Antibiotic use among extremely low birth-weight infants from 2009 to 2021: a retrospective observational study.

OBJECTIVE: To assess trends in antibiotic use across a large cohort of extremely low birth-weight (<1000 g; ELBW) infants admitted to academic and community neonatal intensive care units (NICUs) across the USA over a 13-year period. DESIGN: Repeated cross-sectional cohort study. SETTING: Premier Health Database, a comprehensive administrative database of inpatient encounters from academic and community hospitals across the US. PATIENTS: ELBW inborn infants admitted to NICUs from 1 January 2009 to 31 December 2021. INTERVENTIONS: N/A MAIN OUTCOME MEASURES: Absolute and relative changes in (1) proportion of ELBW infants with antibiotic exposure and (2) days of therapy (DOT) per 1000 patient days, over time. Average annual differences were estimated using generalised linear regression with 95% CI. Disposition trends were also measured. RESULTS: Among 36 701 infants admitted to 402 NICUs, the proportion exposed to antibiotics was essentially unchanged (89.9% in 2009 to 89.3% in 2021; absolute reduction of -0.6%); generalised linear regression estimated an annual absolute difference of -0.3% (95% CI (-0.6%) to (-0.07%); p=0.01). DOT per 1000 patient days decreased from 337 in 2009 to 210 in 2021, a 37.8% relative difference and annual relative difference of -4.3% ((-5.2%) to (-3.5%); p<0.001). Mortality was unchanged during the study period. CONCLUSIONS: We found a substantial reduction in antibiotic DOT despite no substantive change in the proportion of infants exposed to antibiotics. This suggests the success of stewardship efforts aimed at antibiotic duration and highlight the need for improved approaches to identifying ELBW infants at highest risk of infection.

Utility of Anaerobic Blood Cultures in Neonatal Sepsis Evaluation.

BACKGROUND: Clinicians variably obtain anaerobic blood cultures as part of sepsis evaluations in the neonatal intensive care unit (NICU). Our objective was to determine if anaerobic blood culture bottles yielded clinically relevant information by either recovering pathogens exclusively or more rapidly than the concurrently obtained aerobic culture bottle in the NICU. METHODS: A retrospective cohort study of blood cultures obtained from infants admitted to the NICU from 08/01/2015-08/31/2023. Standard practice was to inoculate 2 mL of blood divided equally between an aerobic and an anaerobic culture bottle. We analyzed positive blood cultures where both aerobic and anaerobic bottles were obtained and compared pathogen recovery and time to positivity between the bottles. RESULTS: During the study period, 4599 blood cultures were obtained from 3665 infants, and 265 (5.8%) were positive. Of these, 182 cultures were sent as aerobic-anaerobic pairs and recovered pathogenic organisms. Organisms were recovered exclusively from the anaerobic bottle in 32 (17.6%) cultures. Three organisms were obligate anaerobes; the rest were facultative anaerobes including Coagulase-negative staphylococci (40.6%), Escherichia coli (15.6%), and Staphylococcus aureus (15.6%). Cultures with exclusive recovery in the anaerobic bottle were more frequently obtained ≤3 days after birth, compared to other cultures (31.3% vs. 15.3%, p=0.03). When both bottles recovered the pathogen (n=113), the anaerobic bottle had a shorter time to positivity in 76 (67.3%) cultures. CONCLUSIONS: Including anaerobic culture bottles could lead to identification of pathogens not recovered in the aerobic bottle, as well as earlier identification of pathogens.

Antibiotic Stewardship in the Neonatal Intensive Care Unit.

