Nitrofurantoin resistance as an indicator for multidrug resistance: an assessment of Escherichia coli urinary tract specimens in England, 2015–19

Objectives
To determine whether MDR occurs more frequently in nitrofurantoin-resistant Escherichia coli urinary isolates in England, compared with nitrofurantoin-susceptible isolates.

Methods
Using routine E. coli urine isolate antibiotic susceptibility laboratory surveillance data for England, 2015–19 inclusive, the percentage of MDR or XDR phenotype was estimated for nitrofurantoin-susceptible and nitrofurantoin-resistant laboratory-reported urinary tract samples by region, patient sex and age group.

Results
Resistance to nitrofurantoin among E. coli urinary samples decreased slightly year on year from 2.9% in 2015 to 2.3% in 2019. Among E. coli UTIs tested for nitrofurantoin susceptibility and  ≥3 additional antibiotics, the percentage that were MDR was consistently 15%–20% percentage points higher for nitrofurantoin-resistant isolates compared with nitrofurantoin-susceptible isolates. Similarly, the percentage of isolates with an XDR phenotype was higher among nitrofurantoin-resistant versus -susceptible isolates (8.7% versus 1.4%, respectively, in 2019); this disparity was greater in male patients, although variation was seen by age group in both sexes. Regional variation was also noted, with the highest MDR percentage amongst nitrofurantoin-resistant E. coli urinary samples in the London region (36.7% in 2019); the lowest was in the North East (2019: 16.9%).

Conclusions
MDR and XDR phenotypes occur more frequently in nitrofurantoin-resistant E. coli urinary isolates in England, compared with nitrofurantoin-susceptible isolates. However, nitrofurantoin resistance is low (<3%) overall. This latest study provides important insights into trends in nitrofurantoin resistance and MDR, which is of particular concern for patients ≥75 years old and those who are male. It also emphasises geographical heterogeneities within England in nitrofurantoin resistance and MDR.