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Background: Faculty perceptions of medical student knowledge are often based on case presentations, but their assessment of student performance can vary significantly based on content, presentation skill, and interpersonal characteristics. Purpose: To determine if a brief faculty development intervention could significantly decrease (>/= 20%) faculty members' variability in rating student case presentations in the ambulatory setting. Methods: During the 1998-99 academic year, we videotaped 10 third-year medical students during one well-child presentation. Seven general pediatric faculty rated the videotapes using a validated scoring instrument measuring content: History of Present Illness (HPI), Past Medical History, and Physical Exam (PE); and communication skill: Precision of Language, Fluency, and Economy. Baseline ratings were from June to September 1999 and then repeated in October to November 2000 following a workshop where faculty reflected on the rating process and decreasing rating variance. The change in mean faculty ratings of the student's overall performance and for each item and the change in the mean difference in standard deviation before and after the workshop were analyzed. Results: Internal consistency of the scoring instrument using Cronbach's alpha was 0.88. The mean faculty rating for overall presentation performance and the PE did not significantly change after the workshop, whereas for all other items it did. The mean standard deviation of faculty ratings decreased significantly for the overall performance and all other items except HPI. Conclusion: Despite using a validated scoring instrument to rate student case presentations significant variability exists among faculty, with rating inflation likely. A brief faculty development intervention using 'reflection-on-action' was associated with more congruent ratings in the short term. [ABSTRACT FROM AUTHOR]

Background: Prenatal Zika virus (ZIKV) infection leads to microcephaly and adverse neurodevelopment. The effects of postnatal ZIKV infection on the developing brain are unknown. We assessed the neurodevelopmental outcomes of children exposed postnatally during the ZIKV epidemic., Methods: A prospective study enrolled infants 0-3 months of age and their mothers, and children 1.5-3.5 years of age in rural Guatemala from 2017 and were followed for 12 months until 2019. Neurodevelopment was evaluated using the Mullen Scales of Early Learning (MSEL). ZIKV and dengue virus (DENV) infections were identified by polymerase chain reaction (PCR) using active surveillance. Serological analyses, stratified by age group flavivirus serostatus at enrollment, were conducted using a focus reduction neutralization test., Results: Of 1371 enrolled participants, 1187 (86.6%) completed the study. No PCR-confirmed ZIKV infections were identified during the study period. One-third of 1.5-3.5-year-old children were ZIKV-seropositive at enrollment (likely postnatal infection). Twenty participants (5.8%) tested positive for DENV by PCR (11 infants, 5 children and 4 mothers); 15 (75%) were DENV-3 infections and 5 were DENV-2. The incidence of DENV infection in infants was 2.6%. No significant differences in MSEL scores were found between infants born seropositive versus seronegative for ZIKV or DENV. DENV seropositivity at enrollment in 1.5-5-year-old children was associated with lower MSEL scores for fine motor, visual reception and language, and microcephaly at 12 months versus seronegative children (all P < 0.05)., Conclusions: Postnatal ZIKV infection in children from rural Guatemala was not associated with worse neurodevelopmental outcomes. DENV seropositivity was associated with a higher risk of microcephaly in infants and worse neurodevelopmental outcomes in children., Competing Interests: E.J.A. has served on safety monitoring and advisory boards for Moderna, Hillevax, Inovio, Sanofi and Merck, and his institution receives funds to conduct clinical research unrelated to this manuscript from Pfizer, Biofire, and Roche. F.M.M. has served on safety monitoring and advisory boards for Moderna, Pfizer, Sanofi, Aztra Zeneca and Merck and has conducted research funded by the US Centers for Disease Control and Prevention, Pfizer, Gilead. D.O. has received research support from Roche. Other authors have no conflicts of interest to disclose., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)