Antibiotic stewardship is a multidisciplinary, evidence-based approach to optimize antibiotic use and mitigate development of antibiotic resistance. Neonates have high rates of antibiotic exposure, particularly those born preterm and admitted to the NICU, and mounting evidence describes the adverse consequences of such exposures in the absence of infection. Here, we review the general principles of antibiotic stewardship and how they can be applied in NICUs. The unique characteristics of NICUs and patients cared for in this setting, which warrant unique implementation strategies and special considerations are discussed. We summarize current antibiotic use metrics for assessment of responses to stewardship interventions and changes over time, and review evidence-based infection prevention practices in the NICU. Current recommendations for empiric antibiotic use in the NICU and the utility of infection biomarkers are summarized. Lastly, given the growing global threat of increasing antibiotic resistance, specific threats in the NICU are highlighted.

Hospital-Onset Bacteremia Among Neonatal Intensive Care Unit Patients.

Importance: The Centers for Disease Control and Prevention plans to introduce hospital-onset bacteremia (HOB) as a health care-associated infection measure. The epidemiology and clinical characteristics of HOB among infants admitted to the neonatal intensive care unit (NICU) are unknown. Objective: To estimate the rate of HOB among infants admitted to the NICU, measure the association of HOB risk with birth weight group and postnatal age, and estimate HOB-attributable mortality. Design, Setting, and Participants: This retrospective multicenter cohort study and emulated trial from 2016 to 2021 included a convenience sample of 322 NICUs in the United States. Participants were infants admitted to participating NICUs for 4 or more days. Exposures: The primary exposures were birth weight and postnatal age. Additional exposures included small for gestational age and central line presence. Main Outcomes and Measures: The primary study outcomes were HOB and HOB-attributable mortality. Results: Of 451 443 included infants, 250 763 (55.6%) were male, 200 680 (44.4%) were female, and 62 091 (13.8%) were born 1500 g or less. Of 9015 HOB events that occurred among 8356 infants (2%) during 8 163 432 days at risk (unadjusted incidence rate, 1.1 per 1000 patient-days; 95% CI, 1.0-1.2), 4888 HOB events (54.2%) occurred in the absence of a central line. Within the first 2 weeks after birth, the HOB rate was 14.2 per 1000 patient-days (95% CI, 12.6-16.1) among infants born 750 g or less, to 0.4 events per 1000 patient-days among infants born more than 2500 g (95% CI, 0.4-0.5). Among infants born 750 g or less, the relative HOB risk decreased by 90% after day 42 compared with days 4 to 14 (incidence rate ratio [IRR], 0.10; 95% CI, 0.1-0.1). Conversely, among infants born more than 2500 g, the relative HOB risk increased by 50% after day 42 compared with days 4 to 14 (IRR, 1.5, 95% CI, 1.2-1.9). Compared with otherwise similar infants without HOB, infants with HOB had an absolute difference in attributable mortality of 5.5% (95% CI, 4.7-6.3). Conclusions and Relevance: This study found that HOB events in the NICU are associated with increased mortality. Birth weight is an important risk factor for HOB; however, the relative rate of HOB decreases over postnatal age among low-birth-weight infants and increases among infants born more than 2500 g. Identifying strategies to prevent HOB and programs to decrease HOB risk are urgently needed to reduce infant mortality.

Trends in C-Reactive Protein Use in Early-onset Sepsis Evaluations and Associated Antibiotic Use.

