C. diff (Clostridioides difficile) is a bacterial infection that causes watery diarrhea, often three or more times a day, along with stomach pain and tenderness. Symptoms typically begin within 5 to 10 days of starting an antibiotic, though they can appear as early as the first day of treatment or up to three months later. In the United States, there were roughly 117 cases per 100,000 people reported at CDC surveillance sites in 2023, making it one of the most common healthcare-associated infections.
The Core Symptoms
The hallmark of a C. diff infection is frequent, watery diarrhea. Mild to moderate cases typically involve three or more loose stools per day, sometimes accompanied by cramping, bloating, or general abdominal discomfort. The stool often has an unusually foul smell that many patients and healthcare workers describe as distinctive.
Fever can accompany the infection, generally above 100.4°F (38°C), though not everyone develops one. Some people also experience nausea, loss of appetite, and dehydration from the fluid loss. Dehydration itself brings its own set of problems: dizziness, dry mouth, reduced urination, and fatigue. If the diarrhea is persistent, these secondary effects can become serious quickly, especially in older adults.
How Symptoms Progress in Severe Cases
Most C. diff infections stay in the mild-to-moderate range, but severe cases look markedly different. The diarrhea becomes more frequent (10 to 15 episodes per day is not unusual), and it may contain blood. Abdominal pain shifts from general discomfort to intense tenderness, and fever climbs higher. The body mounts a strong inflammatory response, which shows up in blood work as a very high white blood cell count.
The most dangerous complication is toxic megacolon, where the colon becomes severely dilated and essentially stops functioning. Signs include a visibly swollen abdomen, a heart rate over 120 beats per minute, high fever, mental confusion, and low blood pressure. This is a medical emergency. A ruptured colon can cause life-threatening internal bleeding and widespread infection (sepsis). Toxic megacolon is rare, but recognizing its warning signs matters because it escalates fast.
Why Antibiotics Are the Main Trigger
C. diff bacteria thrive when the normal balance of gut bacteria gets disrupted, and antibiotics are the most common disruptor. The antibiotic classes most frequently linked to C. diff include broad-spectrum penicillins (like piperacillin/tazobactam), cephalosporins (like ceftriaxone), fluoroquinolones (like ciprofloxacin and levofloxacin), carbapenems, and clindamycin. These drugs are effective at treating other infections, but they also wipe out protective bacteria in the gut, giving C. diff room to multiply and produce toxins that damage the intestinal lining.
Hospital stays longer than three days and regular use of acid-reducing medications (proton pump inhibitors) also increase risk. The infection is more common in people over 65, and incidence rises with age. For older adults, especially those undergoing cancer treatment, C. diff symptoms can be hard to distinguish from the gastrointestinal side effects of chemotherapy or radiation, which sometimes delays diagnosis.
How C. Diff Is Diagnosed
Diagnosis starts with a stool sample. Laboratories use a combination of tests to confirm the infection. A rapid screening test checks for a protein the bacteria produce, but this test alone can’t distinguish between harmless colonization and active infection. So it’s paired with a toxin test that looks for the specific toxins (A and B) that C. diff releases to damage the gut. Toxin B is the primary target, since some disease-causing strains don’t produce toxin A. Results from the rapid screen come back in under an hour, while toxin testing may take longer.
Testing is only recommended on loose, unformed stool. If your stool is solid, C. diff is unlikely to be the cause of your symptoms, and testing on formed stool can produce misleading results.
Recurrence Is Common
One of the most frustrating aspects of C. diff is how often it comes back. Between 15% and 30% of patients who respond well to initial treatment experience a recurrence, with symptoms returning days to weeks after finishing their medication. The recurrence typically looks the same as the first episode: watery diarrhea, cramping, and sometimes fever.
What makes recurrence especially concerning is that the risk compounds with each episode. After a first recurrence resolves, roughly 40% of patients go on to have a second. For those who have already had two or more recurrences, the chance of yet another episode climbs to 45% to 65%. Each round further disrupts the gut’s microbial balance, creating a cycle that becomes progressively harder to break. Newer treatments, including fecal microbiota therapies, specifically target this cycle by restoring protective gut bacteria.
Symptoms That Need Urgent Attention
Mild diarrhea during or after a course of antibiotics isn’t always C. diff, but certain patterns should prompt a call to your doctor: diarrhea three or more times a day for two or more days, any blood in the stool, fever alongside diarrhea, or significant abdominal pain. If you notice a swollen abdomen, a racing heartbeat, confusion, or dizziness severe enough that you feel faint, those are signs the infection may have progressed to a dangerous stage and needs immediate medical evaluation.
Older adults and people with weakened immune systems are at higher risk for rapid progression. In these groups, even moderate symptoms warrant early testing, since delayed treatment increases the likelihood of complications and recurrence.