotics per culture-proven EOS case varying from 4 to 90 and from 4 to 56, respectively. The high number of antibiotic prescriptions compared to the EOS incidence and wide variety in clinical practice among hospitals in The Netherlands underscore both the need and potential for a novel approach to the management of neonates with suspected EOS.

Antimicrobial Stewardship Programs in Neonates: A Meta-Analysis

BACKGROUND AND OBJECTIVES

Neonatal sepsis is a significant contributor to mortality and morbidity; however, the uncontrolled use of antimicrobials is associated with significant adverse effects. Our objective with this article is to review the components of neonatal antimicrobial stewardship programs (ASP) and their effects on clinical outcomes, cost-effectiveness, and antimicrobial resistance.

METHODS

We selected randomized and nonrandomized trials and observational and quality improvement studies evaluating the impact of ASP with a cutoff date of May 22, 2023. The data sources for these studies included PubMed, Medline, Embase, Cochrane CENTRAL, Web of Science, and SCOPUS. Details of the ASP components and clinical outcomes were extracted into a predefined form.

RESULTS

Of the 4048 studies retrieved, 70 studies (44 cohort and 26 observational studies) of >350 000 neonates met the inclusion criteria. Moderate-certainty evidence reveals a significant reduction in antimicrobial initiation in NICU (pooled risk difference [RD] 19%; 95% confidence interval [CI] 14% to 24%; 21 studies, 27 075 infants) and combined NICU and postnatal ward settings (pooled RD 8%; 95% CI 6% to 10%; 12 studies, 358 317 infants), duration of antimicrobial agents therapy (pooled RD 20%; 95% CI 10% to 30%; 9 studies, 303 604 infants), length of therapy (pooled RD 1.82 days; 95% CI 1.09 to 2.56 days; 10 studies, 157 553 infants), and use of antimicrobial agents >5 days (pooled RD 9%; 95% CI 3% to 15%; 5 studies, 9412 infants). Low-certainty evidence reveals a reduction in economic burden and drug resistance, favorable sustainability metrices, without an increase in sepsis-related mortality or the reinitiation of antimicrobial agents. Studies had heterogeneity with significant variations in ASP interventions, population settings, and outcome definitions.

CONCLUSIONS

Moderate- to low-certainty evidence reveals that neonatal ASP interventions are associated with reduction in the initiation and duration of antimicrobial use, without an increase in adverse events.

Antibiotic Use in Late Preterm and Full-Term Newborns

Importance

Antibiotic treatment saves lives in newborns with early-onset sepsis (EOS), but unwarranted antibiotic use is associated with resistant bacteria and adverse outcomes later in life. Surveillance is needed to optimize treatment strategies.

Objective

To describe antibiotic use in association with the incidence and mortality from EOS among late-preterm and full-term newborns.

Design, Setting, and Participants

The Sweden Neonatal Antibiotic Use study was a nationwide observational study that included all late-preterm and full-term neonates born from January 1, 2012, to December 31, 2020, in neonatal units of all levels. All hospital live births from 34 weeks' gestation during the study period were included in the study. Data were collected from the Swedish Neonatal Quality Register and the Swedish Medical Birth Register. Data were analyzed from August 2022 to May 2023.

Exposure

Admission for neonatal intensive care during the first week of life.

Main Outcomes and Measures

The main outcomes were the usage of intravenous antibiotics during the first week of life, the duration of antibiotic therapy, the rate of culture-proven EOS, and mortality associated with EOS.

Results

A total of 1 025 515 newborns were included in the study; 19 286 neonates (1.88%; 7686 girls [39.9%]; median [IQR] gestational age, 40 [38-41] weeks; median [IQR] birth weight, 3610 [3140-4030] g) received antibiotics during the first week of life, of whom 647 (3.4%) had EOS. The median (IQR) duration of antibiotic treatment in newborns without EOS was 5 (3-7) days, and there were 113 antibiotic-days per 1000 live births. During the study period there was no significant change in the exposure to neonatal antibiotics or antibiotic-days per 1000 live births. The incidence of EOS was 0.63 per 1000 live births, with a significant decrease from 0.74 in 2012 to 0.34 in 2020. Mortality associated with EOS was 1.39% (9 of 647 newborns) and did not change significantly over time. For each newborn with EOS, antibiotic treatment was initiated in 29 newborns and 173 antibiotic-days were dispensed.

