Background There is little evidence on the ecological effect and sustainability of antimicrobial stewardship programmes (ASPs) in primary-care settings. We aimed to determine whether a multimodal, educational ASP would be sustainable in the long-term and reduce the incidence of infections caused by extended-spectrum beta-lactamase-producing Escherichia coli in the community by optimising antibiotic use. Methods We did this quasi-experimental intervention study in 214 primary health centres of four primary health-care districts in Andalusia, Spain. Local multidisciplinary teams, comprised of general practitioners, paediatricians, primary-care pharmacists, and epidemiologists, were created in each district and implemented a multimodal, education-based ASP. The core activity of the programme consisted of regular one-to-one educational interviews between a reference interviewing physician and prescribing physicians from each centre on the appropriateness of their most recent (same or preceding day) antibiotic prescriptions based on a structured questionnaire. Appropriate prescribing was defined as compliance of all checklist items with the reference guidelines. An average of five educational interviews were scheduled per prescriber per study year. We did an interrupted time-series analysis to assess the effect of the intervention on quarterly antibiotic use (prescription and collection by the patient) and quality of prescriptions (as defined daily doses per 1000 inhabitants per day) and incidence per 1000 inhabitants of E coli producing extended-spectrum beta-lactamase (ES BL) isolated from urine samples. Findings The study was done between January, 2012, and December, 2017, in a pre-intervention period of 2012-13 and an intervention period of 2014-17. Throughout the study period, there were 1387 physicians (1116 general practitioners and 271 paediatricians) in the included health centres serving a mean population of 1937512 people (299 331 children and 1638181 adults). 24 150 educational interviews were done over the 4 years. Inappropriate antibiotic prescribing was identified in 1794 (36.5%) of 4917 educational interviews in 2014 compared with 1793 (26.9%) of 6665 in 2017 (p<0.0001). The intervention was associated with a sustained reduction in the use of ciprofloxacin (relative effect -15 - 9%, 95% CI -23.9 to -8.0) and cephalosporins (-22.6%, -35.9 to -9.2), and a sustained increase in the use of amoxicillin (22.2%, 6.4 to 3 8. 0) and fosfomycin trometamol (6.1%, 2.6 to 9 - 6). The incidence density of ES BL-producing E coli decreased by -0.028 cases per 1000 inhabitants (95% CI -0.034 to -0 -0 21) after the start of the programme, reversing the pre-intervention increase and leading to a relative reduction of -65.6% (-68 - 2 to -63.0) 4 years later. Interpretation Our data suggest that implementation of a multimodal ASP in primary care that is based on individual educational interviews improves the use of antibiotics and results in a sustained significant reduction of infections by ES BL-producing E coli in the community. This information should encourage the implementation of ASPs in primary care. Copyright (C) 2019 Elsevier Ltd. All rights reserved.