The Institutional Review Board of the University of California San Diego approved this retrospective cohort study. We searched the electronic medical record for urine cultures obtained at the Rady Children's Hospital ED or urgent care centers from January 1, 2013, to December 31, 2018. We defined UTIs as a urine culture yielding \(\ge\) 50,000 CFU/mL of a single urinary pathogen obtained by catheterization or a urine culture yielding \(\ge\)100,000 CFU/mL obtained by clean catch. Patients diagnosed with a UTI during hospitalization were excluded to capture only community acquired UTIs. Urine cultures with mixed bacterial growth or normal flora were excluded.
Antimicrobial susceptibilities were determined according to the Clinical and Laboratory Institute (CLSI) guidelines in which ESBL organisms are identified by an increase ≥ 5 mm in the zone of inhibition in the presence of clavulanic acid added to a ceftazidime disc.15
For patients with confirmed uropathogens on culture, we extracted the home street address from the medical record. We excluded addresses outside of San Diego County, post office box addresses, and those with reported confidential addresses. We mapped the patient addresses and aggregated locations to census tracts to protect privacy.
The California Environmental Protection Agency published the California Communities Environmental Health Screening Tool, referred to as CalEnviroScreen v.3.0, which serves to identify California communities by census tract that are disproportionally burdened by multiple sources of pollution (https://oehha.ca.gov). CalEnviroScreen ranks census tracts in California based on potential exposures to pollutants, adverse environmental conditions, socioeconomic factors, and prevalence of certain health conditions. A high score indicates a high pollution burden for the census tract.
The Centers for Disease Control and Prevention (CDC) created the Social Vulnerability Index (SVI) to aid in disaster planning and management (https://www.atsdr.cdc.gov). More recently, it has been used to assess a community’s vulnerability to health-related outcomes.16–18 The SVI contains15 socio-demographic census variables, grouped into four themes: 1) socioeconomic status; 2) household composition and disability; 3) race, ethnicity, and language; and 4) housing type and transportation. Census tract rankings are based on percentiles. Percentile ranking values range from 0 to 100, with higher values indicating greater vulnerability. For each tract, a percentile rank is generated for the four themes and its overall position. More details regarding the variables are available at https://www.atsdr.cdc.gov.
We calculated both crude and adjusted rates of ESBL uropathogens for each census tract in the study area. The primary outcome for this study was the proportion of positive ESBL uropathogens of all the ESBL-capable uropathogens by unit of the census tract.
We performed spatial analysis of the adjusted rates in each census tract to assess nonrandom geographic clusters. We used Anselin-Local Moran’s I statistic to assess whether a census tract is similar (spatial cluster) or dissimilar (spatial outlier) to neighboring tracts and whether the pattern is more than expected in a random distribution.19 This is especially useful in our aim to identify locations where there are unexpectedly high concentration of ESBL uropathogens across the study area. A “high cluster” is a census tract with high rates of ESBL uropathogens surrounded by census tracts with similarly high rates. A “high outlier” is a census tract with high rates of ESBL uropathogens surrounded by census tracts with low rates. A “low cluster” is a census tract with low rates of ESBL uropathogens surrounded by census tracts with similarly low rates. A “low outlier” is a census tract with low rates of ESBL uropathogens surrounded by census tracts with low rates. We used ArcGIS software (ESRI, Redlands, CA) for performing both geocoding and spatial analysis.