Diverticulitis can cause urinary tract infections, and the mechanism is more alarming than most people expect. Rather than bacteria simply migrating from one organ to another through normal routes, the inflamed pouches of the colon can erode into the bladder wall, creating an abnormal tunnel called a colovesical fistula. Up to three-quarters of all colovesical fistulas trace back to diverticular disease, making it the single most common cause of this complication. The resulting UTIs tend to be stubborn, recurrent, and resistant to standard antibiotic courses because the underlying connection between bowel and bladder keeps reintroducing bacteria.
How Diverticulitis Creates a Path to the Bladder
The sigmoid colon, where diverticulitis most often flares, sits in the lower left abdomen in close contact with the urinary bladder. When a diverticulum becomes inflamed, the tissue around it swells, and if the inflammation is severe or repeated, it can progress into a localized abscess. That abscess, pressed against the bladder wall, can gradually break through both structures and form a fistula, typically on the left side of the bladder.1PubMed Central. Sigmoid diverticulitis mimicking a urinary bladder tumor: A rare case report Once that channel exists, intestinal contents, including fecal bacteria, flow directly into the urinary tract. No amount of antibiotic treatment will resolve the infections permanently as long as the fistula remains open.
Estimates of how often this happens vary. Colovesical fistulas appear in roughly 2% to 22% of people with a documented episode of diverticulitis, a wide range that reflects differences in how aggressively the condition is investigated. Among patients whose diverticulitis is severe enough to require surgery, around 10% to 15% have a fistula.2PubMed Central. Recurrent Urinary Tract Infections due to Asymptomatic Colonic Diverticulitis This is not a vanishingly rare complication. It is common enough that physicians are trained to consider it whenever someone presents with UTIs that keep coming back without an obvious urologic explanation.
Symptoms That Point to Something Beyond an Ordinary UTI
The hallmark signs of a colovesical fistula are not what you would expect from a typical bladder infection. Two symptoms in particular should raise immediate suspicion: pneumaturia, which is passing gas through the urine stream, and fecaluria, which is visible fecal matter in the urine. These are the most common presenting complaints and are sometimes the only signs, even when the underlying diverticulitis has been painless or so mild that the person never sought treatment for a bowel problem.2PubMed Central. Recurrent Urinary Tract Infections due to Asymptomatic Colonic Diverticulitis
Recurrent UTIs, lower abdominal pain, and painful urination round out the typical picture. Fever with persistent urinary discomfort is another red flag, particularly when standard antibiotic courses clear the infection temporarily but it returns within weeks.3PubMed Central. Colovesical Fistula due to Sigmoid Diverticulitis The pattern matters more than any single episode. A one-off UTI is unlikely to be diverticulitis-related. A string of infections over months, especially ones caused by gut organisms like Escherichia coli in someone with known or suspected diverticular disease, is a different story.
What catches many patients off guard is that the diverticulitis itself can be essentially silent. A case report documenting recurrent UTIs caused by asymptomatic colonic diverticulitis underscores that you do not need to be having abdominal pain or bowel changes for the colon to be quietly tunneling into the bladder.2PubMed Central. Recurrent Urinary Tract Infections due to Asymptomatic Colonic Diverticulitis This is one of the reasons the diagnosis is sometimes delayed: neither the patient nor the physician initially connects the urinary symptoms to a bowel problem.
Who Faces the Highest Risk
Men develop colovesical fistulas from diverticulitis more often than women, and the reason is anatomical. The uterus sits between the sigmoid colon and the bladder, acting as a physical buffer. In women who have had a hysterectomy, that buffer is gone, and the risk changes dramatically. A large population-based study found that women who had both a history of diverticulitis and a prior hysterectomy faced a roughly 25-fold increased risk of needing fistula surgery compared with women who had neither condition. Even without diverticulitis, hysterectomy alone raised the risk of fistula surgery about fourfold, and diverticulitis alone raised it about sevenfold.4PubMed. Influence of hysterectomy on fistula formation in women with diverticulitis
The practical takeaway for women with both a hysterectomy history and known diverticular disease is straightforward: recurrent UTIs in this group warrant early investigation for a possible fistula, even if there are no bowel symptoms. The usual assumption that a UTI is “just a UTI” deserves extra skepticism when both risk factors are present.
