Can a simple urinalysis predict the causative agent and the antibiotic sensitivities?

OBJECTIVES: The objective of this study was (1) to determine the reliability of urinalysis (UA) for predicting urinary tract infection (UTI) in febrile children, (2) to determine whether UA findings can predict Escherichia coli versus non-E. coli urinary tract infection, and (3) to determine if empiric antibiotics should be selected based on E. coli versus non-E. coli infection predictions.

METHODS: This was a retrospective chart review of children from 2 months to 2 years of age who presented to the emergency department with fever (rectal temperature >100.4°F) and had a positive urine culture. This study was conducted between January 2004 and December 2007. Negative UA was defined as urine white blood cell count less than 5 per high-power field, negative leukocyte esterase, and negative nitrites. Urine cultures were classified into E. coli and non-E. coli groups. These groups were compared for sex, race, and UA findings. Multivariate forward logistic regression, using the Wald test, was performed to calculate the likelihood ratio (LR) of each variable (eg, sex, race, UA parameters) in predicting UTI. In addition, antibiotic sensitivities between both groups were compared.

RESULTS: Of 749 medical records reviewed, 608 were included; negative UA(-) was present in 183 cases, and positive UA(+) was observed in 425 cases. Furthermore, 424 cases were caused by E. coli, and 184 were due to non-E. coli organisms. Among 425 UA(+) cases, E. coli was identified in 349 (82.1%), whereas non-E. coli organisms were present in 76 (17.9%); in contrast, in 183 UA(-) cases, 108 (59%) were due to non-E. coli organisms versus 75 (41%), which were caused by E. coli. Urinalysis results were shown to be associated with organism group (P < 0.001). Positive leukocytes esterase had an LR of 2.5 (95% confidence interval [CI], 1.5-4.2), positive nitrites had an LR of 2.8 (95% CI, 1.4-5.5), and urine white blood cell count had an LR of 1.8 (95% CI, 1.3-2.4) in predicting E. coli versus non-E. coli infections. Antibiotic sensitivity compared between UA groups demonstrated equivalent superiority of cefazolin (94.7% sensitive in UA(+) vs 84.0% in UA(-) group; P < 0.0001), cefuroxime (98.2% vs 91.7%; P < 0.001), and nitrofurantoin (96.1% vs 82.2%; P < 0.0001) in the UA(+) group. In contrast, the UA(-) group showed significant sensitivity to trimethoprim-sulfamethoxazole (82.2% vs 71.3% in UA(+); P = 0.008).

CONCLUSIONS: Urinalysis is not an accurate predictor of UTI. A positive urine culture in the presence of negative UA most likely grew non-E. coli organisms, whereas most UA(+) results were associated with E. coli. This study also highlighted local patterns of antibiotic resistance between E. coli and non-E. coli groups. Negative UA results in the presence of strong suspicion of a UTI suggest a non-E. coli organism, which may be best treated with trimethoprim-sulfamethoxazole. Conversely, UA(+) results suggest E. coli, which calls for treatment with cefazolin or cefuroxime.