RESUMEN
BACKGROUND: In 2016, a study in a Dutch nursing home showed prolonged colonization duration of extended-spectrum ß-lactamase-producing (ESBL)-ST131 compared to ESBL-non-ST131. In this study, we assessed the duration of rectal ESBL-producing E. coli (ESBL-EC) colonization in residents in the same nursing home for an extended period of six years. We aimed to estimate the influence of a possible bias when follow up is started during an outbreak. METHODS: Between 2013 and 2019, repetitive point prevalence surveys were performed by culturing rectal or faecal swabs from all residents. Kaplan-Meier survival analysis was performed to calculate the median time to clearance of ESBL-EC with a log-rank analysis to test for differences between ESBL-ST131 and ESBL-non-ST131. RESULTS: The study showed a median time to clearance of 13.0 months (95% CI 0.0-27.9) for ESBL-ST131 compared to 11.2 months (95% CI 4.8-17.6) for ESBL-non-ST131 (p = 0.044). In the subgroup analysis of residents who were ESBL-EC positive in their first survey, the median time to clearance for ST131 was 59.7 months (95% CI 23.7-95.6) compared to 16.2 months (95% CI 2.1-30.4) for ESBL-non-ST131 (p = 0.036). In the subgroup analysis of residents who acquired ESBL-EC, the median time to clearance for ST131 was 7.2 months (95% CI 2.1-12.2) compared to 7.9 months (95% CI 0.0-18.3) for ESBL-non-ST131 (p = 0.718). The median time to clearance in the ESBL-ST131 group was significantly longer in residents who were ESBL-ST131 colonised upon entering the study than in residents who acquired ESBL-ST131 during the study (p = 0.001). CONCLUSION: A prolonged colonization with ESBL-ST131 was only found in the subgroup who was ESBL-EC positive upon entering the study. The prolonged duration with ESBL-ST131 in the previous study was probably biased by factors that occured during (the start of) the outbreak.