Background: Although antivirals remain important for the treatment COVID-19, methods to assess treatment efficacy are lacking. Here, we investigated the impact of remdesivir on viral dynamics and their contribution to understanding antiviral efficacy in the multicenter Adaptive COVID-19 Treatment Trial 1, which randomized patients to remdesivir or placebo., Methods: Longitudinal specimens collected during hospitalization from a substudy of 642 patients with COVID-19 were measured for viral RNA (upper respiratory tract and plasma), viral nucleocapsid antigen (serum), and host immunologic markers. Associations with clinical outcomes and response to therapy were assessed., Results: Higher baseline plasma viral loads were associated with poorer clinical outcomes, and decreases in viral RNA and antigen in blood but not the upper respiratory tract correlated with enhanced benefit from remdesivir. The treatment effect of remdesivir was most pronounced in patients with elevated baseline nucleocapsid antigen levels: the recovery rate ratio was 1.95 (95% CI, 1.40-2.71) for levels >245 pg/mL vs 1.04 (95% CI, .76-1.42) for levels <245 pg/mL. Remdesivir also accelerated the rate of viral RNA and antigen clearance in blood, and patients whose blood levels decreased were more likely to recover and survive., Conclusions: Reductions in SARS-CoV-2 RNA and antigen levels in blood correlated with clinical benefit from antiviral therapy., Clinical Trial Registration: NCT04280705 (ClinicalTrials.gov)., Competing Interests: Potential conflicts of interest . A. L. G. reports contract testing to his institution from Abbott, Cepheid, Novavax, Pfizer, Janssen, and Hologic and research support to his institution from Gilead Sciences, Inc, and Merck outside of the described work. D. P. is an employee and shareholder of Gilead Sciences, Inc. K. J. is a shareholder of and was employed by Gilead Sciences, Inc, at the time of manuscript development. C. A. B. has received grants/contracts to her institution from Gilead Sciences, Inc, and consultant fees from NDA Partners, LLC, related to drug development. C. A. B. served as the president of the CROI Foundation Board of Directors, vice president of the Zimbabwe AIDS Treatment Assistance Project Board of Directors, and secretary/treasurer of the IAS-USA Board of Directors (all nonprofit organizations). C. A. B. recently served as deputy editor for Clinical Infectious Diseases for the Infectious Diseases Society of America. N. J. reports salary support by Sagent Pharmaceuticals to his institution. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest., (Published by Oxford University Press on behalf of Infectious Diseases Society of America 2024.)

Zika virus (ZIKV) is a flavivirus primarily transmitted by Aedes species mosquitoes, first discovered in Africa in 1947, that disseminated through Southeast Asia and the Pacific Islands in the 2000s. The first ZIKV infections in the Americas were identified in 2014, and infections exploded through populations in Brazil and other countries in 2015/16. ZIKV infection during pregnancy can cause severe brain and eye defects in offspring, and infection in adults has been associated with higher risks of Guillain-Barré syndrome. We initiated a study to describe the natural history of Zika (the disease) and the immune response to infection, for which some results have been reported. In this paper, we identify ZIKV-specific CD4+ and CD8+ T cell epitopes that induce responses during infection. Two screening approaches were utilized: an untargeted approach with overlapping peptide arrays spanning the entire viral genome, and a targeted approach utilizing peptides predicted to bind human MHC molecules. Immunoinformatic tools were used to identify conserved MHC class I supertype binders and promiscuous class II binding peptide clusters predicted to bind 9 common class II alleles. T cell responses were evaluated in overnight IFN-γ ELISPOT assays. We found that MHC supertype binding predictions outperformed the bulk overlapping peptide approach. Diverse CD4+ T cell responses were observed in most ZIKV-infected participants, while responses to CD8+ T cell epitopes were more limited. Most individuals developed a robust T cell response against epitopes restricted to a single MHC class I supertype and only a single or few CD8+ T cell epitopes overall, suggesting a strong immunodominance phenomenon. Noteworthy is that many epitopes were commonly immunodominant across persons expressing the same class I supertype. Nearly all of the identified epitopes are unique to ZIKV and are not present in Dengue viruses. Collectively, we identified 31 immunogenic peptides restricted by the 6 major class I supertypes and 27 promiscuous class II epitopes. These sequences are highly relevant for design of T cell-targeted ZIKV vaccines and monitoring T cell responses to Zika virus infection and vaccination., Competing Interests: MM reported laboratory research and clinical trials contract funding with Lilly, Pfizer, and Sanofi; and personal fees for Scientific Advisory Board service from Merck, Meissa Vaccines, Inc. and Pfizer. Authors FT, AG, WM, LM, and ADG are (or were) employed by EpiVax, Inc, and author CF was employed by The Emmes Company, LLC. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Eickhoff, Meza, Terry, Colbert, Blazevic, Gutiérrez, Stone, Brien, Pinto, El Sahly, Mulligan, Rouphael, Alcaide, Tomashek, Focht, Martin, Moise, De Groot and Hoft.)

