A urinary tract infection (UTI) occurs when bacteria colonize any part of the urinary system, most commonly the bladder. While classic symptoms involve urination, many people experience a feeling of general illness that includes an upset stomach, which can manifest as nausea, vomiting, abdominal pain, or diarrhea. This connection between a localized urinary infection and widespread gastrointestinal (GI) distress stems from biological responses to infection and sometimes from the treatment itself.
The Direct Link: How UTIs Impact the Digestive System
The primary way a UTI can cause an upset stomach is through the body’s systemic inflammatory response to the bacterial invasion. When the immune system detects the infection, it releases signaling molecules called cytokines to fight the bacteria, even if the infection is still confined to the bladder. These inflammatory chemicals travel through the bloodstream and can trigger generalized symptoms like malaise, fatigue, and nausea by affecting the brain’s vomiting center.
The physical proximity of the bladder to the lower digestive tract also contributes to discomfort. The organs in the pelvic region share many of the same nerve pathways, which can lead to a phenomenon known as referred pain. An intense inflammatory signal from the infected bladder can be misinterpreted by the brain as pain or discomfort originating from the nearby bowel, resulting in lower abdominal cramping or generalized GI upset.
A frequent cause of GI distress during a UTI is the antibiotic medication prescribed for treatment. Antibiotics kill bacteria, but they do not discriminate between the harmful bacteria causing the UTI and the beneficial bacteria residing in the gut. This disruption of the natural gut microbiome can lead to common side effects such as diarrhea, stomach cramps, and nausea or vomiting. These side effects are temporary and resolve once the course of treatment is complete.
Distinguishing a UTI from a Kidney Infection
While a simple UTI confined to the bladder (cystitis) may cause mild nausea due to systemic inflammation, severe GI symptoms often signal a more serious progression of the infection. A kidney infection, known as pyelonephritis, occurs when the bacteria travel up the ureters and infect one or both kidneys. Because the kidneys are organs with a systemic function, their infection triggers a much stronger, body-wide reaction that makes severe nausea and persistent vomiting far more likely.
The location of the pain is a major distinguishing factor between a lower UTI and a kidney infection. A bladder infection typically causes pain or pressure in the lower abdomen or pelvic region, just above the pubic bone. In contrast, a kidney infection causes pain in the flank, which is the area on the side of the body between the ribs and the hip, or in the upper back.
Pyelonephritis requires immediate treatment to prevent complications. Beyond severe nausea and vomiting, a kidney infection is characterized by a high fever, often exceeding 101°F (38.3°C), and shaking chills. While a lower UTI may cause a low-grade fever, the combination of systemic illness, flank pain, and severe GI upset indicates the infection has reached the upper urinary tract.
Other Common Symptoms of a Urinary Tract Infection
Beyond the potential for stomach upset, a lower UTI is primarily identified by a set of classic symptoms related directly to the bladder and urethra. The most common sign is dysuria, which is a burning or painful sensation during urination. This discomfort occurs as the inflamed lining of the urinary tract comes into contact with urine.
Infection irritates the bladder wall, leading to urinary urgency, a sudden, compelling need to urinate. This occurs alongside urinary frequency, requiring multiple trips to the bathroom, even if only small amounts of urine are passed. The urine may also appear cloudy or have a strong, foul odor due to the presence of bacteria and white blood cells.
When to Seek Immediate Medical Care
Recognize when a urinary infection requires prompt medical attention. Persistent vomiting that prevents keeping down fluids is a red flag, as this quickly leads to dehydration and electrolyte imbalance, complicating the infection. Dehydration can also worsen feelings of nausea and malaise.
Symptoms that point toward a kidney infection should be treated as an emergency. These include a temperature of 101°F (38.3°C) or higher, the onset of severe back or flank pain, or uncontrollable shaking and chills. These signs suggest that the infection has become systemic and may require intravenous antibiotics to prevent further complications.
In older adults, confusion or an altered mental state can be the only noticeable symptom of a severe UTI or kidney infection, even without a high fever or specific urinary complaints. Anyone experiencing these serious symptoms or observing blood in their urine should seek medical care immediately. A healthcare provider can perform a urinalysis to confirm the infection and prescribe the appropriate antibiotic regimen to clear the bacteria and prevent spreading.