From the Guidelines
Urinary tract infections that test positive for nitrites are typically caused by gram-negative bacteria, particularly Enterobacteriaceae like Escherichia coli, Klebsiella, and Proteus species. These bacteria convert nitrates in urine to nitrites, which is what the test detects. The most recent and highest quality study 1 recommends first-line therapy with nitrofurantoin, trimethoprim-sulfamethoxazole (TMP-SMX), or fosfomycin for the treatment of symptomatic UTIs in women. Some key points to consider in the treatment of UTIs include:
- Nitrofurantoin (100mg twice daily for 5-7 days),
- trimethoprim-sulfamethoxazole (160/800mg twice daily for 3 days),
- or fosfomycin (3g single dose) as first-line options. For more complicated infections, fluoroquinolones like ciprofloxacin (250-500mg twice daily for 7-14 days) may be used. While waiting for treatment to begin, drinking plenty of water helps flush bacteria from the urinary tract. Completing the full course of antibiotics is essential even if symptoms improve quickly. The effectiveness of these treatments stems from their ability to either kill the bacteria or prevent their reproduction, allowing the body's immune system to clear the infection. For recurrent UTIs, preventive strategies include urinating after sexual activity, wiping from front to back, staying hydrated, and possibly taking prophylactic antibiotics in some cases 1. It is also important to note that antibiotic prophylaxis should be approached judiciously, considering the risk of antibiotic resistance and adverse effects 1. Overall, the treatment of UTIs should be guided by the most recent and highest quality evidence, with a focus on minimizing morbidity, mortality, and improving quality of life.
From the FDA Drug Label
For the treatment of urinary tract infections due to susceptible strains of the following organisms: Escherichia coli, Klebsiella species, Enterobacter species, Morganella morganii, Proteus mirabilis and Proteus vulgaris Urinary Tract Infections – caused by beta-lactamase–producing isolates of E. coli, Klebsiella species, and Enterobacter species.
The UTIs that create nitrites are typically caused by gram-negative bacteria, such as:
- Escherichia coli (E. coli)
- Klebsiella species
- Enterobacter species These bacteria are capable of reducing nitrate to nitrite, which can be detected in a urine test 2, 3.
From the Research
Causes of UTIs that Test Positive for Nitrites
- UTIs caused by Gram-negative bacteria, such as Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis, can test positive for nitrites 4, 5.
- These bacteria produce enzymes that convert nitrate to nitrite, which can be detected in urine 4.
- The presence of nitrite in urine is often used as an indicator of a UTI caused by Gram-negative bacteria 4, 6.
Treatment of UTIs that Test Positive for Nitrites
- The treatment of UTIs that test positive for nitrites depends on the severity of the infection and the susceptibility of the causative organism to antibiotics 7, 8.
- First-line empiric antibiotic therapy for acute uncomplicated bacterial cystitis in otherwise healthy adult nonpregnant females includes a 5-day course of nitrofurantoin, a 3-g single dose of fosfomycin tromethamine, or a 5-day course of pivmecillinam 7.
- For UTIs caused by ESBL-producing Enterobacteriaceae, treatment options include nitrofurantoin, fosfomycin, pivmecillinam, amoxicillin-clavulanate, finafloxacin, and sitafloxacin 7.
- Parenteral treatment options for UTIs due to ESBL-producing Enterobacteriales include piperacillin-tazobactam, carbapenems, ceftazidime-avibactam, and aminoglycosides 7.
Relationship Between Nitrite Presence and Antibiotic Resistance
- The presence of nitrite in urine may be associated with higher resistance rates to certain antibiotics, such as ceftriaxone, cefuroxime, and doxycycline 4.
- However, the absence of nitrite should not affect routine empiric antibiotic choice for presumptive UTI in young children, as the prevalence of enterococcal UTI is low 6.
- Urine bacteriology should be ordered to guide antibiotic therapy, regardless of the presence or absence of nitrite 4.