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Key Points Question How is the instantaneous reproduction number of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) associated with social distancing, wet-bulb temperature, and population density in counties across the United States? Findings In this cohort study of 211 counties in 46 states, social distancing, temperate weather, and lower population density were associated with a decrease in the instantaneous reproduction number of SARS-CoV-2. Of these county-specific factors, social distancing appeared to have the most substantial association with a reduction in SARS-CoV-2 transmission. Meaning In this study, the instantaneous reproduction number of SARS-CoV-2 varied substantially among counties; the associations between the reproduction number and county-specific factors could inform policies to reduce SARS-CoV-2 transmission in selective and heterogeneous communities., This cohort study examines the association of county-level factors with variation in the instantaneous reproduction number of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the United States., Importance Local variation in the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) across the United States has not been well studied. Objective To examine the association of county-level factors with variation in the SARS-CoV-2 reproduction number over time. Design, Setting, and Participants This cohort study included 211 counties, representing state capitals and cities with at least 100 000 residents and including 178 892 208 US residents, in 46 states and the District of Columbia between February 25, 2020, and April 23, 2020. Exposures Social distancing, measured by percentage change in visits to nonessential businesses; population density; and daily wet-bulb temperatures. Main Outcomes and Measures Instantaneous reproduction number (Rt), or cases generated by each incident case at a given time, estimated from daily case incidence data. Results The 211 counties contained 178 892 208 of 326 289 971 US residents (54.8%). Median (interquartile range) population density was 1022.7 (471.2-1846.0) people per square mile. The mean (SD) peak reduction in visits to nonessential business between April 6 and April 19, as the country was sheltering in place, was 68.7% (7.9%). Median (interquartile range) daily wet-bulb temperatures were 7.5 (3.8-12.8) °C. Median (interquartile range) case incidence and fatality rates per 100 000 people were approximately 10 times higher for the top decile of densely populated counties (1185.2 [313.2-1891.2] cases; 43.7 [10.4-106.7] deaths) than for counties in the lowest density quartile (121.4 [87.8-175.4] cases; 4.2 [1.9-8.0] deaths). Mean (SD) Rt in the first 2 weeks was 5.7 (2.5) in the top decile compared with 3.1 (1.2) in the lowest quartile. In multivariable analysis, a 50% decrease in visits to nonessential businesses was associated with a 45% decrease in Rt (95% CI, 43%-49%). From a relative Rt at 0 °C of 2.13 (95% CI, 1.89-2.40), relative Rt decreased to a minimum as temperatures warmed to 11 °C, increased between 11 and 20 °C (1.61; 95% CI, 1.42-1.84) and then declined again at temperatures greater than 20 °C. With a 70% reduction in visits to nonessential business, 202 counties (95.7%) were estimated to fall below a threshold Rt of 1.0, including 17 of 21 counties (81.0%) in the top density decile and 52 of 53 counties (98.1%) in the lowest density quartile.2 Conclusions and Relevance In this cohort study, social distancing, lower population density, and temperate weather were associated with a decreased Rt for SARS-CoV-2 in counties across the United States. These associations could inform selective public policy planning in communities during the coronavirus disease 2019 pandemic.

Importance Escherichia coliis a leading cause of serious infection among term and preterm newborn infants. Surveillance of antibiotic susceptibility patterns ofE coliamong infants admitted to neonatal intensive care units should inform empirical antibiotic administration. Objective To assess the epidemiologic characteristics and antibiotic susceptibility patterns ofE coliin infants admitted to neonatal intensive care units in the US over time. Design, Setting, and Participants This retrospective cohort study used the Premier Health Database, a comprehensive administrative database of inpatient encounters from academic and community hospitals across the US. Participants included newborn infants admitted to centers contributing microbiology data from January 1, 2009, to December 31, 2017, withE coliisolated from blood, cerebrospinal fluid, or urine cultures. Data were collected and analyzed from December 1, 2018, to November 30, 2019. Main Outcomes and Measures Changes in annual antibiotic susceptibility ofE coliduring the study period. The proportion of infants with nonsusceptible organisms (resistant or intermediate susceptibility) in antibiotic categories by year, birth weight, infection source, and timing of infection and patient and center characteristics associated with neonatalE coliinfection and antibiotic susceptibility were assessed. Results A total of 721 infants (434 male [60.2%]; median age atE coliinfection, 14 days [interquartile range, 1-33 days]) from 69 centers had at least 1 episode ofE coliinfection and available susceptibility results. No significant changes were observed over time in the overall annual proportions of antibiotic nonsusceptibility to ampicillin (mean [SD], 66.8% [1.5%]; range, 63.3% to 68.6%; estimated yearly change, −0.28% [95% CI, −1.75% to 1.18%]), nonsusceptibility to aminoglycosides (mean [SD], 16.8% [4.5%]; range, 10.7% to 23.2%; estimated yearly change, −0.85% [95% CI, −1.93% to 0.23%]), or extended-spectrum β-lactamase phenotype (mean [SD], 5.0% [3.7%]; range, 0% to 11.1%; estimated yearly change, 0.46% [95% CI, −0.18% to 1.11%]). No isolates with nonsusceptibility to carbapenems were identified. Among 218 infants with early-onset infection, 22 (10.1%) had isolates with nonsusceptibility to both ampicillin and gentamicin, the antibiotics most commonly administered to newborns as empirical therapy. Conclusions and Relevance In this cohort study, nonsusceptibility to commonly administered antibiotics was found in substantial proportions of neonatalE coliisolates, with no significant change from 2009 to 2017. These findings may inform empirical antibiotic choices for newborn infants.