Conclusions and Relevance

This large nationwide study found that a relatively low exposure to antibiotics is not associated with an increased risk of EOS or associated mortality. Still, future efforts to reduce unwarranted neonatal antibiotic use are needed.

Switch from intravenous-to-oral antibiotics in neonatal probable and proven early-onset infection: a prospective population-based real-life multicentre cohort study

OBJECTIVE

To evaluate the implementation of switch from intravenous-to-oral antibiotic therapy with amoxicillin in neonates with early-onset infection (EOI).

DESIGN, SETTING AND PATIENTS

A population-based multicentre cohort study. All term-born neonates with EOI were prospectively included between 1 December 2018 to 30 November 2020.

INTERVENTION

Intravenous-to-oral switch antibiotic therapy in clinically stable neonates.

MAIN OUTCOME MEASURES

The primary outcome was readmission due to infection. Secondary outcomes were days of hospitalisation and antibiotic use in the pre-implementation versus post implementation period.

RESULTS

During 2 years, 835 neonates commenced antibiotics for EOI (1.5% (95% CI 1.4% to 1.6%)) of all term live births). Of those, 554 (66%) underwent a full course of treatment. There were 23 episodes of culture-proven infection (0.42 per 1000 term live births (95% CI 0.27 to 0.63)). A total of 478 of 531 (90%) neonates with probable infection underwent switch therapy. None was readmitted due to infection. The median duration of hospitalisation was 3.0 days (IQR 2.5-3.5) and 7.4 days (IQR 7.0-7.5) in the switch and intravenous therapy groups, respectively. According to antibiotic surveillance data, 1.2% underwent a full course of treatment following implementation of oral switch therapy (2019-2020), compared with 1.2% before (2017-2018).

CONCLUSION

In clinical practice, switch therapy was safe and used in 9 of 10 neonates with probable EOI. Knowledge of the safety of antibiotic de-escalation is important as home-based oral therapy ameliorates the treatment burden for neonates, caregivers and healthcare systems. Despite the ease of oral administration, implementation of switch therapy did not increase the overall use of antibiotics.

Herpes simplex virus infection among neonates suspected of invasive bacterial infection: a population-based cohort study

OBJECTIVE

To estimate the incidence of neonatal herpes simplex virus (HSV) infection and the number of neonates with suspected invasive bacterial infection (IBI) needed to treat (NNT) with acyclovir to ensure prompt treatment of invasive HSV infections.

DESIGN

A nationwide population-based cohort study.

SETTING

All neonatal and paediatric emergency departments in Denmark from 1 January 2010 to 31 December 2019.

PATIENTS

Neonates aged 0-28 days with HSV infection.

MAIN OUTCOME MEASURES

The main outcome measures were incidence and NNT. The NNT was calculated based on neonates with invasive HSV infection whose onset symptoms resembled IBI and the estimated number of Danish neonates who received antibiotics for suspected IBI.

RESULTS

Fifty-four neonates with HSV infection were identified, that is, an incidence of 9 per 100 000 live births. Twenty presented with symptoms resembling IBI, all within the first 14 days of life. Of 18 (78%) neonates, 14 had elevated C reactive protein, 14 of 19 (74%) had elevated alanine aminotransferase and 11 of 17 (65%) had thrombocytopaenia. The estimated NNTs with empiric acyclovir at postnatal ages 0-3, 4-7 and 8-14 days were 1139 (95% CI 523 to 3103), 168 (95% CI 101 to 726) and 117 (95% CI 48 to 198), respectively.

CONCLUSIONS

The incidence of neonatal HSV infection was higher than in previous decades; however, the estimated NNT with empiric acyclovir was high. Therefore, we propose not to treat all neonates suspected of IBI with empiric acyclovir, as current European guidelines suggest. However, HSV should be considered in neonates with signs of infection, especially after the third postnatal day and in neonates with high alanine aminotransferases and thrombocytopaenia.

