Infections of the Urinary System

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Infections of the Urinary System

LEARNING OBJECTIVES

After reading this chapter, the student should be able to:

• Identify the parts of the urinary system that are the sites of the most common urinary tract infections (UTI)

• Identify the microorganisms that are the most common causes of UTIs

• Describe typical symptoms of a UTI

• Identify and describe the three most common types of UTIs

• List common risk factors for a UTI

• Identify the patient group with the highest risk for a UTI and give reasons why

• Describe the typical diagnosis process to identify a UTI

• Identify and discuss various methods of treatments for UTIs

• List and discuss prevention factors for UTIs in men, women, children, the elderly, and individuals who are immunocompromised

• Identify some of the major groups of antibiotics specifically used in treating a UTI

WHY YOU NEED TO KNOW

As far back as 3000 bce, the Chinese recognized infections and diseases involving the urinary tract and developed an extensive list of herbal remedies. One of the most comprehensive ancient documents dealing with urinary tract infections and potential cures was the Ebers papyrus written in Egypt at about 1550 bce. This document identified the illness and potential herbal cures but did not offer any attempts to explain the actual causes of these infections. In ancient Greece, Hippocrates (460–375 bce) offered an explanation for urinary tract infections that involved an imbalance in the four humors of the body. He noted the presence of sand in urine that came from the consumption of contaminated water by the individual, which eventually led to the formation of stones, blocking the elimination of urine. This blockage caused the imbalance in the humors and the resultant disease. It was not until the mid-nineteenth century that Pasteur documented that microorganisms were responsible for the contamination of urine associated with urinary tract infections. Treatments at this time primarily involved the use of chemicals that altered the pH of the urinary bladder and the lower urinary tract. The development of antibiotics in the twentieth century resulted in modern regimens for effective treatment of urinary tract infections.

Today, in the United States urinary tract infections (UTIs) account for more than 8 million doctor visits each year. Women are especially prone to these infections; one in five to one half of women will develop one or more UTIs in their lifetime. Although UTIs occur with less frequency in men, they can be very serious.

Research is being conducted to develop a vaccine that can prevent the recurrence of UTIs in patients. Thus far there appear to be data indicating that women and children who experience repeated infections are likely to lack certain immunoglobulins to fight off infections. The vaccine stimulates the immune system to produce antibodies that fight the pathogen (see Chapter 20, The Immune System).

Introduction

The urinary system consists of the kidneys, ureters, urinary bladder, and urethra (Figure 15.1). The kidneys are the central organ of the system and are responsible for filtering wastes from the blood as well as for removing any excess liquid, thus forming urine. The functional units in the kidneys are the nephrons (Figure 15.2) and in addition to their filtering capacity they also keep a stable balance of minerals, salts, and other substances to maintain the homeostasis (the maintenance of a relatively stable environment of the body) of the blood. Furthermore, the kidneys produce erythropoietin, the hormone that aids in the formation of red blood cells. The ureters are narrow tubes that carry the urine from the kidneys to the urinary bladder, which stores the urine for later expulsion from the body. The urine stored in the urinary bladder is emptied through the urethra, whose length varies between male and female. The male urethra is longer than the female and the opening is located on the penis. Normally urine is sterile, free of any microorganisms; however, an infection can occur when infectious organisms, usually bacteria from the gastrointestinal tract, gain access to the opening of the urethra and multiply. The urinary tract is one of the most common sites of bacterial infection, particularly in females.

FIGURE 15.1 Diagram of the human urinary system.
The urinary system consists of the kidneys, ureters, the urinary bladder, and the urethra.

FIGURE 15.2 Nephrons are the functional units of the kidneys.
Each nephron has a glomerulus, a Bowman’s capsule, and a tubular portion that consists of the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule, and a collecting duct.

Urinary Tract Infections (UTIs)

There are a number of organisms that can be responsible for a urinary tract infection (UTI) infection but the most common is Escherichia coli, a gram-negative, facultatively anaerobic rod that can thrive in a relatively wide range of pH. The infection may remain localized in the urethra, but the organisms can also travel up the urethra and infect the urinary bladder. When a urinary bladder infection is not treated, it may spread to the kidneys. In a small number of cases, UTIs have been caused by organisms that originated in oral/gum infections. In these cases the organisms traveled through the bloodstream to the kidneys, where they gave rise to a kidney infection. In healthy individuals the urinary system is designed to prevent urine from backing up from the urinary bladder to the ureters and kidneys, and the flow of urine from the bladder typically helps wash away any microorganisms. The prostate gland in men also produces slightly acidic secretions that tend to slow bacterial growth. These structural and chemical mechanisms, along with the actions of a healthy immune system, are normally effective at preventing UTIs. The type of infection is typically defined by the organ or structure where the infection is located.