Background: We evaluated the burden of Shigella spp from children aged 0-59 months with medically attended moderate-to-severe diarrhea and matched controls at sites in Mali, The Gambia, and Kenya participating in the Vaccine Impact on Diarrhea in Africa (VIDA) study from 2015 to 2018., Methods: Shigella spp were identified using coprocultures and serotyping in addition to quantitative polymerase chain reaction (qPCR). Episode-specific attributable fractions (AFe) for Shigella were calculated using Shigella DNA quantity; cases with AFe ≥0.5 were considered to have shigellosis., Results: The prevalence of Shigella was determined to be 359 of 4840 (7.4%) cases and 83 of 6213 (1.3%) controls by culture, and 1641 of 4836 (33.9%) cases and 1084 of 4846 (22.4%) controls by qPCR (cycle threshold <35); shigellosis was higher in The Gambia (30.8%) than in Mali (9.3%) and Kenya (18.7%). Bloody diarrhea attributed to Shigella was more common in 24- to 59-month-old children (50.1%) than 0- to 11-month-old infants (39.5%). The Shigella flexneri serogroup predominated among cases (67.6% of isolates), followed by Shigella sonnei (18.2%), Shigella boydii (11.8%), and Shigella dysenteriae (2.3%). The most frequent S. flexneri serotypes were 2a (40.6%), 1b (18.8%), 6 (17.5%), 3a (9.0%), and 4a (5.1%). Drug-specific resistance among 353 (98.3%) Shigella cases with AMR data was as follows: trimethoprim-sulfamethoxazole (94.9%), ampicillin (48.4%), nalidixic acid (1.7%), ceftriaxone (0.3%), azithromycin (0.3%), and ciprofloxacin (0.0%)., Conclusions: A high prevalence of shigellosis continues in sub-Saharan Africa. Strains are highly resistant to commonly used antibiotics while remaining susceptible to ciprofloxacin, ceftriaxone, and azithromycin., Competing Interests: Potential conflicts of interest. K. L. K. reports consultation fees and travel support from PATH and the University of Washington related to diarrheal diseases and grant support to her institution from the National Institutes of Health, Institut Pasteur, and the Bill & Melinda Gates Foundation. M.-A. W. reports receiving funding from the CDC and the Institute of Tropical Medicine. S. M. T. reports multiple grants (paid to institution) from the National Institutes of Health, Bill & Melinda Gates Foundation, Wellcome Trust, Affinivax, Lumen Biosciences, PATH, and Medical Research Council; payments as royalties related to intellectual property for Salmonella vaccines and Klebsiella/Pseudomonas vaccines; consulting fees and travel support from the University of Washington for a grant proposal; multiple planned, issued, and pending patents on Salmonella, Klebsiella, and Pseudomonas vaccines; and multiple unpaid committee roles with the American Society of Tropical Medicine and Hygiene. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (© The Author(s) 2023. Published by Oxford University Press on behalf of Infectious Diseases Society of America.)

Background: Diagnosis of pneumonia remains challenging. Digitally recorded and remote human classified lung sounds may offer benefits beyond conventional auscultation, but it is unclear whether classifications differ between the two approaches. We evaluated concordance between digital and conventional auscultation., Methods: We collected digitally recorded lung sounds, conventional auscultation classifications and clinical measures and samples from children with pneumonia (cases) in low-income and middle-income countries. Physicians remotely classified recordings as crackles, wheeze or uninterpretable. Conventional and digital auscultation concordance was evaluated among 383 pneumonia cases with concurrently (within 2 hours) collected conventional and digital auscultation classifications using prevalence-adjusted bias-adjusted kappa (PABAK). Using an expanded set of 737 cases that also incorporated the non-concurrently collected assessments, we evaluated whether associations between auscultation classifications and clinical or aetiological findings differed between conventional or digital auscultation using χ 2 tests and logistic regression adjusted for age, sex and site., Results: Conventional and digital auscultation concordance was moderate for classifying crackles and/or wheeze versus neither crackles nor wheeze (PABAK=0.50), and fair for crackles-only versus not crackles-only (PABAK=0.30) and any wheeze versus no wheeze (PABAK=0.27). Crackles were more common on conventional auscultation, whereas wheeze was more frequent on digital auscultation. Compared with neither crackles nor wheeze, crackles-only on both conventional and digital auscultation was associated with abnormal chest radiographs (adjusted OR (aOR)=1.53, 95% CI 0.99 to 2.36; aOR=2.09, 95% CI 1.19 to 3.68, respectively); any wheeze was inversely associated with C-reactive protein >40 mg/L using conventional auscultation (aOR=0.50, 95% CI 0.27 to 0.92) and with very severe pneumonia using digital auscultation (aOR=0.67, 95% CI 0.46 to 0.97). Crackles-only on digital auscultation was associated with mortality compared with any wheeze (aOR=2.70, 95% CI 1.12 to 6.25)., Conclusions: Conventional auscultation and remotely-classified digital auscultation displayed moderate concordance for presence/absence of wheeze and crackles among cases. Conventional and digital auscultation may provide different classification patterns, but wheeze was associated with decreased clinical severity on both., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2022. Re-use permitted under CC BY. Published by BMJ.)