OBJECTIVE: To determine the prevalence of C-reactive protein (CRP) use in early-onset sepsis (EOS) evaluations in neonatal intensive care units (NICUs) across the US over time and to determine the association between CRP use and antibiotic use. STUDY DESIGN: A retrospective cohort study of NICUs contributing data to Premier Healthcare Database from 2009 through 2021. EOS evaluation was defined as a blood culture charge ≤ 3 days after birth. CRP use for each NICU was calculated as the proportion of infants with a CRP test obtained ≤ 3 days after birth among those undergoing an EOS evaluation and categorized as, low (<25%); medium-low (25 to < 50%), medium-high (50 to < 75%), and high (≥75%). Outcomes included antibiotic use and mortality ≤ 7 days after birth. RESULTS: Among 572 NICUs, CRP use varied widely and was associated with time. The proportion of NICUs with high CRP use decreased from 2009 to 2021 (24.7% vs 17.4%, P < .001), and those with low CRP use increased (47.9% vs 64.8%, P < .001). Compared with low-use NICUs, high-use NICUs more frequently continued antibiotics > 3 days (10% vs 25%, P < .001). This association persisted in multivariable-adjusted regression analyses (adjusted risk ratio 1.95, 95%CI 1.54, 2.48). Risk of mortality was not different in high-use NICUs (adjusted risk difference -0.02%, 95%CI -0.04%, 0.0008%). CONCLUSIONS: CRP use in EOS evaluations varied widely across NICUs. High CRP use was associated with prolonged antibiotic therapy but not mortality ≤ 7 days after birth. Reducing routine CRP use in EOS evaluations may be a target for neonatal antibiotic stewardship efforts.

Perinatal COVID-19: Implications for care of the newborn.

The maternal/newborn dyad presents special challenges to infection management. Early in the COVID-19 pandemic, lack of information regarding SARS-CoV-2 transmission and virulence made it difficult to develop appropriate care guidance when pregnant persons had COVID-19 at the time of presentation for childbirth. We will review the considerations for the parturient, newborn, and care team, and describe the evolution of perinatal COVID management guidance.

Transmission, seroprevalence, and maternal-fetal impact of lymphocytic choriomeningitis virus.

Congenital infections can have devastating short- and long-term impacts on the developing fetus. Lymphocytic choriomeningitis virus (LCMV) is a zoonotic pathogen of concern that causes a severe congenital syndrome but is under-recognized and under-studied. Herein we review data on the natural animal reservoirs of LCMV, modes of transmission to humans, seroprevalence of LCMV worldwide in both pregnant and non-pregnant individuals, mechanisms of viral dissemination to placenta and fetus, and impact of climate change on viral transmission. We highlight opportunities to enhance awareness of congenital LCMV and provide recommendations for prevention and monitoring among at-risk pregnant people. IMPACT: Key message of the article: LCMV is a zoonotic virus that poses a major threat to maternal-fetal health. Adds to the existing literature: We comprehensively address transmission of LCMV from the natural reservoir to the pregnant individual, placenta, and fetus. Impact: Available data call for enhanced patient and provider awareness about congenital LCMV during pregnancy, as well as a need for efforts to better define the seroprevalence and impact of congenital LCMV worldwide.

Antibiotic Use Among Infants Admitted to Neonatal Intensive Care Units.

This cross-sectional study examines antibiotic exposure, days of therapy, types of antibiotics, and changes in use patterns among newborns in neonatal intensive care units (NICUs) across the US from 2009 to 2021.

Critical care among newborns with and without a COVID-19 diagnosis, May 2020-February 2022.

OBJECTIVE: To assess COVID-19 association with newborn critical care outcomes, including nursery level of care and ventilation, during three time periods: Pre-delta (May 2020-June 2021), Delta (July-November 2021), and Omicron (December 2021-February 2022). STUDY DESIGN: In a retrospective cohort of newborns born May 2020-February 2022 using the Premier Healthcare Database, we classified COVID-19 status and critical care using International Classification of Diseases 10th Revision and Current Procedural Terminology codes, laboratory data, and billing records and assessed for variation during three time periods. RESULTS: Of 1,388,712 newborns, 0.06% had COVID-19 during the birth hospitalization (Pre-delta period: 0.03%; Delta: 0.07%; Omicron: 0.21%). Among newborns with COVID-19, the risks for admission to a higher-level nursery and for invasive or non-invasive ventilation were lower in the Omicron period compared to Pre-delta and Delta periods. CONCLUSION: From May 2020-February 2022, COVID-19 in newborns was rare and cases were less severe during the period of Omicron predominance.

Maternal and Newborn Hospital Outcomes of Perinatal SARS-CoV-2 Infection: A National Registry.

