How long after ingestion does food poisoning take to manifest at the latest?

There is no such thing as "the longest time for food poisoning to occur." Food poisoning usually develops within minutes to 72 hours after eating contaminated food—symptoms may appear as quickly as a few minutes to several hours, or as late as 1–3 days. If severe vomiting, diarrhea, or high fever occurs, immediate medical attention at a gastroenterology department is necessary.

After consuming food contaminated with bacteria such as Salmonella or E. coli, or food containing natural toxins, symptoms like nausea, vomiting, and abdominal pain may rapidly develop within minutes to hours, especially if the toxin is potent or consumed in large amounts. This commonly occurs after eating spoiled seafood or undercooked legumes.

If the ingested bacterial toxins multiply slowly or have a delayed effect, symptoms may not appear until 12 to 72 hours after consumption. These cases often present with diarrhea and low-grade fever. For example, eating refrigerated foods contaminated with Listeria may lead to delayed-onset food poisoning, which can be easily overlooked due to its late manifestation. Be aware of delayed reactions following meals.

In daily care, avoid spicy or irritating foods temporarily. Drink warm water in small amounts but frequently to prevent dehydration. Get adequate rest and avoid fatigue. Once symptoms improve, gradually resume intake of light, liquid foods. Closely monitor body temperature and bowel movements, and seek medical help promptly if any abnormalities occur.