Urinary tract infection (UTI) is a bacterial infectious disease located in the urinary tract (including urethra, bladder, ureter or kidney), which refers to the inflammatory response of urothelium to pathogenic microorganisms in the urinary tract. Pyuria is the presence of white blood cells in the urine, indicating an inflammatory reaction, while bacteriuria is the presence of bacteria in the urine.
Anatomically, urinary tract infection can be divided into upper urinary tract infection and lower urinary tract infection. Infections of the lower urinary tract include the bladder (cystitis) and urethra (urethritis); infections of the upper urinary tract involve the renal parenchyma and the renal pelvis system and are called pyelonephritis. Urinary tract infections can be further divided into simple and complex. Simple urinary tract infections, also known as uncomplicated urinary tract infections, occur in young, healthy, anatomically normal, non-pregnant women; while complex urinary tract infections are associated with male anatomy, pregnancy, anatomical abnormalities, urinary tract obstruction, urinary catheters and stents, malignancy, chemotherapy and immunosuppression, and antibiotic failure. Acute cystitis is more common, and in premenopausal women, urinary frequency, urgency, lower abdominal pain, and dysuria are the most common symptoms. In postmenopausal women, the elderly and children, patients may present with urinary discomfort, nocturia, urinary incontinence and so on. Other symptoms such as fever, vomiting, and low back pain that follow bladder irritation suggest progression to pyelonephritis. Acute pyelonephritis may present with urinary tract irritation, and often with chills, fever, low back pain, nausea, and vomiting. As the severity of the infection progresses, the patient may experience dizziness, hypotension, and changes in mental status. The incidence of pyelonephritis is much lower than that of cystitis, but the age and sex distributions are similar, with women at higher risk than men, but these differences decrease with age. In addition, catheter-related UTIs are a major risk factor for hospital-acquired UTIs, accounting for almost one-third of all hospital-acquired infections.
The urinary tract is connected to the outside world through the urethral orifice, so it is vulnerable to microbial invasion. Pathogenic bacteria of urinary tract infection usually colonize the tissue around the urethral orifice and can be detected in urine. Urine is a good medium for bacterial growth, so many bacteria can multiply and grow rapidly in the urinary tract. In the majority of cases, bacteria do not cause infectious diseases in the urinary tract, because the host can quickly eliminate bacteria through urination and innate and adaptive immunomodulation. Among them, E. coli is the most common pathogen of urinary tract infection, accounting for 74.4% of outpatients and 65% of hospital-acquired infections. Studies have shown that antibiotic resistance of uropathogenic E. coli has been on the rise in the past 30 years. In addition to E. coli, bacterial species that cause urinary tract infections include Klebsiella, Pseudomonas aeruginosa, and Proteus among Gram-negative bacteria, and Streptococcus and Staphylococcus saprophyticus among Gram-positive bacteria. Patients with recurrent urinary tract infections, men, urinary tract obstruction, or urinary catheters are more likely to have urinary tract infections caused by non-E. coli.
The goal of
urinary tract infection treatment is to eliminate pathogens in the urine, so antibacterial drugs are the key. There are two important factors in antimicrobial selection: first, the pathogen must be sensitive to the antimicrobial; second, the antimicrobial must be concentrated in the urine to a high enough level to be effective against this pathogen (above the minimum inhibitory concentration MIC). Fortunately, urine levels of many antibiotics are often hundreds of times higher than serum levels, so oral doses of commonly used antibiotics can achieve bacteriostatic levels. Therefore, in simple, uncomplicated cystitis, the serum concentration of antimicrobials is not important. By contrast, it is critical for patients with complications such as bacteremia, fever, or infections involving the kidney or prostate parenchyma. In patients with renal insufficiency, whether acute or chronic, an adjustment of the antimicrobial dose primarily through renal clearance may be required. Patients with end-stage renal failure are not able to effectively concentrate drug concentrations in the urine, so eradication of pathogens in the urine is challenging. Finally, because urinary tract obstruction can affect the concentration of antibiotics in the urine, urinary tract obstruction should be resolved as early as possible. The antimicrobial regimens for uncomplicated and complicated UTIs are shown in the figures above, respectively.
Urinary tract infection