OBJECTIVES: The American Academy of Pediatrics National Registry for the Surveillance and Epidemiology of Perinatal coronavirus disease 2019 (COVID-19) (NPC-19) was developed to provide information on the effects of perinatal severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. METHODS: National Registry for the Surveillance and Epidemiology of Perinatal COVID-19 participating centers entered maternal and newborn data for pregnant persons who tested positive for SARS-CoV-2 infection between 14 days before and 10 days after delivery. Incidence of and morbidities associated with maternal and newborn SARS-CoV-2 infection were assessed. RESULTS: From April 6, 2020 to March 19, 2021, 242 centers in the United States centers reported data for 7524 pregnant persons; at the time of delivery, 78.1% of these persons were asymptomatic, 18.2% were symptomatic but not hospitalized specifically for COVID-19, 3.4% were hospitalized for COVID-19 treatment, and 18 (0.2%) died in the hospital of COVID-related complications. Among 7648 newborns, 6486 (84.8%) were tested for SARS-CoV-2, and 144 (2.2%) were positive; the highest rate of newborn infection was observed when mothers first tested positive in the immediate postpartum period (17 of 125, 13.6%). No newborn deaths were attributable to SARS-CoV-2 infection. Overall, 15.6% of newborns were preterm: among tested newborns, 30.1% of polymerase chain reaction-positive and 16.2% of polymerase chain reaction-negative were born preterm (P < .001). Need for mechanical ventilation did not differ by newborn SARS-CoV-2 test result, but those with positive tests were more likely to be admitted to a NICU. CONCLUSIONS: Early in the pandemic, SARS-CoV-2 infection was acquired by newborns at variable rates and without apparent short-term effects. During a period that preceded widespread availability of vaccines, we observed higher than expected numbers of preterm births and maternal in-hospital deaths.

Measles Serostatus Among Parturient Patients at 2 Philadelphia Hospitals in 2021.

This observational study explores whether rubella serostatus, which is routinely assessed during pregnancy, can serve as a proxy for measles serostatus in parturient persons.

Serratia Infection Epidemiology Among Very Preterm Infants in the Neonatal Intensive Care Unit.

BACKGROUND: Serratia spp. are opportunistic, multidrug resistant, Gram-negative pathogens, previously described among preterm infants in case reports or outbreaks of infection. We describe Serratia late-onset infection (LOI) in very preterm infants in a large, contemporary, nationally representative cohort. METHODS: In this secondary analysis of prospectively collected data of preterm infants born 401-1500 grams and/or 22-29 weeks gestational age from 2018 to 2020 at 774 Vermont Oxford Network members, LOI was defined as culture-confirmed blood and/or cerebrospinal fluid infection > 3 days after birth. The primary outcome was incidence of Serratia LOI. Secondary outcomes compared rates of survival and discharge morbidities between infants with Serratia and non-Serratia LOI. RESULTS: Among 119,565 infants, LOI occurred in 10,687 (8.9%). Serratia was isolated in 279 cases (2.6% of all LOI; 2.3 Serratia infections per 1000 infants). Of 774 hospitals, 161 (21%) reported at least one Serratia LOI; 170 of 271 (63%) cases occurred at hospitals reporting 1 or 2 Serratia infections, and 53 of 271 (20%) occurred at hospitals reporting ≥5 Serratia infections. Serratia LOI was associated with a lower rate of survival to discharge compared with those with non-Serratia LOI (adjusted relative risk 0.88, 95% CI: 0.82-0.95). Among survivors, infants with Serratia LOI had higher rates of tracheostomy, gastrostomy and home oxygen use compared with those with non-Serratia LOI. CONCLUSIONS: The incidence of Serratia LOI was 2.3 infections per 1000 very preterm infants in this cohort. Lower survival and significant morbidity among Serratia LOI survivors highlight the need for recognition and targeted prevention strategies for this opportunistic nosocomial infection.

