**Question:** 200 people attended a party and some of them experienced diarrhoea after 24 hours. They consumed various food items like oyster, hamburger, ice-cream, and potato salad. What is the likely cause? 40 ill from 50 who ate oyster, 50 ill from 135 who ate hamburger, 60 ill from 140 who ate salad, and 49 ill from 115 who ate ice cream. 115

**Core Concept:**
Understanding the analysis of a food poisoning outbreak, considering the number of individuals affected after consuming specific foods and the total number of people who consumed those foods.

**Why the Correct Answer is Right:**

The correct answer is A (oyster) because the ratio of affected to consumed is the highest for oysters: 40/50 (80%). This suggests a higher probability of oysters being the causative agent. The lower ratios for other foods indicate that they are less likely causes.

**Why Each Wrong Option is Incorrect:**

B. The ratio for hamburger is 50/135 (37%), which is not as high as oysters. This makes option B less likely.
C. The ratio for salad is 60/140 (43%), which is lower than oysters but higher than other options. So, option C is incorrect due to overlapping with oysters.
D. The ratio for ice cream is 49/115 (42%), which is the second lowest ratio among options. This makes option D less likely.

**Clinical Pearl:**

In food poisoning outbreak investigations, ratios or percentages of affected individuals to the total number of those who consumed the food item can help determine the likely causative agent. However, ratios should be considered alongside the number of people affected compared to the total number consuming each food item, as seen with options A, C, and D.

**Explanation:**

In this scenario, we are assessing the likelihood of different foods causing food poisoning among the 200 individuals who attended the party. We calculate the ratio of affected individuals to the total number of individuals who consumed that food item.

1. For oysters: Affected (40) / Consumed (50) = 0.8 (80%)
2. For hamburger: Affected (50) / Consumed (135) = 0.35 (35%)
3. For salad: Affected (60) / Consumed (140) = 0.43 (43%)
4. For ice cream: Affected (49) / Consumed (115) = 0.42 (42%)

The highest ratio is observed for oysters (0.8, or 80%). This indicates oysters are more likely to be the cause of the outbreak and should be considered the most probable source of the contamination. In this case, the next highest ratio belongs to the hamburger (0