Complicated UTI

Presentation and Causes of a UTI

Urinary tract infections (UTIs) are categorized as uncomplicated or complicated.1 Uncomplicated UTIs typically occur in females because they have a shorter urethra than males, which is more likely to become colonized by bacteria. With an uncomplicated UTI, there are no structural abnormalities and no comorbidities.2 Uncomplicated UTIs can typically be treated on an outpatient basis with a course of antibiotics.1 Many cases of uncomplicated UTIs may also resolve spontaneously without treatment.1, 2

Complicated UTIs are those that carry a higher risk of treatment failure and typically require longer antibiotic courses.1 Infection typically occurs due to colonization with perineal flora, most commonly, Escherichia coli.1 Other causative organisms are proteus, klebsiella, and enterococcus.2

Complicated UTIs have a broad range of etiologies. UTIs are classified as complicated:

  • When they occur in:
    • Males
    • Pregnant females
    • Renal transplant patients
    • Immunocompromised patients
    • Older adults
    • Patients with impaired renal function
  • As a result of:
    • Obstruction
    • Hydronephrosis
    • Renal tract calculi
    • Colovesical fistula
  • Due to:
    • Atypical organisms
    • Instrumentation or in conjunction with medical equipment, such as urinary catheters
    • Prostatectomy
    • Radiotherapy1

Clinical symptoms consistent with an uncomplicated UTI include increased urinary frequency and urgency, hematuria, dysuria, and suprapubic pain.1 A Complicated UTI shares these symptoms but patients can present with additional features depending on the specific etiology.

With kidney involvement, symptoms such as fever, chills, nausea, vomiting, or back pain are more likely to occur.2 Severe complicated UTIs may also present as sepsis or septic shock.1 Older adults may present with atypical symptoms such as delirium.1

Distinguishing between uncomplicated and complicated UTIs is important because treatment approaches differ based on the classification.1

Diagnostic Workup/Differential Diagnosis

A high quality, mid-stream urine sample or catheterized urine sample may be used as a part of the diagnostic criteria.1 Urinalysis typically reveals positive leukocyte esterase.3 Other helpful urinalysis values are pH, nitrites, and blood.2

A negative urinalysis does not rule out UTI so a urine culture should be performed.2 Performing a urine culture is especially important to confirm susceptibility of the urinary bacteria to the antibiotic prescribed.2 A quantitative count of at least 108 cfu/L in a voided specimen indicates infection, while a quantitative count of at least 105 cfu/L in a urine specimen obtained via catheter is consistent with infection.3

A blood culture must be performed if the presentation is consistent with sepsis.1 All patients who present with a complicated UTI may also undergo imaging via ultrasound or CT to investigate for anatomical abnormalities.1

The differential diagnosis includes acute pyelonephritis, bladder cancer, chlamydial genitourinary infections, cystitis, herpes simplex, interstitial cystitis, pelvic inflammatory disease, prostatitis, urethritis, and vaginitis.1

Management of a Complicated UTI

For patients presenting with sepsis, treatment may require extensive fluid resuscitation and parenteral broad spectrum antibiotics.1 Nonseptic patients are typically treated in outpatient settings with oral antibiotics.1

Patients typically receive a broad spectrum antibiotic while awaiting results of urine culture, after which they ideally receive a narrow spectrum antibiotic tailored to the specific etiologic organism.1 Examples of broad spectrum antibiotics used for the treatment of complicated UTIs include penicillins or beta-lactams, cephalosporins, fluoroquinolones, and carbapenems.1 Treatment response is indicated by improved clinical symptoms and should occur within 48 to 72 hours.1 The typical treatment duration for a complicated UTI is 10 to 14 days.1

Antibiotics that are typically used as the first line of treatment for uncomplicated UTIs — such as nitrofurantoin, sulfamethoxazole-trimethoprim (SMX-TMP), and fosfomycin — may not typically be used in complicated UTIs due to the increased risk of resistant etiologic organisms associated with complicated UTIs.4


Common adverse effects may include nausea, vomiting, diarrhea, rash, abdominal pain, and urticaria.5 Drug-drug interactions may occur with sulfonamides, erythromycin, chloramphenicol, probenecid, and others.5 Contraindications include severe allergic reaction to penicillin and Clostridium difficile-associated diarrhea, among others.5

Therapeutic drug monitoring is not typically required but monitoring of adverse effects should occur.5 An example of a medication in this class that may be used for the treatment of a complicated UTI is amoxicillin-clavulanate.