Age is another factor, though less sharply defined. Diverticular disease itself becomes more common with age, and the cumulative effect of repeated low-grade inflammation over years increases the chance that a fistula will eventually form. People who have had multiple documented episodes of diverticulitis carry more risk than those who have had a single isolated flare.
How Doctors Track Down the Fistula
When a colovesical fistula is suspected, the workhorse diagnostic tool is a CT scan of the abdomen and pelvis, ideally with oral or rectal contrast. Air inside the bladder on a CT image is one of the most telling findings, since air has no business being there unless something is allowing bowel gas to leak in. The scan can also show thickening of the bladder wall, thickening of the adjacent bowel, any abscess that has formed between the two structures, and sometimes the fistula track itself when contrast material is seen crossing from bowel to bladder.5PubMed Central. Four cases of enterovesical fistula and the importance of CT in the diagnosis Reported sensitivity for CT ranges from about 60% to 100%, with higher accuracy when contrast is used and the radiologist is specifically looking for fistula signs. When performed with dedicated contrast protocols, sensitivity climbs to 90% or higher.6Journal of Education and Teaching in Emergency Medicine. Sigmoid Diverticulitis Complicated by Colovesical Fistula Presenting with Pneumaturia
Beyond the CT scan, colonoscopy and cystoscopy (a camera look inside the bladder) are considered essential parts of the workup, not because they are better at finding the fistula itself, but because they help rule out a more sinister cause. Colon cancer and bladder cancer can also produce fistulas, and distinguishing a diverticulitis-caused fistula from a cancer-caused one changes the surgical plan entirely.7PubMed. Diagnosis and surgical management of colovesical fistulas due to sigmoid diverticulitis
The Poppy Seed Test
There is a surprisingly low-tech option for confirming a fistula: the poppy seed test. The patient swallows a small number of poppy seeds and then collects urine samples over the following hours. If poppy seeds appear in the urine, the fistula is confirmed, because there is no other way for seeds to travel from the gut into the bladder.8PubMed Central. Reviving the poppy seed test for the diagnosis of colovesical fistula: A case report from a single rural center experience The test is cheap, non-invasive, and has been shown to have high sensitivity.9PubMed. The poppy seed test for colovesical fistula: big bang, little bucks! It can be especially useful in settings where advanced imaging is not immediately available, or when CT findings are inconclusive and the surgeon needs another data point before committing to an operation.10PubMed. Oral intake of poppy seed: a reliable and simple method for diagnosing vesico-enteric fistula
Surgical Repair and What to Expect
Once a colovesical fistula is confirmed and cancer has been ruled out, surgery is the definitive treatment. Antibiotics alone cannot close the fistula. The standard operation involves removing the affected segment of the sigmoid colon (a sigmoidectomy), dividing the connection to the bladder, repairing the bladder wall, and then reconnecting the remaining colon ends.3PubMed Central. Colovesical Fistula due to Sigmoid Diverticulitis The bladder side of the fistula usually heals on its own once the source of contamination is removed, since bladder tissue regenerates well.
The surgery can be performed either as an open procedure or using minimally invasive (laparoscopic or robotic) approaches, depending on how much inflammation and scarring is present. Outcomes across large case series are generally favorable. A systematic review of the literature found that severe complications (those requiring a reoperation or intensive care) occurred in about 7% of cases, the 30-day mortality rate was around 1.5%, and fistula recurrence after repair was rare at roughly 0.5%.11PubMed. Burden of Colovesical Fistula and Changing Treatment Pathways: A Systematic Literature Review For most patients, surgery resolves both the fistula and the recurrent UTIs that prompted the investigation in the first place.
