What is the minimum number of organisms per gram in stool required for diagnosis of C. perfringens?

• A. >100 organisms/g
• B. >1 million organisms/g
• C. >10,000 organisms/g
• D. >10 million organisms/g

Answer: (B)

The main idea is that diagnosing C. perfringens gastroenteritis relies on a high bacterial load in the stool, because many people can shed small amounts without being sick and the illness is linked to overgrowth with toxin production. C. perfringens causes disease when enough organisms are present to produce enterotoxin during sporulation in the gut, so a high stool count supports an active infection. The commonly used diagnostic threshold is more than 1,000,000 organisms per gram of stool, which helps distinguish true infection from incidental carriage. Counts far lower than this are not as convincing for disease, while the >1,000,000/g threshold specifically reflects clinically significant overgrowth.