Like penicillins, carbapenems are within the beta-lactam class of antibiotics but have a broader spectrum of action against beta-lactamases.6


There are five generations of these antibiotics grouped by spectrum of coverage.7 First generation cephalosporins such as cephalexin have coverage against E. coli.7 Common adverse effects of cephalosporins include nausea, vomiting, lack of appetite, and abdominal pain.7 More severe adverse effects such as anaphylaxis, hemolytic anemia, and pseudomembranous colitis may also occur.7

Drug-drug interactions may occur including increased nephrotoxicity with co-administration of aminoglycosides.7 Contraindications include severe allergic reactions to cephalosporins or penicillins.7 Monitoring for adverse effects should occur.7


The use of these broad spectrum antibiotics is typically more restricted due to the potential for severe side effects.8 Due to chelation, oral absorption is reduced when these medications are taken with other medications that contain metallic ions such as multivitamins or antacids.8 Common adverse effects of fluoroquinolones include nausea, vomiting, diarrhea, arthralgias, and skin reactions such as photosensitivity.8 More serious adverse effects include tendinopathies and tendon rupture, QTc prolongation, and aortic aneurysm, among others.8

Additionally, central nervous system-related effects of fluoroquinolones, such as confusion and weakness, may occur and are especially important to consider within the context of treating older adult patients.8 Fluoroquinolones are contraindicated and should not be used for children or pregnant patients.8 Monitoring of adverse effects should occur.8 Examples of medications in this class that may be used for the treatment of complicated UTIs include ciprofloxacin, norfloxacin, and levofloxacin.4

UTI Complications

UTIs may be associated with severe complications such as sepsis and death.3 Uncommon suppurative complications include paraurethral abscesses, renal or perirenal abscess, and metastatic infection including bone and joint infection or endocarditis.3

Complicated UTI Monitoring

Monitoring for clinical improvement of complicated UTI symptoms 48 to 72 hours after antibiotic initiation is important.3 Patients who do not respond to initial treatment should be reevaluated to rule out urinary obstruction, abscess, an antibiotic-resistant infection, or other alternate diagnoses.3 Similarly, patients who have a recurrence of symptoms within a few weeks require further evaluation.4


  1. Sabih A, Leslie S. Complicated Urinary Tract Infections. In: StatPearls. NCBI Bookshelf version. StatPearls Publishing: 2021. Accessed July 27, 2022.
  2. Bono M, Reygaert W. Urinary Tract Infection. In: StatPearls. NCBI Bookshelf version. StatPearls Publishing: 2021. Accessed July 27, 2022.
  3. Nicolle L. Complicated urinary tract infection in adults. Can J Infect Dis Med Microbiol. 2005;16(6):349-360. doi:10.1155/2005/385768
  4. Li R, Leslie S. Cystitis. In: StatPearls. NCBI Bookshelf version. StatPearls Publishing: 2022. Accessed July 27, 2022.
  5. Yip D, Gerriets V. Penicillin. In: StatPearls. NCBI Bookshelf version. StatPearls Publishing: 2022. Accessed July 27, 2022.
  6. Pandey N, Cascella M. Beta Lactam Antibiotics. In: StatPearls. NCBI Bookshelf version. StatPearls Publishing: 2022. Accessed July 27, 2022.
  7. Bui T, Preuss C. Cephalosporins. In: StatPearls. NCBI Bookshelf version. StatPearls Publishing: 2022. Accessed July 27, 2022.
  8. Yan A, Bryant E. Quinolones. In: StatPearls. NCBI Bookshelf version. StatPearls Publishing: 2021. Accessed July 27, 2022.

Author Bio

Anna Courant is a nurse practitioner and writer.