Some patients, particularly those who are elderly or have significant other medical conditions, may not be good candidates for immediate surgery. In those cases, doctors sometimes manage the situation conservatively with long-term antibiotics and close monitoring, accepting that the fistula will remain but trying to keep infections under control. This is a compromise, not a cure, and quality of life can suffer. Persistent symptoms like passing gas or fecal material in the urine take a real toll, and the ongoing risk of more serious infection remains.2PubMed Central. Recurrent Urinary Tract Infections due to Asymptomatic Colonic Diverticulitis
When the Problem Goes Unrecognized
The most dangerous scenario is when a colovesical fistula exists but nobody suspects it. Recurrent UTIs get treated with round after round of antibiotics, and the fistula quietly causes ongoing contamination of the urinary tract. In rare cases, this can escalate to life-threatening complications. One documented case involved a patient whose undiagnosed colovesical fistula led to emphysematous pyelonephritis, a severe kidney infection caused by gas-forming bacteria, complicated by a kidney abscess and acute renal failure.12PubMed Central. An Unusual Presentation of Diverticular Colovesical Fistula: Acute Renal Failure With Bilateral Emphysematous Pyelonephritis Sepsis is another feared endpoint when bowel bacteria have an open channel into the urinary system over a prolonged period.
The message from the clinical literature is consistent: multiple recurrent UTIs with no clear urologic explanation should prompt consideration of a colovesical fistula, particularly in anyone with known or suspected diverticular disease. The absence of classic bowel symptoms does not rule it out. Diverticulitis can be subclinical, and the first sign of trouble may be entirely urinary.
Can Diverticulitis Cause UTIs Without a Fistula
Most clinical literature focuses on the fistula pathway because it is the most dramatic and well-documented connection between diverticulitis and UTIs. But there is a plausible secondary route worth mentioning. A large diverticular abscess sitting adjacent to the bladder can compress or irritate the bladder wall and surrounding tissues without actually breaking through. This localized inflammation can theoretically impair normal bladder emptying, and incomplete emptying is a well-known risk factor for urinary infections in its own right. The evidence for this mechanism as a standalone cause of UTIs is thin compared with the fistula evidence, but it is a reasonable consideration in someone who has imaging showing a peri-colonic abscess near the bladder and develops a UTI during a diverticulitis flare.
The key distinction is clinical trajectory. A UTI caused by a temporary inflammatory effect during an acute diverticulitis episode should resolve once the diverticulitis is treated and should not recur in a pattern. Recurrent UTIs, especially with unusual symptoms like air in the urine, point toward a fistula and require a different level of investigation.
Why Urine Cultures Offer a Clue
Standard UTIs are typically caused by bacteria that live in the perineal area and ascend into the bladder through the urethra. Fistula-associated UTIs, by contrast, introduce organisms directly from the colon. In practice, both routes tend to involve the same dominant bacteria, since E. coli is abundant in both the gut and the perineal region. However, fistula-associated infections sometimes grow mixed flora or anaerobic bacteria that are unusual in a simple UTI. If a urine culture returns with an unexpected mix of gut organisms, especially in a patient with other risk factors, it is one more piece of the puzzle that should steer the clinician toward imaging.
The pattern of recurrence is often more informative than any single culture result. A person who clears an infection on antibiotics but develops a new one within a few weeks, caused by a similar or identical organism, is showing a pattern consistent with an ongoing source of contamination rather than repeated new infections. That distinction matters because the treatment strategy is fundamentally different: you cannot antibiotic your way out of a structural problem.
Living With Diverticular Disease and Protecting Your Urinary Health
If you have been diagnosed with diverticulosis (the presence of pouches) or have had one or more episodes of diverticulitis, there are a few things worth keeping in mind regarding your urinary tract. First, managing diverticular disease well reduces the risk of complications including fistulas. Staying ahead of flares, following up with your gastroenterologist, and not ignoring new or changing abdominal symptoms all help. Second, if you begin experiencing recurrent UTIs, mention your diverticular history to whoever is treating the infections. It is not always the first connection a clinician makes, especially if you are seeing a urologist who may not know your gastrointestinal history.
Third, pay attention to unusual urinary symptoms. Bubbles in the urine stream that are not caused by forceful urination, any visible debris in the urine, or a persistent foul smell that does not match a typical infection are all worth reporting promptly. These symptoms can be embarrassing to bring up, but they are the clinical clues that accelerate diagnosis and prevent the weeks-to-months of delayed treatment that some patients experience.
Finally, for women who have had a hysterectomy and also carry a diagnosis of diverticular disease, the elevated risk of fistula formation makes it worth discussing proactive monitoring with your physician. There is no screening protocol specifically for colovesical fistulas, but having a low threshold for imaging when urinary symptoms arise can make the difference between catching the problem early and catching it after kidney damage has occurred.