Regarding enterotoxic colibacillosis of ETEC, which statement is true?

• A. It affects adults because receptors are present later in life.
• B. Oral infection leads to deep invasion of mucosa and ulceration.
• C. Oral infection leads to colonization of the intestine followed by toxin production.
• D. It does not cause secretory diarrhea.

Answer: (C)

ETEC causes illness by first attaching to the small-intestinal mucosa with fimbrial colonization factors, establishing colonization, and then releasing enterotoxins. This sequence—colonization of the intestine followed by toxin production—explains why the statement that oral infection leads to colonization followed by toxin production is true. The toxins (heat-labile and heat-stable) disrupt ion transport in enterocytes, triggering watery, secretory diarrhea. Because ETEC is noninvasive, it does not invade the mucosa or cause ulceration, so a claim about deep mucosal invasion is incorrect. It also causes secretory diarrhea, so denying secretory diarrhea is false. Disease is not limited to adults due to receptor timing; ETEC commonly affects travelers and young children across ages.