Spatial, Ecologic, and Clinical Epidemiology of Community-onset, Ceftriaxone-resistant Enterobacteriaceae, Cook County, Illinois, USA

Vanessa Sardá; William E. Trick; Huiyuan Zhang; David N. Schwartz

Disclosures

Emerging Infectious Diseases. 2021;27(8):2127-2134. 

In This Article

Results

We collected 12,892 Enterobacteriaceae isolates at CCH during the study period, 10,891 of which met the inclusion criteria and were included in the dataset. We summarized the demographic and clinical characteristics of the patients from whom Enterobacteriaceae isolates were collected (Table 1). Most isolates were collected from women (7,853 [72.1%]), were from urine specimens (9,315 [85.5%]), were collected in ambulatory clinics (5,889 [54.1%]), or were identified as E. coli (7,977 [73.2%]). A total of 1,035 (9.5%) Enterobacteriaceae (817 [10.2%] E. coli isolates) were resistant to ceftriaxone. We observed no notable trends in ceftriaxone resistance across study years.

In the 1,319 land census tracts in Cook County, we collected Enterobacteriaceae isolates from residents of 1,131 (85.8%) and E. coli alone from residents of 1,085 (82.3%). The mean number of such isolates per census tract was 9.6 (SD + 9.28, range 1–92), and the mean number of E. coli isolates obtained per census tract was 7.4 (SD + 7.16, range 1–62). We plotted choropleth maps depicting the geographic distribution of all Enterobacteriaceae isolates and E. coli isolates alone (Figure 1). Among census tracts from which >1 isolate was obtained, CTX-R Enterobacteriaceae isolates were identified in 500 (44.2%), and most CTX-R isolates (561 [54.2%]) came from only 125 (11%) census tracts. In the case of CTX-R E. coli isolates, 424 (39.1%) of the 1,085 census tracts had a CTX-R E. coli isolate reported during the study period, and only 93 (8.6%) census tracts accounted for 406 (49.7%) of all CTX-R E. coli isolates.

Figure 1.

Number of Enterobacteriaceae (A) and Escherichia coli (B) isolates collected from patients in the Cook County Health healthcare system, by Cook County census tract, Illinois, USA, 2016–2018.

A total of 886 census tracts had >3 Enterobacteriaceae isolates collected during the study period and were included in the spatial and ecologic analyses. The mean CTX-R percentage among these census tracts was 8.7%. Autocorrelation analysis (Moran I) indicated that CTX-R percentages among all isolates were not distributed randomly across Cook County census tracts (index 0.02, p<0.01). A total of 776 census tracts had >3 E. coli isolates collected during the study period and were included in the spatial and ecologic analysis of E. coli isolates. The average CTX-R percentage of E. coli isolates among census tracts was 9.6%. Autocorrelation analysis (Moran I) of CTX-R percentages among E. coli isolates also found a nonrandom distribution among census tracts (index 0.03, p<0.01). We mapped the geographic distribution of CTX-R percentages for all Enterobacteriaceae and for E. coli isolates alone (Figure 2).

Figure 2.

Percentage of ceftriaxone-resistant Enterobacteriaceae (A) and Escherichia coli (B) isolates collected from patients in the Cook County Health healthcare system, by Cook County census tract, Illinois, USA, 2016–2018.

We identified census tract–level characteristics reported in the 2017 American Community Survey of residents of the 886 census tracts that accounted for >3 Enterobacteriaceae isolates and compared census tracts with ceftriaxone resistance (461 [52.1%] of census tracts, mean 15.5 isolates/census tract) and without (425 [47.9%] of census tracts, mean 8.03 isolates/census tract). Bivariate analysis found that the presence of CTX-R isolates was negatively associated with census-tract percentages of non-Hispanic White and non-Hispanic Black populations, and positively associated with census-tract percentages of Hispanic, foreign-born, and uninsured residents. We observed no statistical associations between the outcome and percentages of households with incomes below the federal poverty level or with overcrowding (Table 2). Census tract-level characteristics were moderately correlated (r = −0.78 to 0.69).

Among the 776 census tracts with >3 E. coli isolates, 395 (50.9%) had no CTX-R isolates and 381 (49.1%) had >1 resistant E. coli isolate collected during the study period, with an average CTX-R percentage of 19.4%. Bivariate analysis showed a negative association between presence of CTX-R E. coli isolates in census tracts and percentage of non-Hispanic Black population. Conversely, the odds of ceftriaxone resistance in an E.coli isolates was positively associated with the percentage of Hispanic, foreign-born, and uninsured residents and with residential overcrowding (Table 3).

All 10,891 Enterobacteriaceae isolates (1,035 [9.5%] of which were CTX-R) were included in the individual risk analysis of patients from whom CTX-R and CTX-susceptible Enterobacteriaceae were recovered (Table 4). In the bivariate logistic regression analysis, male sex, an age range of 35–85 years, race and ethnicity other than non-Hispanic Black, and inpatient encounter were found to be associated with a higher likelihood of ceftriaxone resistance in a clinical isolate. Similarly, higher odds for the outcome were associated with the percentage of foreign-born residents in the census tract of isolate provenance.

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