Diagnostic Performance and Patient Outcomes With C-Reactive Protein Use in Early-Onset Sepsis Evaluations.

OBJECTIVES: To determine performance of C-reactive protein (CRP) in the diagnosis of early-onset sepsis, and to assess patient outcomes with and without routine use of CRP. STUDY DESIGN: This was a retrospective cohort study of infants admitted to 2 neonatal intensive care units. CRP was used routinely in early-onset sepsis evaluations during 2009-2014; this period was used to determine CRP performance at a cut-off of ≥10 mg/L in diagnosis of culture-confirmed early-onset sepsis. Routine CRP use was discontinued during 2018-2020; outcomes among infants admitted during this period were compared with those in 2012-2014. RESULTS: From 2009 to 2014, 10 134 infants were admitted; 9103 (89.8%) had CRP and 7549 (74.5%) had blood culture obtained within 3 days of birth. CRP obtained ±4 hours from blood culture had a sensitivity of 41.7%, specificity 89.9%, and positive likelihood ratio 4.12 in diagnosis of early-onset sepsis. When obtained 24-72 hours after blood culture, sensitivity of CRP increased (89.5%), but specificity (55.7%) and positive likelihood ratio (2.02) decreased. Comparing the periods with (n = 4977) and without (n = 5135) routine use of CRP, we observed lower rates of early-onset sepsis evaluation (74.5% vs 50.5%), antibiotic initiation (65.0% vs 50.8%), and antibiotic prolongation in the absence of early-onset sepsis (17.3% vs 7.2%) in the later period. Rate and timing of early-onset sepsis detection, transfer to a greater level of care, and in-hospital mortality were not different between periods. CONCLUSIONS: CRP diagnostic performance was not sufficient to guide decision-making in early-onset sepsis. Discontinuation of routine CRP use was not associated with differences in patient outcomes despite lower rates of antibiotic administration.

Comparison of Maternal and Neonatal Antibody Levels After COVID-19 Vaccination vs SARS-CoV-2 Infection.

Importance: Pregnant persons are at an increased risk of severe COVID-19 from SARS-CoV-2 infection, and COVID-19 vaccination is currently recommended during pregnancy. Objective: To ascertain the association of vaccine type, time from vaccination, gestational age at delivery, and pregnancy complications with placental transfer of antibodies to SARS-CoV-2. Design, Setting, and Participants: This cohort study was conducted in Pennsylvania Hospital in Philadelphia, Pennsylvania, and included births at the study site between August 9, 2020, and April 25, 2021. Maternal and cord blood serum samples were available for antibody level measurements for maternal-neonatal dyads. Exposures: SARS-CoV-2 infection vs COVID-19 vaccination. Main Outcomes and Measures: IgG antibodies to the receptor-binding domain of the SARS-CoV-2 spike protein were measured by quantitative enzyme-linked immunosorbent assay. Antibody concentrations and transplacental transfer ratios were measured after SARS-CoV-2 infection or receipt of COVID-19 vaccines. Results: A total of 585 maternal-newborn dyads (median [IQR] maternal age, 31 [26-35] years; median [IQR] gestational age, 39 [38-40] weeks) with maternal IgG antibodies to SARS-CoV-2 detected at the time of delivery were included. IgG was detected in cord blood from 557 of 585 newborns (95.2%). Among 169 vaccinated persons without SARS-CoV-2 infection, the interval from first dose of vaccine to delivery ranged from 12 to 122 days. The geometric mean IgG level among 169 vaccine recipients was significantly higher than that measured in 408 persons after infection (33.88 [95% CI, 27.64-41.53] arbitrary U/mL vs 2.80 [95% CI, 2.50-3.13] arbitrary U/mL). Geometric mean IgG levels were higher after vaccination with the mRNA-1273 (Moderna) vaccine compared with the BNT162b2 (Pfizer/BioNTech) vaccine (53.74 [95% CI, 40.49-71.33] arbitrary U/mL vs 25.45 [95% CI, 19.17-33.79] arbitrary U/mL; P < .001). Placental transfer ratios were lower after vaccination compared with after infection (0.80 [95% CI, 0.68-0.93] vs 1.06 [95% CI, 0.98-1.14]; P < .001) but were similar between the mRNA vaccines (mRNA-1273: 0.70 [95% CI, 0.55-0.90]; BNT162b2: 0.85 [95% CI, 0.69-1.06]; P = .25). Time from infection or vaccination to delivery was associated with transfer ratio in models that included gestational age at delivery and maternal hypertensive disorders, diabetes, and obesity. Placental antibody transfer was detectable as early as 26 weeks' gestation. Transfer ratio that was higher than 1.0 was present for 48 of 51 (94.1%) births at 36 weeks' gestation or later by 8 weeks after vaccination. Conclusions and Relevance: This study found that maternal and cord blood IgG antibody levels were higher after COVID-19 vaccination compared with after SARS-CoV-2 infection, with slightly lower placental transfer ratios after vaccination than after infection. The findings suggest that time from infection or vaccination to delivery was the most important factor in transfer efficiency.

