Self-reported risk factors for having Escherichia coli sequence type 131 or its H30 subclone among US Veterans with a clinical E. coli isolate

Among 469 US military veterans with an Escherichia coli clinical isolate (2012–2013), we explored healthcare and non-healthcare risk factors for having E. coli sequence type 131 and its H30 subclone (ST131-H30). Overall, 66 (14%) isolates were ST131; 51 (77%) of these were ST131-H30. After adjustment for healthcare-associated factors, ST131 remained positively associated with medical lines and nursing home residence. After adjustment for environmental factors, ST131 remained associated with wild animal contact (positive), meat consumption (negative) and pet cat exposure (negative). Thus, ST131 was associated predominantly with healthcare-associated exposures, while non-ST131 E. coli were associated with some environmental exposures.

(O16 and O25b only) [6]. PCR was done using boiled lysates for template DNA, with appropriate positive and negative control strains.

Statistical analysis
Comparisons of proportions were made using χ 2 and Fisher exact tests. Exposures associated significantly with either ST131 or H30 were included in multiple logistic regression models, which were performed separately for clinical and environmental risk factors.
By contrast, among ciprofloxacin-resistant isolates, clinical risk factors did not differ significantly between ST131 (n = 53) and non-ST131 (n = 31) isolates (Table 2). Similarly, among ST131 isolates, the only clinical risk factor that differed H30 from non-H30 isolates was wound source, which was weakly associated with non-H30 isolates ( Table 2).
Multiple logistic regression was used to identify clinical variables independently associated with E. coli ST131. Overall, after adjustment for variables significantly associated with ST131 in the univariable analyses, only medical line used in the past 6 months (adjusted OR 2.14, 95% CI 1.23-3.74) and nursing home residence (adjusted OR 2.92, 95% CI 1.3-6.76) remained significantly associated with ST131. In univariable analyses, no clinical variable was associated with ST131 status among ciprofloxacin-resistant isolates and only one variable (wound source) was associated with H30 status among ST131 isolates ( Table 2) and for these subsets, multiple logistic regression was not performed.
Multiple logistic regression was used to identify environmental variables independently associated with carriage of E. coli ST131. After adjustment for variables associated with ST131 in the univariable analyses, contact with wild animals (adjusted OR 2.49, 95% CI 1.16-5.33) remained positively associated and meat consumption (adjusted OR 0.48, 95% CI 0.28-0.82) and pet cat exposure (adjusted OR 0.37, 95% CI 0.17-0.77) remained negatively associated, with ST131. With wild animal contact in the model, contact with animal feces was no longer associated with ST131 (data not shown). Multiple logistic regression was not performed for subjects with ciprofloxacin-resistant E. coli, all of whom reported contact with wild or companion animals, or for subjects with ST131 since within this subset only one H30-associated variable (out-of-state travel) was identified. All variables included results for between 462 and 469 subjects. a Subjects could report more than one co-morbidity. *P-value corresponds to an overall χ 2 test.

Discussion
Here we assessed self-reported demographics, clinical factors and environmental exposures of veterans with an E. coli clinical isolate as predictors of ST131 status (both overall and for fluoroquinolone-resistant isolates) and, among subjects with an ST131 isolate, of H30 subclone status. This is one of few studies to examine non-healthcare-associated risk factors for having a clinical isolate from the pandemic ST131 lineage and specifically its H30 subclone. Our findings support two main conclusions. First, most of the ST131-associated clinical factors represent traditionally recognised risk factors for having an antimicrobial-resistant infection. However, with stratification by fluoroquinolone resistance status, the ST131-specific associations disappeared. This suggests that these healthcare exposures are not specific to ST131, but are generic markers for infection with antimicrobial-resistant E. coli generally.
Second, a modestly (albeit statistically significantly) greater proportion of subjects with non-ST131 E. coli, as opposed to ST131, reported frequent exposure to certain hypothesised environmental risk factors. Specifically, non-ST131 group members reported more frequent meat consumption, cat ownership, city water usage, recent out-of-state travel and touching animal feces. By contrast, ST131 group members reported more contact with wild animals. This suggests that contact with wild animals, or other variables associated with wild animal exposure, predispose specifically to having ST131, as has been suggested by others [7]. Carriage of the ST131-H30 subclone was associated with wound specimens, while non-H30 carriage was associated with past-month out-of-state travel.
The study has several limitations. First, relatively few subjects reported having several of the candidate risk factors (e.g. travel or farm animal exposure), or had ST131-H30Rx, limiting statistical power for these variables. Second, all subjects were veterans, limiting generalisability and possibly contributing to our not finding the typical associations of ST131 with older age, comorbidities and overall poor health [8][9][10]. Third, the requirement for survey completion may have selected for an uncharacteristically healthy and functional subset of veterans. Fourth, risk factors for E. coli acquisition or carriage may have occurred earlier in life and hence were unmeasured in this study. Additional limitations include the risks of false positives from multiple testing and of misclassification due to poor subject recall.
Specific pandemic lineages clearly contribute disproportionately to extraintestinal E. coli infections, especially if antimicrobialresistant, making their potential reservoirs and modes of transmission important to understand. In this veteran-based study population, ST131 was associated preferentially with healthcare-associated exposures and wild animal contact, whereas non-ST131 E. coli were associated with other environmental exposures.