Causes and Risk Factors
In women, symptomatic UTIs are typically caused by the spread of potentially pathogenic bacteria from the bowel to the urinary tract (Hooton 2012; Schaeffer 2011b). Although UTIs can occur in anyone, certain factors increase risk, including female gender, sexual intercourse, family and personal history of UTIs, pregnancy, allergies, diabetes, abnormalities in the flow of urine, sustained urinary catheterization, incontinence, low estrogen levels, and antibiotic use.
UTIs are more common in women than men; the majority of females report having had a UTI by 32 years of age (Hooton 2012; National Kidney and Urologic Diseases Information Clearinghouse 2012a). This may be because: (1) women have shorter urethras than men, which makes it easier for bacteria to access their bladders, and (2) the urethral opening is closer to the external genitalia and anus, thus increasing the risk of bacterial cross-contamination (Mayo Clinic 2012a; University of Maryland Medical Center 2011; University Health Service 2012; National Kidney and Urologic Diseases Information Clearinghouse 2012a).
Sexual intercourse is a risk factor for UTIs (Hooton 1996, 2012; Mayo Clinic 2012a). This is particularly true for women that have sexual intercourse more than once per week (Hu 2004). Women that use diaphragms for contraception also have an increased risk of developing UTIs (Hooton 1996). A new sexual partner in the past year is another sexually related risk factor for UTI in women (Scholes 2005).
Having one or more first-degree female relatives (mother or sister) with a history of UTIs increases personal risk (Hooton 2012).
Having a personal history of UTIs, either recurrent or otherwise, is another major risk factor for the development of a subsequent UTI (Hooton 1996; Hu 2004; Scholes 2005).
Pregnancy appears to increase the risk that a UTI will spread and cause pyelonephritis, a serious infection of the kidneys associated with fever, chills, and flank pain. This is because pregnancy can cause hormonal changes, as well as shifts in the position of the urinary tract, which make it easier for bacteria to spread to the kidneys (University of Maryland Medical Center 2011; National Kidney and Urologic Diseases Information Clearinghouse 2012a).
Women who are allergic to compounds that may come in contact with the genital area, such as bubble baths, vaginal creams, and soaps may be at greater risk of developing UTIs because irritation of this sensitive region may allow bacteria access to the urinary tract (University of Maryland Medical Center 2011).
Patients being treated for diabetes have an increased risk of developing asymptomatic bacteriuria (bacteria in the urine that does not cause symptoms), UTIs, and pyelonephritis (Hu 2004; A.D.A.M. 2011). Diabetes impairs the immune system and makes it harder for the body to fight off infections (Mayo Clinic 2012a). In addition to the more common UTIs caused by E. coli, people with diabetes are also more likely to acquire UTIs caused by other bacteria, including Klebsiella and group B Streptococcus (Ronald 2002).
Urinary Flow Abnormalities
Disruptions in urinary flow can also predispose people to UTIs. Anatomical abnormalities that affect the urinary tract can lead to recurring urinary tract infections in children. Anything else that blocks the flow of urine, such as kidney stones, a narrow urethra, or an enlarged prostate, also increases the risk of UTI (Mayo Clinic 2012a; A.D.A.M. 2011; WomensHealth.gov 2008).
People who require a urinary catheter have a higher incidence of UTI (Ronald 2002). Use of a urinary catheter disrupts the body’s natural defense against bacterial infections and provides an easier route by which bacteria can travel to the bladder. As a result, it is recommended that urinary catheters be used for the shortest possible time to reduce the risk of UTIs (Hooton 2010, National Kidney and Urologic Diseases Information Clearinghouse 2012a; A.D.A.M. 2011; WomensHealth.gov 2008).
Incontinence is associated with an increase in UTIs (Hu 2004), as well as acute pyelonephritis (Scholes 2005).
Low Estrogen Levels
The risk of UTI increases after menopause as estrogen levels in the body drop. Estrogen is responsible for maintaining the health of vaginal walls; when estrogen levels are low, either due to menopause, surgery, or congenital problems, vaginal walls become thin, which increases susceptibility to invading bacteria (WomensHealth.gov 2008; University of Maryland Medical Center 2011). Some studies have found that estrogen prescriptions, such as creams and vaginal rings, may help prevent UTIs (Raz 2011).
Patients who have taken antibiotics recently may have an increased risk of developing a UTI. Antibiotics deplete the urinary tract of the beneficial bacteria Lactobacilli, which are protective against E. coli and other infectious bacteria (University of Maryland Medical Center 2011).