Less is more: Antibiotics at the beginning of life

Antibiotic exposure at the beginning of life can lead to increased antimicrobial resistance and perturbations of the developing microbiome. Early-life microbiome disruption increases the risks of developing chronic diseases later in life. Fear of missing evolving neonatal sepsis is the key driver for antibiotic overtreatment early in life. Bias (a systemic deviation towards overtreatment) and noise (a random scatter) affect the decision-making process. In this perspective, we advocate for a factual approach quantifying the burden of treatment in relation to the burden of disease balancing antimicrobial stewardship and effective sepsis management.

Group B Streptococcus Early-Onset Disease: New Preventive and Diagnostic Tools to Decrease the Burden of Antibiotic Use

The difficulty in recognizing early-onset neonatal sepsis (EONS) in a timely manner due to non-specific symptoms and the limitations of diagnostic tests, combined with the risk of serious consequences if EONS is not treated in a timely manner, has resulted in a low threshold for starting empirical antibiotic treatment. New guideline strategies, such as the neonatal sepsis calculator, have been proven to reduce the antibiotic burden related to EONS, but lack sensitivity for detecting EONS. In this review, the potential of novel, targeted preventive and diagnostic methods for EONS is discussed from three different perspectives: maternal, umbilical cord and newborn perspectives. Promising strategies from the maternal perspective include Group B Streptococcus (GBS) prevention, exploring the virulence factors of GBS, maternal immunization and antepartum biomarkers. The diagnostic methods obtained from the umbilical cord are preliminary but promising. Finally, promising fields from the newborn perspective include biomarkers, new microbiological techniques and clinical prediction and monitoring strategies. Consensus on the definition of EONS and the standardization of research on novel diagnostic biomarkers are crucial for future implementation and to reduce current antibiotic overexposure in newborns.

Early Empirical Antibiotics and Adverse Clinical Outcomes in Infants Born Very Preterm: A Population-Based Cohort

OBJECTIVE

The objective of this study was to evaluate the association between empirical antibiotic therapy in the first postnatal week in uninfected infants born very preterm and the risk of adverse outcomes until discharge.

STUDY DESIGN

Population-based, nationwide registry study in Norway including all live-born infants with a gestational age <32 weeks surviving first postnatal week without sepsis, intestinal perforation, or necrotizing enterocolitis (NEC) between 2009 and 2018. Primary outcomes were severe NEC, death after the first postnatal week, and/or a composite outcome of severe morbidity (severe NEC, severe bronchopulmonary dysplasia [BPD], severe retinopathy of prematurity, late-onset sepsis, or cystic periventricular leukomalacia). The association between empirical antibiotics and adverse outcomes was assessed using multivariable logistic regression models, adjusting for known confounders.

RESULTS

Of 5296 live-born infants born very preterm, 4932 (93%) were included. Antibiotics were started in first postnatal week in 3790 of 4932 (77%) infants and were associated with higher aOR of death (aOR 9.33; 95% CI: 1.10-79.5, P = .041), severe morbidity (aOR 1.88; 95% CI: 1.16-3.05, P = .01), and severe BPD (aOR 2.17; 95% CI: 1.18-3.98; P = .012), compared with those not exposed. Antibiotics ≥ 5 days were associated with higher odds of severe NEC (aOR 2.27; 95% CI: 1.02-5.06; P = .045). Each additional day of antibiotics was associated with 14% higher aOR of death or severe morbidity and severe BPD.

CONCLUSIONS

Early and prolonged antibiotic exposure within the first postnatal week was associated with severe NEC, severe BPD, and death after the first postnatal week.

Decreased Antibiotic Exposure for Suspected Early-Onset Sepsis in the Neonatal Intensive Care Unit Through Implementation of an Antimicrobial Time-out

Antimicrobials are among the most frequently prescribed drugs in the neonatal intensive care unit (NICU), although most neonates exposed lack a bacterial infection. Overuse of antimicrobials carries risk to the patient and fosters the development of resistant organisms. Strategic and systematic processes hold promise to limit the unnecessary use of these drugs in this population. This study reports a quality improvement initiative in which 2 antimicrobial stewardship strategies were implemented in a large, regional NICU setting: an automatic stop order and an antimicrobial time-out. Antimicrobial use was compared before and after implementation. These 2 simple strategies were associated with a nearly 30% reduction in antibiotic use (31 days per 1000 patient days).