Late-Onset Sepsis Among Very Preterm Infants.

OBJECTIVES: To determine the epidemiology, microbiology, and associated outcomes of late-onset sepsis among very preterm infants using a large and nationally representative cohort of NICUs across the United States. METHODS: Prospective observational study of very preterm infants born 401 to 1500 g and/or 22 to 29 weeks' gestational age (GA) from January 1, 2018, to December 31, 2020, who survived >3 days in 774 participating Vermont Oxford Network centers. Late-onset sepsis was defined as isolation of a pathogenic bacteria from blood and/or cerebrospinal fluid, or fungi from blood, obtained >3 days after birth. Demographics, clinical characteristics, and outcomes were compared between infants with and without late-onset sepsis. RESULTS: Of 118 650 infants, 10 501 (8.9%) had late-onset sepsis for an incidence rate of 88.5 per 1000 (99% confidence interval [CI] [86.4-90.7]). Incidence was highest for infants born ≤23 weeks GA (322.0 per 1000, 99% CI [306.3-338.1]). The most common pathogens were coagulase negative staphylococci (29.3%) and Staphylococcus aureus (23.0%), but 34 different pathogens were identified. Infected infants had lower survival (adjusted risk ratio [aRR] 0.89, 95% CI [0.87-0.90]) and increased risks of home oxygen (aRR 1.32, 95% CI [1.26-1.38]), tracheostomy (aRR 2.88, 95% CI [2.47-3.37]), and gastrostomy (aRR 2.09, 95% CI [1.93-2.57]) among survivors. CONCLUSIONS: A substantial proportion of very preterm infants continue to suffer late-onset sepsis, particularly those born at the lowest GAs. Infected infants had higher mortality, and survivors had increased risks of technology-dependent chronic morbidities. The persistent burden and diverse microbiology of late-onset sepsis among very preterm infants underscore the need for innovative and potentially organism-specific prevention strategies.

Neonatal Early-Onset Sepsis.

Early-onset sepsis (EOS) is a significant cause of morbidity and mortality among newborn infants, particularly among those born premature. The epidemiology of EOS is changing over time. Here, we highlight the most contemporary data informing the epidemiology of neonatal EOS, including incidence, microbiology, risk factors, and associated outcomes, with a focus on infants born in high-income countries during their birth hospitalization. We discuss approaches to risk assessment for EOS, summarizing national guidelines and comparing key differences between approaches for term and preterm infants. Lastly, we analyze contemporary antibiotic resistance data for EOS pathogens to inform optimal empiric treatment for EOS.

Perinatal COVID-19 maternal and neonatal outcomes at two academic birth hospitals.

