What is a urinary tract infection?

Urinary tract infections¹ (UTIs) are bacterial infections that can occur in any part of the urinary tract. The bacteria that cause these infections often originate on the skin or rectum and enter the urinary tract through the urethra (the tract’s opening).

The urinary tract is equipped to deal with coming into contact with bacteria. Urine flows from the kidneys to the bladder through tubes called ureters. When you urinate, any bacteria that have entered your urinary tract are flushed out of your body. When bacteria from outside the body enter the urethra, however, it can potentially cause an infection.

UTIs most commonly occur in the lower urinary tract, affecting the urethra or the bladder (called bladder infections). Women are more likely to develop UTIs than men because their urethras are shorter, making it easier for bacteria to enter and infect the urinary tract.

While common, UTIs are uncomfortable. They can cause painful, burning sensations and increase the feeling of needing to urinate. Rarely, UTIs can become severe and spread to the kidneys. A kidney infection—called pyelonephritis—is serious and requires medical treatment.

How common are UTIs?

UTIs are common—particularly among women. Approximately 40–60% of women² develop a UTI during their lifetime; the majority of these are bladder infections. Between 20–40% of women³ who have at least one UTI in their lives will develop another one in the future.

While men are less likely to get at least one UTI than women, they are highly likely to develop another UTI if they have already had one. This is due to the fact that the bacteria that cause these infections tend to reside in the prostate once they have entered the body.3

Asymptomatic bacteriuria is also common among older adults. The condition occurs when urinary bacteria levels are elevated but do not cause the common symptoms of a UTI. This is common among older adults, occurring in 6–16%⁴ of women over the age of 65 and 20% of women older than 80.

If you experience frequent UTIs (3 or more per year), it’s important that you see your healthcare provider. Not only can they help you manage the uncomfortable symptoms of these infections, but they can also conduct testing to determine the reason for your recurrent UTIs.

UTI causes

The urinary tract is made up of three structures: the kidneys, ureters (ducts through which urine travels to the bladder), and the bladder (a hollow organ that stores urine from the kidneys before being disposed of through urination). This system’s job⁵ is to make, store, and transport urine. When urination occurs, waste products—as well as bacteria that have entered the urinary tract—are passed from the body through the urethra.

Normally, the urine does not contain any bacteria. The one-way flow of urine from the kidneys out of the body helps stop bacteria from collecting and prevent infections from occurring.

Sometimes, however, these defenses fail. Urinary tract infections begin⁶ when bacteria enters the urinary tract through the urethra. These bacteria then begin to multiply in the urinary tract, creating an infection.

Different types of UTIs

There are multiple ways of classifying UTIs. One way of distinguishing between different types⁷ of UTIs is according to where the infection occurs.

Three main types of urinary tract infections are:

• Cystitis (bladder infection): Cystitis⁸ is most commonly caused by the bacterium Escherichia coli (though some other types of bacteria may be responsible). These bacteria, more commonly known as E. coli, are frequently found in the gastrointestinal (GI) tract.

In some cases, having sex may play a role in the development of cystitis. This does not mean that it is a sexually transmitted infection (STI)—you can get cystitis even if you aren’t sexually active. Like any other UTI, it is caused by the transmission of bacteria into the urinary tract.

Women have a higher risk than men for getting cystitis because of the shorter distance between their urethra and anus and the urethral opening to the bladder.

• Urethritis (urethra infection): Urethritis commonly occurs when bacteria originating in the GI tract are spread from the anus to the urethra. Because of the shorter distance between the vagina and the urethral opening, women may also develop urethritis due to bacterial STIs, such as gonorrhea, chlamydia, or herpes.

This infection is usually accompanied by discharge and a burning sensation during urination.

• Pyelonephritis (kidney infection): Pyelonephritis⁹ is a serious condition that occurs when a urinary tract infection travels to one or both of the kidneys. It can cause pain in the upper back and side, shaking and chills, nausea, vomiting, and a high fever. Kidney infections require urgent medical care.

Risk factors for UTI

Some factors¹⁰ may increase your risk of getting a UTI, including:

• Having had a UTI in the past
• Being sexually active (especially having a new sexual partner)
• Age: the two groups most likely¹¹ to get UTIs are young children and older adults

• Structural problems or abnormalities in the urinary tract, such as an enlarged prostate or a congenital defect (abnormality present at birth)
• Blockages in the urinary tract, which may be caused by an enlarged prostate or kidney stones
• Having a suppressed immune system
• Sexually transmitted infections¹²

• Catheter use
• Living in group care facilities (for older adults)

UTI in women

Women and girls face a higher risk¹³ for developing UTIs than males. This is partially due to anatomical¹⁴ differences: the shorter distance between a woman’s urethral opening and bladder makes it easier for bacteria to reach the bladder, and the proximity of the urethra to the rectum increases the chances that infectious bacteria will spread.

Some risk factors for UTI that are specific to women¹⁵ include:

• Changes in the naturally occurring bacteria in the vagina: This can be caused by things like menopause or the use of spermicides.
• Sexual activity: Women who are sexually active tend to have UTIs more frequently than those who are not.
• Certain types of birth control, such as diaphragms and spermicidal products, can increase the risk for UTI

UTI in men

Urinary tract infections are less common in men than in women. When they do occur, UTIs are more likely to affect older men than younger ones.

UTIs can develop¹⁶ in men in the urethra, bladder, prostate, or kidneys.

Several factors can increase the risk of bladder infection in men¹⁷:

• Having an enlarged prostate (called benign prostatic hyperplasia, or BPH), which can prevent the bladder from emptying completely
• An abnormal narrowing of the urethra (urethral stricture)
• Kidney stones
• Having recently undergone a urinary tract procedure, such as catheterization or cystoscopy

UTI symptoms

UTIs don’t always cause¹⁸ noticeable signs or symptoms. When they do, UTIs can range from being mildly annoying to extremely uncomfortable.

Common symptoms of urinary tract infections include:

• Feeling a strong, persistent need to urinate, even with an empty bladder
• Frequent urination (and often passing only small amounts of urine)
• Burning or pain when urinating
• Cloudy and/or strong-smelling urine
• Red, bright pink, or cola-colored urine (indicates blood in the urine)
• Pelvic pain (in women)

The symptoms of a bladder infection are similar to those of UTIs in general, with the addition of pressure or cramping in the lower abdomen or groin.

The symptoms of kidney infections¹⁹ are much more severe, and can include:

• Chills
• Fever
• Pain in the lower back or side
• Nausea and/or vomiting