Background: Vaccination is the primary strategy to reduce influenza burden. Influenza vaccine effectiveness (VE) can vary annually depending on circulating strains., Methods: We used a test-negative case-control study design to estimate influenza VE against laboratory-confirmed influenza-related hospitalizations among children (aged 6 months-17 years) across 5 influenza seasons in Atlanta, Georgia, from 2012-2013 to 2016-2017. Influenza-positive cases were randomly matched to test-negative controls based on age and influenza season in a 1:1 ratio. We used logistic regression models to compare odds ratios (ORs) of vaccination in cases to controls. We calculated VE as [100% × (1 - adjusted OR)] and computed 95% confidence intervals (CIs) around the estimates., Results: We identified 14 596 hospitalizations of children who were tested for influenza using the multiplex respiratory molecular panel; influenza infection was detected in 1017 (7.0%). After exclusions, we included 512 influenza-positive cases and 512 influenza-negative controls. The median age was 5.9 years (interquartile range, 2.7-10.3), 497 (48.5%) were female, 567 (55.4%) were non-Hispanic Black, and 654 (63.9%) children were unvaccinated. Influenza A accounted for 370 (72.3%) of 512 cases and predominated during all 5 seasons. The adjusted VE against influenza-related hospitalizations during 2012-2013 to 2016-2017 was 51.3% (95% CI, 34.8% to 63.6%) and varied by season. Influenza VE was 54.7% (95% CI, 37.4% to 67.3%) for influenza A and 37.1% (95% CI, 2.3% to 59.5%) for influenza B., Conclusions: Influenza vaccination decreased the risk of influenza-related pediatric hospitalizations by >50% across 5 influenza seasons., (© The Author(s) 2021. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Objectives: To understand the epidemiology of acute hematogenous osteomyelitis and septic arthritis, including clinical and demographic features, microbiology, treatment approaches, treatment-associated complications, and outcomes., Study Design: Retrospective cohort study of 453 children with acute hematogenous osteomyelitis and/or septic arthritis from 2009 to 2015., Results: Among the 453 patients, 218 (48%) had acute hematogenous osteomyelitis, 132 (29%) had septic arthritis, and 103 (23%) had concurrent acute hematogenous osteomyelitis/septic arthritis. Treatment failure/recurrent infection occurred in 41 patients (9%). Patients with concurrent acute hematogenous osteomyelitis/septic arthritis had longer hospital stays, longer duration of antibiotic therapy, and were more likely to have prolonged bacteremia and require intensive care. Staphylococcus aureus was identified in 228 (51%) patients, of which 114 (50%) were methicillin-resistant S aureus. Compared with septic arthritis, acute hematogenous osteomyelitis and concurrent acute hematogenous osteomyelitis/septic arthritis were associated with higher odds of treatment failure (OR, 8.19; 95% CI, 2.02-33.21 [P = .003]; and OR, 14.43; 95% CI, 3.39-61.37 [P < .001], respectively). The need for more than 1 surgical procedure was also associated with higher odds of treatment failure (OR, 2.98; 95% CI, 1.18-7.52; P = .021). Early change to oral antibiotic therapy was not associated with treatment failure (OR, 0.64; 95% CI, 0.24-1.74; P = .386). Most (73%) medically attended treatment complications occurred while on parenteral therapy., Conclusions: Musculoskeletal infections are challenging pediatric infections. S aureus remains the most common pathogen, with methicillin-resistant S aureus accounting for 25% of all cases. Concurrent acute hematogenous osteomyelitis/septic arthritis is associated with more severe disease and worse outcomes. Fewer treatment-related complications occurred while on oral therapy. Early transition to oral therapy was not associated with treatment failure., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Background: Whether digitally recorded lung sounds are associated with radiographic pneumonia or clinical outcomes among children in low-income and middle-income countries is unknown. We sought to address these knowledge gaps., Methods: We enrolled 1 to 59monthold children hospitalized with pneumonia at eight African and Asian Pneumonia Etiology Research for Child Health sites in six countries, recorded digital stethoscope lung sounds, obtained chest radiographs, and collected clinical outcomes. Recordings were processed and classified into binary categories positive or negative for adventitial lung sounds. Listening and reading panels classified recordings and radiographs. Recording classification associations with chest radiographs with World Health Organization (WHO)-defined primary endpoint pneumonia (radiographic pneumonia) or mortality were evaluated. We