Infections of the urinary tract are the most common of all bacterial infections, and cause significant morbidity worldwide. The urinary system consists of the kidneys, ureters, prostate (in men), bladder, and urethra. On a daily basis, there is large variability in the amount and type of food and fluids that are consumed. The kidneys play a large role in maintaining fluid and electrolyte balance. Urine is produced by the kidneys as a result of filtration of the blood that passes through the kidneys. This urine travels through the ureter to the bladder, and together, the kidneys and bladder are considered the upper urinary tract.
Infection of the kidneys and prostate are termed pyelonephritis and prostatitis, respectively. The lower urinary tract consists of the bladder as well as the urethra, which is the organ that allows for excretion of urine from the bladder to outside of the body.
Infection of the bladder and urethra are termed cystitis and urethritis, respectively. Both the upper and the lower urinary tracts can be infected with a variety of organisms, producing different symptoms and consequences, and requiring different treatments.
Urinary tract infections (UTIs) are frequently defined by detection of pathogenic microorganisms in the urine, urethra, bladder, kidney, or prostate. When a sample of urine is appropriately collected and cultured, the growth of more than 105 organisms from 1 milliliter of urine is considered an infection. However, if a patient is experiencing symptoms of an UTI, then there is often a lower threshold to the number of bacteria that need to be present to diagnose and infection. Bacteria can enter the urinary system from direct entry through the urethra, or they can be introduced as a consequence of catheter insertion or a surgical procedure.
Infections of the urinary tract are more common in women than in men, except when individuals are very young or old. Up to 80 percent of women will experience a UTI, most often cystitis, at some point in their lives. This high number is thought to be due to the shorter urethra (4 centimeters) in women as compared to men. Approximately one-quarter of women who have had one UTI will have a recurrent infection. Women are also at increased risk of pyelonephritis. Factors associated with pyelonephritis in women include frequency of sexual intercourse, a new sexual partner, UTI in the past year, history of UTI in the patient’s mother, diabetes, and incontinence. Women with diabetes also have an increased risk of UTIs.
The incidence of UTIs in women is further increased during pregnancy. Up to 10 percent of pregnant women are found to have bacteria in their urine although they are asymptomatic. If not treated, up to 40 percent of these women will develop pyelonephritis, which increases the rate of premature deliveries and perinatal death.
During infancy, males have a higher prevalence of congenital anomalies that predispose them to UTIs, and thus have a higher incidence of UTIs than females. In addition, after 50 years of age, the incidence of UTIs is similar between men and women, largely because older men often have enlarging prostates, potentially causing urinary obstruction and increased risk for infection. There does not seem to be an increase in UTIs in men with diabetes as there is in women. During the intervening years, infections of the urinary tract in males are rare, and often acquired via sexual contact.
There are a large number of bacteria that can potentially cause infection of different parts of the urinary tract. For young women with cystitis, the majority of infections are caused by Escherichia coli, followed by Staphylococcus saprophyticus, Klebsiella species, Proteus species, and enterococcus species. It is most often the case that bacteria enter the urinary tract via ascent through the urethra into the bladder, and then retrograde through the ureters to the kidney. The normal bacterial flora around the urethra consists of diphtheroids, streptococcal species, lactobacilli, and staphylococcal species that are not associated with UTIs. The bacteria that cause UTIs colonize the area around the urethra and the opening of the vagina and are thought to come from the bowel.
The entry of bacteria into the bladder does not always cause infection, and the body has a number of ways to eliminate invading bacteria. Normal urination often flushes the organisms from the bladder and urethra. In addition, the mucosal surface of the bladder has antibacterial properties, and the urine creates an environment that is inhospitable to bacteria with a low pH, a high concentration of urea and organic acids, and a high concentration of solutes.
However, there are predisposing factors that can override these defenses and lead to infection, including alterations in the normal vaginal flora by antibiotic treatment, genital infections, the use of contraceptives such as spermicides, and increased rate of entry secondary to urethral massage during vaginal intercourse.
UTIs can be classified as symptomatic or asymptomatic. Asymptomatic bacteruria is when bacteria can be detected in the urine but the person experiences no symptoms. When a patient experiences symptoms of cystitis, they often report pain or burning with urination, the sensation of needing to urinate frequently, an urge to urinate, and pain the lower abdomen. Often, the urine itself looks cloudy or contains blood and can be malodorous. These symptoms are not life threatening but cause significant discomfort and, if untreated, can lead to infections of the upper urinary tract. If the patient has a fever, nausea and vomiting, diarrhea, as well as tenderness in the flanks (overlying the kidneys), these are often symptoms of an upper UTI, such as pyelonephritis.
The location of the UTI has a large influence on the type, length and success of treatment. If the infection is restricted to the bladder, often a single antimicrobial agent to which the bacteria is susceptible can be used to rapidly treat the infection. It is recommended that after treatment, a test of cure is performed to ensure that bacteria are no longer found in the urine. This is becoming especially important as an increasing number of bacteria are becoming resistant to common antibiotics. If it is a case of complicated cystitis, secondary to catheterization, an anatomic abnormality, or obstruction, the infecting bacteria is often resistant to antibiotics and drug therapy must have wide coverage.
Pregnant women should be routinely screened during the first trimester for asymptomatic UTIs and treated. When the infection includes the upper urinary tract, treatment courses of several weeks may be necessary, and may be initiated using intravenous antibiotics during a hospital stay. Most cases of UTIs, including cystitis and pyelonephritis, resolve without further complications.
Antibiotics; Bacterial Infections; E. Coli Infections; Pregnancy; Prenatal Care; Women’s Health Care (General).
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