Analysis of Antibiotic Exposure and Early-Onset Neonatal Sepsis in Europe, North America, and Australia

IMPORTANCE

Appropriate use of antibiotics is life-saving in neonatal early-onset sepsis (EOS), but overuse of antibiotics is associated with antimicrobial resistance and long-term adverse outcomes. Large international studies quantifying early-life antibiotic exposure along with EOS incidence are needed to provide a basis for future interventions aimed at safely reducing neonatal antibiotic exposure.

OBJECTIVE

To compare early postnatal exposure to antibiotics, incidence of EOS, and mortality among different networks in high-income countries.

DESIGN, SETTING, AND PARTICIPANTS

This is a retrospective, cross-sectional study of late-preterm and full-term neonates born between January 1, 2014, and December 31, 2018, in 13 hospital-based or population-based networks from 11 countries in Europe and North America and Australia. The study included all infants born alive at a gestational age greater than or equal to 34 weeks in the participating networks. Data were analyzed from October 2021 to March 2022.

EXPOSURES

Exposure to antibiotics started in the first postnatal week.

MAIN OUTCOMES AND MEASURES

The main outcomes were the proportion of late-preterm and full-term neonates receiving intravenous antibiotics, the duration of antibiotic treatment, the incidence of culture-proven EOS, and all-cause and EOS-associated mortality.

RESULTS

A total of 757 979 late-preterm and full-term neonates were born in the participating networks during the study period; 21 703 neonates (2.86%; 95% CI, 2.83%-2.90%), including 12 886 boys (59.4%) with a median (IQR) gestational age of 39 (36-40) weeks and median (IQR) birth weight of 3250 (2750-3750) g, received intravenous antibiotics during the first postnatal week. The proportion of neonates started on antibiotics ranged from 1.18% to 12.45% among networks. The median (IQR) duration of treatment was 9 (7-14) days for neonates with EOS and 4 (3-6) days for those without EOS. This led to an antibiotic exposure of 135 days per 1000 live births (range across networks, 54-491 days per 1000 live births). The incidence of EOS was 0.49 cases per 1000 live births (range, 0.18-1.45 cases per 1000 live births). EOS-associated mortality was 3.20% (12 of 375 neonates; range, 0.00%-12.00%). For each case of EOS, 58 neonates were started on antibiotics and 273 antibiotic days were administered.

CONCLUSIONS AND RELEVANCE

The findings of this study suggest that antibiotic exposure during the first postnatal week is disproportionate compared with the burden of EOS and that there are wide (up to 9-fold) variations internationally. This study defined a set of indicators reporting on both dimensions to facilitate benchmarking and future interventions aimed at safely reducing antibiotic exposure in early life.

Efficacy and safety of switching from intravenous to oral antibiotics (amoxicillin-clavulanic acid) versus a full course of intravenous antibiotics in neonates with probable bacterial infection (RAIN): a multicentre, randomised, open-label, non-inferiority trial

BACKGROUND

Switching from intravenous antibiotic therapy to oral antibiotic therapy among neonates is not yet practised in high-income settings due to uncertainties about exposure and safety. We aimed to assess the efficacy and safety of early intravenous-to-oral antibiotic switch therapy compared with a full course of intravenous antibiotics among neonates with probable bacterial infection.

METHODS

In this multicentre, randomised, open-label, non-inferiority trial, patients were recruited at 17 hospitals in the Netherlands. Neonates (postmenstrual age ≥35 weeks, postnatal age 0-28 days, bodyweight ≥2 kg) in whom prolonged antibiotic treatment was indicated because of a probable bacterial infection, were randomly assigned (1:1) to switch to an oral suspension of amoxicillin 75 mg/kg plus clavulanic acid 18·75 mg/kg (in a 4:1 dosing ratio, given daily in three doses) or continue on intravenous antibiotics (according to the local protocol). Both groups were treated for 7 days. The primary outcome was cumulative bacterial reinfection rate 28 days after treatment completion. A margin of 3% was deemed to indicate non-inferiority, thus if the reinfection rate in the oral amoxicillin-clavulanic acid group was less than 3% higher than that in the intravenous antibiotic group the null hypothesis would be rejected. The primary outcome was assessed in the intention-to-treat population (ie, all patients who were randomly assigned and completed the final follow-up visit on day 35) and the per protocol population. Safety was analysed in all patients who received at least one administration of the allocated treatment and who completed at least one follow-up visit. Secondary outcomes included clinical deterioration and duration of hospitalisation. This trial was registered with ClinicalTrials.gov, NCT03247920, and EudraCT, 2016-004447-36.

