In a village of 100 children, 60% are immunized against measles. One child travelled outside and returned with measles and infected other 26 children. What is the secondary attack rate
**Question:** In a village of 100 children, 60% are immunized against measles. One child travelled outside and returned with measles and infected other 26 children. What is the secondary attack rate?
**Core Concept:** Secondary attack rate is the proportion of susceptible individuals in a population who become infected after an index case (in this case, the child who traveled outside and brought measles back) has occurred.
**Why the Correct Answer is Right:**
In this situation, we are given that 100 children are present in the village, and 60% (60 children) are immunized against measles. The remaining 40% (40 children) are susceptible to measles infection.
**Why Each Wrong Option is Incorrect:**
A. This option is incorrect because it does not account for the number of susceptible children in the population.
B. This option is incorrect because it does not consider the proportion of susceptible individuals in the village.
C. This option is incorrect because it does not take into account the number of susceptible children in the village.
D. This option is incorrect because it does not consider the proportion of susceptible individuals in the village.
**Why the Correct Answer is Right:**
After the index case (the child who traveled outside and brought measles back) infected 26 children, we need to find the number of susceptible children in the village. Since 40% of the children are susceptible, 40 children.
**Why Each Wrong Option is Incorrect:**
A. This option is incorrect because it does not take into account the proportion of susceptible children in the village.
B. This option is incorrect because it does not consider the number of susceptible children in the village.
C. This option is incorrect because it does not consider the proportion of susceptible children in the village.
D. This option is incorrect because it does not consider the proportion of susceptible children in the village.
**Secondary Attack Rate Calculation:**
The secondary attack rate is the proportion of susceptible individuals in the population who become infected after an index case has occurred. In this case, the index case infected 26 children out of 40 susceptible children, making a total of 40 children.
**Core Concept:**
The secondary attack rate is calculated as follows:
(Number of secondary cases / Total number of susceptible individuals) x 100
**Why the Correct Answer is Right:**
The secondary attack rate is calculated as (26/40) x 100 = 65%.
**Why Each Wrong Option is Incorrect:**
A. This option is incorrect because it does not account for the total number of susceptible individuals in the village.
B. This option is incorrect because it does not consider the proportion of susceptible children in the village.
C. This option is incorrect because it does not consider the total number of susceptible children in the village.
D. This option is incorrect because it does not consider the proportion of susceptible children in the village.
**Clinical Relevance:**
Knowing the secondary attack rate is essential for understanding the potential spread