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Objective This study aimed to estimate the prevalence of measles immunity in a cohort of pregnant women in New York City and determine if there is a positive correlation of measles immunity with patient demographics, rubella immunity, number of measles, mumps, and rubella vaccine (MMR) doses received, and age at last vaccination. Study Design This is a cross-sectional study of pregnant patients seen at a single institution from January 2019 to May 2019. Patients were classified as measles and rubella immune or nonimmune using commercial immunoglobulin G (IgG) tests. Patient characteristics were compared using t-tests, Chi-square tests, or Fisher's exact tests as appropriate. The association of age at last vaccination with immunity status was assessed using multivariable logistic regression adjusted for age at presentation. The utility of rubella IgG for distinguishing measles immunity was assessed using receiver operating characteristic curve analysis. Results Serologic immunity for measles and rubella was obtained for 1,366 patients. Of these, 1,047 (77%) were measles immune and 1,291 (95%) were rubella immune. Patients born after 1989 were less likely to be immune to measles, while multiparity and private insurance were associated with increased measles immunity. Documentation of MMR vaccination was available for 140 (10%) patients. Of these, 44 (31%) were serologically nonimmune to measles and 9 (6.4%) were nonimmune to rubella. In patients known to have received one dose of MMR, 62% (24/39) were immune to measles with an improvement to 72% (69/96) among those who received two or more doses. Age at last vaccination was not associated with measles immunity. Rubella IgG level was a poor predictor of positive measles titer (area under the curve = 0.59). Conclusion Approximately one of every four pregnant patients is serologically measles nonimmune, even among women with documented MMR vaccination or documented rubella immunity. These findings raise concerns that relying on vaccination history or rubella immune status may not be sufficient to assure protection from infection with measles. If further suggests that measles serology should be added to routine prenatal laboratory testing to identify nonimmune patients that may benefit from postpartum vaccination. Key Points

Background Intra-partum (IP) IV vancomycin (VAN) 20 mg/kg every 8 hours is proposed by #797 for the prevention of early onset neonatal group B streptococcal disease (GBS), a recommendation for which the basis of scientific merit is poor. The goal of our study was to analyze the sparsely sampled published data and raise awareness about the underlying risk of VAN toxicity with this dosing approach. Methods Plasma and cord-blood concentration-time data of IV VAN given to mothers in the IP period was analyzed. 5000 Monte Carlo runs were conducted to simulate maternal/fetal exposure (AUC0-24; 24-48) for doses of 1500, 1750 and 2000 mgs q8h and for possible birth times at two-hour intervals. Neonatal VAN clearance was not possible to determine; hence, we used a validated PK model to calculate exposure for the first 24h of life for gestational ages (GA) of 33 to 40 weeks. The AUC range of 400 – 600, and > 600 mg*h/L were considered for indices of efficacy and toxicity, respectively. Results Estimates from 30 pairs of serum and cord-blood concentrations analyzed with a 2-compartment model are shown in Table 1. Maternal VAN exposures seem acceptable up to 2 IP doses given with mean (SD) AUC0-24 of 394 (140), 474 (167), and 540 (193) mg*h/L for the 1500, 1750 and 2000 mg regimens. Most mothers (up to 83%) who receive three or more doses will be subjected to nephrotoxic exposures (Figure 1.). Neonatal evaluations indicate similarly low PTAs for the three dosing regimens when the efficacy target is considered (Figure 2. A). On the other hand, the PTAs for potentially nephrotoxic exposure is expected to reach undesirable levels when three or more doses were to be administered. The risk is profoundly high in GA of 33 to 35 weeks and birth times beyond 20 hours after the initiation of intra-partum prophylaxis (Figure 2. B). Figure 1. Figure 2.A Figure 2.B Conclusion Current recommendations by #797 for dosing of vancomycin pose significant risk to mother and newborn alike, especially in cases with lengthy duration of labor. Based on our results, maternal therapeutic drug monitoring for all cases requiring more than two doses should be considered. With the proposed dosing regimen going un-adjusted, 1 out of 4 newborns and 4 out of 5 mothers may be subjected to nephrotoxic exposures in prolonged labor. Table 1. Disclosures All Authors: No reported disclosures

