Gallbladder infections are almost always caused by a blockage that traps bile inside the gallbladder, creating a breeding ground for bacteria. Gallstones are responsible in roughly 90% of cases, but infections can also develop without stones, particularly in people who are critically ill. Globally, gallbladder and biliary diseases affect over 73 million new cases per year, making this one of the most common reasons for emergency abdominal surgery.
How Gallstones Trigger Infection
The gallbladder stores bile, a digestive fluid produced by the liver. After you eat, the gallbladder contracts and pushes bile through a small tube called the cystic duct into the intestine. A gallstone can lodge in that duct and block the exit, trapping bile inside.
Once bile is trapped, pressure builds against the gallbladder wall. The stagnant bile irritates and inflames the lining, and bacteria that normally pass through the biliary system in small numbers begin to multiply. The most common culprits are gut bacteria: E. coli and Klebsiella pneumoniae show up most frequently in infected bile samples, along with certain streptococcal species. In some cases, a strain of E. coli already resistant to common antibiotics is involved, which can complicate treatment.
This sequence of blockage, bile stasis, inflammation, and bacterial overgrowth is the classic pathway behind acute cholecystitis, the medical term for gallbladder infection.
Gallbladder Infection Without Stones
About 5% to 10% of gallbladder infections happen without any gallstones at all. This form, called acalculous cholecystitis, tends to strike people who are already seriously ill. Patients in the ICU recovering from major surgery, severe burns, extensive trauma, stroke, heart attack, or sepsis are at the highest risk. Long periods of fasting, receiving nutrition through an IV rather than eating, and drastic weight loss can all set the stage.
Without the mechanical squeeze that eating triggers, bile sits in the gallbladder for too long. The gallbladder wall becomes sluggish, blood flow to the tissue decreases, and bacteria take hold. Because the patients who develop this form are already fighting other serious conditions, acalculous cholecystitis is often harder to diagnose and carries a higher complication rate.
Other Blockages That Can Cause Infection
Gallstones aren’t the only thing that can block bile flow. Tumors in the bile ducts or gallbladder, whether cancerous or not, sometimes obstruct the same pathways. People with a history of primary sclerosing cholangitis (chronic inflammation and scarring of the bile ducts), liver flukes (parasites found in parts of Asia), chronic viral hepatitis, cirrhosis, or cysts in the bile duct all face elevated risk. The mechanism is the same: anything that prevents bile from draining normally raises the chance of infection.
Dietary and Lifestyle Risk Factors
The foods you eat play a measurable role in gallstone formation, which is the first domino in most gallbladder infections. A large analysis of three prospective studies found that people who ate the most ultra-processed foods had a 29% higher incidence of gallstone disease compared to those who ate the least. Each additional daily serving of ultra-processed food raised gallstone risk by about 2.8%. Sugar-sweetened beverages and artificially sweetened beverages drove most of that increased risk.
Rapid weight loss is another well-established trigger. When the body breaks down fat quickly, the liver secretes extra cholesterol into bile, which can crystallize into stones. The National Institute of Diabetes and Digestive and Kidney Diseases recommends losing no more than 5% to 10% of your starting body weight over a six-month period to minimize gallstone formation. Crash diets and very low-calorie regimens carry a particularly high risk.
Other known risk factors include obesity, being over 40, female sex hormones (estrogen increases cholesterol in bile), pregnancy, and a family history of gallstones.
What Happens If It Goes Untreated
A gallbladder infection that isn’t treated can escalate quickly. The trapped, inflamed tissue can lose its blood supply and become gangrenous. Perforation, where the gallbladder wall actually ruptures, occurs in roughly 2% to 11% of acute cholecystitis cases. When that happens, infected bile leaks into the abdominal cavity, and complication rates climb sharply: one study found that among patients with gallbladder perforation, 57.7% experienced serious complications and 9.5% died. Preoperative sepsis was the single strongest predictor of mortality.
Another feared complication is ascending cholangitis, where infection climbs from the blocked area up through the entire biliary tree toward the liver. This can cause high fevers, jaundice (yellowing of the skin and eyes from bile pigments backing up into the bloodstream), and septic shock.
How Gallbladder Infection Is Diagnosed
Abdominal ultrasound is the first-line test and the most practical. It is noninvasive and 90% to 95% accurate at detecting gallstones. If the ultrasound shows thickened gallbladder walls, surrounding fluid, or stones lodged in the cystic duct, the diagnosis is often straightforward.
When ultrasound results are inconclusive but suspicion remains high, a HIDA scan is the next step. This nuclear medicine test tracks a radioactive tracer as it moves through the biliary system. If the tracer fills the liver and bile ducts but never enters the gallbladder, it confirms that the cystic duct is completely blocked, a finding that is close to 100% accurate for diagnosing acute cholecystitis. The same scan can also detect acalculous cholecystitis by measuring how well the gallbladder empties, with about 95% accuracy.
Why Bile Stasis Is the Common Thread
Whether the cause is a gallstone, a tumor, a parasitic infection, or prolonged fasting in a critically ill patient, the underlying mechanism is the same. Bile that cannot flow becomes a stagnant reservoir. Bacteria colonize it, the gallbladder wall swells and weakens, and without intervention the infection can spread or the organ can rupture. Understanding that stasis is the root cause explains why so many different conditions, from diet choices to ICU stays, can lead to the same dangerous outcome.