• Johnathan M Sheele, Claudia R Libertin, Isaac Fink, Taylor Jensen, Nicole Dasalla, and Timothy D Lyon.
• Department of Emergency Medicine, Mayo Clinic, Jacksonville, Florida.
• J Emerg Med. 2022 Mar 1; 62 (3): 368-377.

BackgroundThe Proteeae group (i.e., Proteus species, Morganella morganii, and Providencia species) frequently causes urinary tract infections (UTIs) and is generally resistant to nitrofurantoin. Proteeae species can produce urease, which can increase urine pH.ObjectiveOur aim was to determine whether higher urine pH in the emergency department is associated with nitrofurantoin resistance.MethodsA single health system database of emergency department patients aged 18 years and older who received urinalysis between April 18, 2014, and March 7, 2017, was examined using χ2 test and multivariable regression analysis.ResultsOf 67,271 urine samples analyzed, 13,456 samples grew a single bacterial species. Urine cultures growing the Proteeae group were associated with significantly more alkaline urine than other bacteriuria cultures (odds ratio [OR] 2.20, 95% confidence interval [CI] 2.06-2.36; p < 0.001). The Proteeae species represented 4.4% of urine samples at pH 5-7, 24.4% at pH 8-9, and 40.0% at pH 9. At urine pH 5-7, 80.4% of urine samples were sensitive to nitrofurantoin; however, this percentage decreased to 66.1% for urine pH 8-9 and 54.6% for urine pH 9. Nitrofurantoin had the highest OR (2.10, 95% CI 1.85-2.39) among cefazolin, ciprofloxacin, and trimethoprim/sulfamethoxazole for bacteriuria sensitive to those antibiotics at urine pH 5-7. At urine pH 8-9 and 9, nitrofurantoin had the lowest OR among the antibiotics: 0.48 (95% CI 0.42-0.54) and 0.31 (95% CI 0.24-0.40), respectively (p < 0.001 for both).ConclusionsUrine pH of 8 or higher is associated with high rates of nitrofurantoin resistance.Copyright © 2021 Elsevier Ltd. All rights reserved.

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