Organisms that cause UTIs may be sexually transmitted and the infections usually remain limited to the urethra and the organs of the reproductive system. Not all individuals with a UTI show easily recognizable symptoms, but most cases include the following:

• Urgency to urinate

• Burning/painful sensation when urinating (dysuria)

• Frequency of urination, passing only small amounts each time

• Presence of blood or pus in the urine, or a cloudy, strong-smelling urine

Other symptoms may vary among individuals and depend on the specific type of infection. These symptoms may include the following:

• Uncomfortable pressure above the pubic bone in women

• A fullness of the rectum in men

• Pain in the back or side below the ribs

• Irritability

• Loss of appetite in children

Urinary tract infections are identified by the specific location or organ being affected by the microorganisms. The most common infections are urethritis, cystitis, pyelonephritis, leptospirosis, and glomerulonephritis.

Urethritis

Urethritis is a localized infection usually limited to the urethra. It can be caused by E. coli but also by Chlamydia or Mycoplasma, because the urethra is also associated with organs of the reproductive system. A common source of this infection for older or hospitalized patients is a catheter. If not treated early, the infection can travel up the catheter and spread the infection to the urinary bladder. Trichomonas vaginalis, a protozoan, has also been associated with urethritis as well as vaginitis (see Chapter 16, Infections of the Reproductive System). Enterococci and Candida albicans are other organisms that occasionally can cause urethritis.

Cystitis

Cystitis is an infection that occurs in the urinary bladder and is sometimes simply referred to as a bladder infection. E. coli is the primary cause of this infection but others, such as Staphylococcus species, and members of Proteus, Enterobacter, Klebsiella, and Candida, have also been identified as organisms causing urinary bladder infections. The bacteria travel up the urethra, sometimes via a catheter, into the bladder, where they multiply and cause inflammation. If the infection remains untreated, it can spread to the kidneys, causing an even more serious infection. The helminth Schistosoma haematobium has been associated with urinary bladder infections and the human polyomaviruses JC and BK can cause hemorrhagic cystitis.

Pyelonephritis

Pyelonephritis is often referred to simply as a kidney infection, and this serious infection can cause extensive and permanent damage to the kidneys. The same organisms responsible for most cases of cystitis are also responsible for most kidney infections, with E. coli alone being responsible for more than 80% of these infections.

Leptospirosis

The spirochete Leptospira interrogans is a zoonotic organism that can cause a kidney infection or other nonspecific illnesses. Many mammals such as dogs, cats, and rats carry the organism, which can come in contact with humans through contaminated urine, direct contact with the animal, or through water or soil. Many cases of leptospirosis are asymptomatic and fewer than 100 cases are reported each year in the United States.

Glomerulonephritis

Glomerulonephritis, also referred to as Bright’s disease, involves inflammation and damage to the glomeruli of the kidneys. This is actually an immune complex disease that sometimes follows an oral streptococcal or viral infection. Antibody–antigen complexes are eventually filtered out in the kidneys, where they cause inflammation. This infection can cause some permanent damage to the kidneys and can be fatal.

Diagnosis of UTIs

Typically the detection/diagnosis process occurs in two stages. The first stage involves gathering a sample of urine for evaluation and the second stage involves testing the antibiotic sensitivity of any microorganisms that may be present. The collection of urine involves a procedure called a “clean catch,” wherein the patient thoroughly washes the genital area and then collects a midstream sample in a sterile container. The sample can then be both cultured for microbial growth as well as examined microscopically to determine the presence of microbes, pus, or blood. Typically the urine sample is streaked on a blood agar plate, using a special pattern to provide a semiquantitative analysis of the sample (Figure 15.3). If microbial growth occurs on the growth medium, the organisms can be tested with various antibiotics to identify the most effective one against a specific pathogen. This step is called a sensitivity test. The general term for the presence of bacteria in the urine is bacteriuria.

FIGURE 15.3 Method for streaking blood agar plates with a calibrated urine loop to produce isolated colonies with countable units. A, The drawing shows a streak pattern; B, the photograph shows a completed/incubated plate.

Risk Factors for UTIs

The risk factors for UTIs vary from individual to individual and from situation to situation; however, there appear to be certain factors that are common in many patients. The following groups exhibit unique risk factors:

• Diabetics: Patients with diabetes often have a higher risk for UTIs because of changes in the immune system that make them more vulnerable to infection.

• Patients with catheters: Patients with catheters in place for extended periods of time have an increased risk of infection of the urethra and ultimately the urinary bladder. About 20% of patients catheterized for more than 30 days will develop UTIs. The catheter itself can act as a location for the development of a biofilm (see Chapter 3, Cell Structure and Function), resulting in a greater diversity of species than may normally be found in the urinary bladder.

• Infants/children with abnormalities of the urinary tract:

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