Background Countless diseases and medications have been implicated in the past as causing prolongation of the QT interval. Their unique role through the means of quantifying the definite magnitude of relative risk they contribute during hospitalization still requires further investigation. The aim of this study was to describe the impact of commonly used anti-infectives on the QT interval in hospitalized patients during the COVID-19 era. Methods Demographic information, medical history, laboratory data, medication administration history and ECG recording data was collected from the electronic records of adult patients admitted to two urban hospitals. A mixed effects approach with four sub-models for the QT interval comprised of: heart rate, circadian rhythm, gender, and the drug (regressed as the cumulative mg dose administered over time) and disease effects was used. Fixed and random effects with between occasion variability were estimated for the parameters with a Bayesian approach using the STAN software. Results Data from 2180 patients were used with baseline characteristics shown in Table 1. Observed vs. predicted plots based on the training (Figure 1.A) and validation data set (Figure 1.B) showed excellent fit. The parameters for QTc0, α, gender, and circadian rhythm were identified within the range previously described (Table 2.). Similarly, the model correctly identified the impact of acute or chronic diseases on the QT interval. Model coefficient estimates [mean (95% CI) of 0.010 (0.006, 0.15) and 0.0045 (0.0013, 0.01100) msec/mg cumulative dose, respectively] suggest that patients treated with conventional regimens of fluconazole and levofloxacin are most likely to present with a QT interval increase > 5 msec, the cutoff threshold of regulatory concern. Figure 1. A-B Table 1. Table 2. Conclusion The model developed accurately identified the impact baseline risk factors and concomitant medications have on the QT interval. When adjusted for these confounding variables, estimates of QT interval prolongation show that treatment with fluconazole and levofloxacin pose a considerable risk; while treatment with azithromycin or hydroxychloroquine is of moderate risk for QT interval prolongation. Disclosures All Authors: No reported disclosures

Background Torsades de pointes is a life-threatening ventricular tachycardia associated with prolongation of the QT interval. Many diseases and medications have been implicated as potentially prolonging the QT interval, but little data exists regarding the means of quantifying this risk. The aim of this study was to describe the impact of commonly used antimicrobials on the QT interval in hospitalized patients. Methods Demographic, diseases, laboratory, medication administration history and ECG recording data were collected from the electronic records of adult patients admitted, from July 2018 to December 2018, to two urban hospitals. A model for the QT interval comprised of four sub-models: gender, heart rate, circadian rhythm, and the drug and disease effects. Fixed and random effects with between occasion variability were estimated for the parameters. A Bayesian approach using the NUTS in STAN was used via the brms package in the R® software. Results Data from 1,353 patients were used with baseline characteristics shown in Table 1. Observed vs. predicted plots based on the training (Figure 1A) and validation data set (Figure 1B) showed a great fit. The parameters for QTc0, α, gender, and circadian rhythm were accurately identified (Table 2). Similarly, the model correctly described the expected impact of acute or chronic diseases on the QT interval. Uncertainty interval estimates (Figure 2) show that patients treated with fluconazole and levofloxacin are likely to present with a QT interval [mean (95% CI) of 6.84 (0.22,21.45) and 5.05 (0.15, 16.70), respectively], that is > 5 ms longer vs. no treatment, the minimum cutoff that should evoke further risk assessment of QT interval prolongation. Conclusion The model developed correctly describes the impact baseline risk factors have on the QT interval. Point estimates of QT interval prolongation show that patients treated with fluconazole and levofloxacin may be at considerable risk; while those treated with azithromycin or ciprofloxacin are more likely to be at an insignificant risk for QT interval prolongation during hospital admission. Further workup to quantify the impact of concomitant treatment with these and other at-risk medications is underway. Disclosures All authors: No reported disclosures.

We performed a nested case-control study (ratio of 1:4) on the emergence of tigecycline-resistant multidrug-resistant Klebsiella pneumoniae (TR-MDRKP) isolates among patients who initially presented with a tigecycline-susceptible MDRKP isolate. Out of 260 patients, 24 (9%) had a subsequent clinical culture positive for a TR-MDRKP isolate within the 90-day follow-up period. On logistic regression analyses, receipt of tigecycline (adjusted odds ratio [OR], 5.06; 95% confidence interval [CI], 1.80 to 14.23; P = 0.002) was the only independent predictor of subsequent isolation of a TR strain.