also examined case fatality among risk strata., Results: Among children without WHO danger signs, wheezing (without crackles) had a lower adjusted odds ratio (aOR) for radiographic pneumonia (0.35, 95% confidence interval (CI): 0.15, 0.82), compared to children with normal recordings. Neither crackle only (no wheeze) (aOR: 2.13, 95% CI: 0.91, 4.96) or any wheeze (with or without crackle) (aOR: 0.63, 95% CI: 0.34, 1.15) were associated with radiographic pneumonia. Among children with WHO danger signs no lung recording classification was independently associated with radiographic pneumonia, although trends toward greater odds of radiographic pneumonia were observed among children classified with crackle only (no wheeze) or any wheeze (with or without crackle). Among children without WHO danger signs, those with recorded wheezing had a lower case fatality than those without wheezing (3.8% vs. 9.1%, p = .03)., Conclusions: Among lower risk children without WHO danger signs digitally recorded wheezing is associated with a lower odds for radiographic pneumonia and with lower mortality. Although further research is needed, these data indicate that with further development digital auscultation may eventually contribute to child pneumonia care., (© 2020 The Authors. Pediatric Pulmonology published by Wiley Periodicals LLC.)

Filociclovir (MBX-400, cyclopropavir) is an antiviral agent with activity against cytomegalovirus (CMV). A phase 1, double-blind, randomized, placebo-controlled (3:1 ratio), single-center, multiple-ascending-dose trial was conducted to assess the safety, tolerability, and pharmacokinetics of filociclovir. Filociclovir ( n  = 18) or placebo ( n  = 6) was administered as a daily oral dose (100 mg, 350 mg, or 750 mg) for 7 days to normal healthy adults (ages, 25 to 65 years) who were monitored for 22 days. Safety assessments included clinical, laboratory, and electrocardiogram monitoring. Plasma and urine samplings were used to determine pharmacokinetic parameters. All study product-related adverse events were mild, most commonly gastrointestinal (17%), nervous system (11%), and skin and subcutaneous tissue (11%) disorders. One subject had reversible grade 3 elevation in serum creatinine and bilirubin, which was associated with an ∼1-log increase in plasma filociclovir exposure compared to levels for other subjects in the same (750-mg) cohort. No other serious adverse events were observed. Plasma exposures (area under the concentration-time curve from 0 to 24 h [AUC 0-24 ]) on days 1 and 7 were similar, suggesting negligible dose accumulation. There was a sublinear increase in plasma exposure with dose, which plateaued at the daily dose of 350 mg. The amount of filociclovir recovered in the urine remained proportional to plasma exposure (AUC). Doses as low as 100 mg achieved plasma concentrations sufficient to inhibit CMV in vitro (This study has been registered at ClinicalTrials.gov under identifier NCT02454699.)., (Copyright © 2019 American Society for Microbiology.)

Background: Maternal GBS colonization is associated with early-onset neonatal sepsis and extensive efforts are directed to preventing this complication. Less is known about maternal risks of GBS colonization. We seek to provide a modern estimate of the incidence and impact of maternal GBS colonization and invasive GBS disease., Methods: A single center historical cohort study of all births between 2003 and 2015 was performed. Data was collected via electronic health record abstraction using an institutional specific tool. Descriptive statistics were performed regarding GBS status. Inferential statistics were performed comparing risk of adverse pregnancy outcomes in cohorts with and without GBS colonization as well as cohorts with GBS colonization and invasive GBS disease., Results: A total of 60,029 deliveries were included for analysis. Overall, 21.6% of the population was GBS colonized and 0.1% had invasive GBS disease. GBS colonization was associated with younger maternal age, Black race, non-Hispanic ethnicity, chronic hypertension, preexisting diabetes, and tobacco use (p<0.01). In the adjusted analyses, there was an increased risk of gestational diabetes (aRR 1.21, 95% CI 1.11-1.32) in colonized pregnancies and a decreased incidence of short cervix (aRR 0.64, 95% CI 0.52-0.79), chorioamnionitis (aRR 0.76, 95% CI 0.66-0.87), wound infection (aRR 0.75, 95% CI 0.64-0.88), and operative delivery (aRR 0.85, 95% CI 0.83-0.88)., Conclusions: This modern-day large cohort of all births over a 12-year period demonstrates a GBS colonization rate of 21.6%. This data reflects a need to assess maternal and perinatal outcomes in addition to neonatal GBS sepsis rates to inform decisions regarding the utility of maternal vaccination.