FINDINGS

Between Feb 8, 2018 and May 12, 2021, 510 neonates were randomly assigned (n=255 oral amoxicillin-clavulanic group; n=255 intravenous antibiotic group). After excluding those who withdrew consent (n=4), did not fulfil inclusion criteria (n=1), and lost to follow-up (n=1), 252 neonates in each group were included in the intention-to-treat population. The cumulative reinfection rate at day 28 was similar between groups (one [<1%] of 252 neonates in the amoxicillin-clavulanic acid group vs one [<1%] of 252 neonates in the intravenous antibiotics group; between-group difference 0 [95% CI -1·9 to 1·9]; p_{non-inferiority}<0·0001). No statistically significant differences were observed in reported adverse events (127 [50%] vs 113 [45%]; p=0·247). In the intention-to-treat population, median duration of hospitalisation was significantly shorter in the amoxicillin-clavulanic acid group than the intravenous antibiotics group (3·4 days [95% CI 3·0-4·1] vs 6·8 days [6·5-7·0]; p<0·0001).

INTERPRETATION

An early intravenous-to-oral antibiotic switch with amoxicillin-clavulanic acid is non-inferior to a full course of intravenous antibiotics in neonates with probable bacterial infection and is not associated with an increased incidence of adverse events.

FUNDING

The Netherlands Organization for Health Research and Development, Innovatiefonds Zorgverzekeraars, and the Sophia Foundation for Scientific Research.

Association between duration of early empiric antibiotics and necrotizing enterocolitis and late-onset sepsis in preterm infants: a multicenter cohort study

The threshold to initiate empiric antibiotics for suspicion of early-onset sepsis (EOS) is low in preterm infants. Antibiotics' effects on short-term outcomes have recently been debated. We aimed at exploring the extent of early empiric antibiotic exposure (EEAE) in preterm infants and the association between the duration of EEAE with necrotizing enterocolitis (NEC) and late-onset sepsis (LOS) within different EEAE groups. EEAE practice for suspicion of EOS was evaluated in all included infants (gestational age < 30 weeks) born in 9 centers in the Netherlands and Belgium between Oct. 2014 and Jan. 2019. EEAE association with NEC and LOS development was analyzed by multivariate regression. After excluding 56 EOS cases, 1259 infants were included. A total of 1122 infants (89.1%) were exposed to empirical antibiotics for the suspicion of EOS of whom 802 (63.7%) had short (≤ 72 h) and 320 (25.4%) prolonged EEAE (> 72 h). Infants with EEAE ≤ 72 h had a lower incidence of NEC compared to both infants without EEAE (adjusted odds ratio (aOR) 0.39; 95% confidence interval (CI) [0.19-0.80]; p = 0.01) and with prolonged EEAE (> 72 h) (aOR [95%CI]: 0.58 [0.35-0.96]; p = 0.03). With every additional day of EEAE, LOS incidence decreased (aOR [95%CI]: 0.90 [0.85-0.97]; p = 0.003).

CONCLUSION

Almost 90% of preterm infants who have negative blood culture results in the first 72 h of life are exposed to EEAE under suspicion of EOS. One-fourth has prolonged EEAE. Duration of EEAE was differently associated with NEC and LOS incidence. The effects of antibiotics, and potentially induced microbial dysbiosis related to development of NEC and LOS, should further be explored.

WHAT IS KNOWN

• Preterm infants often receive antibiotics empirically directly after birth for suspicion of early-onset sepsis. • The effects of the duration of early empirical antibiotic exposure on the risk for necrotizing enterocolitis and late-onset sepsis are debated.

WHAT IS NEW

• Almost 90% of preterm infants with a gestational age below 30 weeks are exposed to antibiotics empirically after birth despite negative culture results. In a quarter of these culture-negative infants, empirical antibiotics are prolonged. • A short course of empirical antibiotics (≤72h) is associated with decreased odds for necrotizing enterocolitis compared to both prolonged (>72h) or no empirical antibiotics after birth. Furthermore, every additional day of empirical antibiotic exposure is associated with decreased risk for late-onset sepsis in the first month of life.