OBJECTIVE: Describe 1-month outcomes among newborns of persons with perinatal COVID-19. STUDY DESIGN: Prospective observational study of pregnant persons who tested positive for SARS-CoV-2 between 14 days before and 3 days after delivery and their newborns, from 3/2020 to 3/2021 at two urban high-risk academic hospitals. Phone interviews were conducted to determine 1-month newborn outcomes. RESULTS: Among 9748 pregnant persons, 209 (2.1%) tested positive for perinatal SARS-CoV-2. Symptomatically infected persons were more likely to have a preterm delivery due to worsening maternal condition and their newborns were more likely to test positive for SARS-CoV-2 compared with asymptomatic persons. Six of 191 (3.1%) infants tested were positive for SARS-CoV-2; none had attributable illness before discharge. Of 169 eligible families, 132 (78.1%) participated in post-discharge interviews; none reported their newborn tested positive for SARS-CoV-2 by 1 month of age. CONCLUSION: Symptomatic perinatal COVID-19 had a substantial effect on maternal health but no apparent short-term effect on newborns.

Neonatal infections: Insights from a multicenter longitudinal research collaborative.

For more than 30 years, the Neonatal Research Network (NRN) has conducted studies addressing the epidemiology of neonatal infections, including incidence, microbiology, maternal and neonatal risk factors, associated clinical findings, and outcomes. These studies have provided clinicians and policymakers critical data needed to inform national guidance for infection risk assessment and support daily practice. Further, NRN studies have prompted research into optimal approaches to infection diagnosis, treatment, and antimicrobial stewardship. In this article, we summarize the key findings of NRN infection-related studies, with an emphasis on those published in 2000 or later.

Neighborhood Characteristics and Racial Disparities in Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Seropositivity in Pregnancy.

OBJECTIVE: To quantify the extent to which neighborhood characteristics contribute to racial and ethnic disparities in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seropositivity in pregnancy. METHODS: This cohort study included pregnant patients who presented for childbirth at two hospitals in Philadelphia, Pennsylvania from April 13 to December 31, 2020. Seropositivity for SARS-CoV-2 was determined by measuring immunoglobulin G and immunoglobulin M antibodies by enzyme-linked immunosorbent assay in discarded maternal serum samples obtained for clinical purposes. Race and ethnicity were self-reported and abstracted from medical records. Patients' residential addresses were geocoded to obtain three Census tract variables: community deprivation, racial segregation (Index of Concentration at the Extremes), and crowding. Multivariable mixed effects logistic regression models and causal mediation analyses were used to quantify the extent to which neighborhood variables may explain racial and ethnic disparities in seropositivity. RESULTS: Among 5,991 pregnant patients, 562 (9.4%) were seropositive for SARS-CoV-2. Higher seropositivity rates were observed among Hispanic (19.3%, 104/538) and Black (14.0%, 373/2,658) patients, compared with Asian (3.2%, 13/406) patients, White (2.7%, 57/2,133) patients, and patients of another race or ethnicity (5.9%, 15/256) (P<.001). In adjusted models, per SD increase, deprivation (adjusted odds ratio [aOR] 1.16, 95% CI 1.02-1.32) and crowding (aOR 1.15, 95% CI 1.05-1.26) were associated with seropositivity, but segregation was not (aOR 0.90, 95% CI 0.78-1.04). Mediation analyses revealed that crowded housing may explain 6.7% (95% CI 2.0-14.7%) of the Hispanic-White disparity and that neighborhood deprivation may explain 10.2% (95% CI 0.5-21.1%) of the Black-White disparity. CONCLUSION: Neighborhood deprivation and crowding were associated with SARS-CoV-2 seropositivity in pregnancy in the prevaccination era and may partially explain high rates of SARS-CoV-2 seropositivity among Black and Hispanic patients. Investing in structural neighborhood improvements may reduce inequities in viral transmission.