The Mehlich 3 (M3) method is widely used for extraction of plant-available phosphorus (P) from soil over a wide range of pH values. The method is also used by many laboratories to determine multiple plant-available nutrients simultaneously. However, this method has not been statistically validated within and among laboratories. The objective of this study was to determine the repeatability (within-laboratory performance) and reproducibility (among-laboratories performance) of the M3 method by using a wide variety of soils. An in-house homogeneity test was conducted for 10 soils. Three replicates of each of the 10 soils were sent to 26 domestic and international laboratories primarily for P analysis. Samples were scooped, weighed, or both scooped and weighed for extraction. The P in extracts was quantified by the participating laboratories by using inductively coupled plasma-atomic emission spectrometry (ICP-AES) or colorimetrically. For the scooped samples analyzed colorimetrically, the repeatability relative standard deviation (RSDr) ranged from 2.07 to 12.1%; the RSDr ranged from 2.2 to 21.4% for the scooped samples analyzed by ICP-AES. For the weighed samples analyzed colormetrically, the RSDr values were 1.09-9.34%, and for the weighed samples analyzed by ICP-AES, they were 1.70-5.76%. For the reproducibility data, the RSDR values ranged from 6.85 to 50.8% for the scooped-colorimetry category, from 6.95 to 73.9% for the scooped-ICP-AES category, from 7.19 to 42.6% for the weighed-colorimetry category, and from 5.29 to 35.9% for the weighed-ICP-AES category. The greatest RSD values were associated with the Susitna soil, which had the smallest concentration of extractable P. Because of the relatively small concentration of P in this soil, the laboratories were attempting to measure solution concentrations that were close to the detection limits. The Horwitz ratios (HorRat) were also used to evaluate the repeatability, HorRat(r), and reproducibility, HorRat(R). Overall, the M3 P method appears to be both repeatable and reproducible across the 4 categories, and the vast majority of the HorRat values for both repeatability and reproducibility were within the acceptable range. The results of this study indicate that the M3 P method for the determination of plant-available P in soil is both accurate and precise when standardized procedures are used. The method has been shown to be suitable for use as a reference method for testing soil materials for extractable P.

A liquid chromatographic (LC) method for the analysis of lasalocid sodium in premixes, complete animal feeds, and trace-level feeds was collaboratively studied. The method employs a 0.5% HCI acidified methanol extraction followed by 20 min sonication in a water bath heated to 40 degrees C. Samples are then shaken on a mechanical shaker for 1 h and stored overnight, followed by an additional 10 min shaking the following morning. Sample extracts are diluted if necessary with extractant, filtered, and injected onto an LC system. Determination of all lasalocid homologs is by reversed-phase LC with fluorescence detection at 314 nm excitation and 418 nm emission. Eight samples of drug premixes, medicated feeds, and mineral supplements, along with 2 samples for trace-level analysis were sent to 20 collaborators in the United States, Canada, and The Netherlands. Study data were returned by 17 laboratories. Two additional supplemental trace-level samples and a blank feed were provided to 15 of the collaborating laboratories, and test data were received from all 15 participants. For the drug premixes, medicated feeds, and mineral supplements, RSDr values (within-laboratory repeatability) ranged from 1.2 to 19.9%, RSDR values (among-laboratory reproducibility) ranged from 3.4 to 32.3%, and HorRat values ranged from 0.35 to 3.73. For the trace-level samples, only lasalocid A, the predominant homolog comprising > 90% of the sum of all homolog peak area, was quantified. All laboratories correctly identified the analyte. Although some instrument response was reported by a number of laboratories for the blank feed, all but one laboratory's results were well below the 1 mg/kg limit of quantification. RSDr values for the initial 2 trace-level samples were excessive, ranging from 51.6 to 64.4%. RSDR values ranged from 51.6 to 75.7%, and HorRat values ranged from 3.6 to 4.0. Data for the initial trace-level samples indicated that the test samples were improperly prepared to ensure homogeneity, and a new set of supplemental samples was provided to collaborators, with significantly improved results. RSDr values for the 2 supplemental trace-level samples ranged from 1.6 to 2.5%, RSDR values ranged from 5.6 to 9.2%, and HorRat values ranged from 0.43 to 0.62.