In a family of six (2 parents and 4 children), the youngest child catches measles infection. The parents are immune to the infection. On $3^{rd}$ and $5^{th}$ day of the infection of the first child, the two other children also suffer from measles. The secondary attack rate (SAR) of measles is:
The question asks for the Secondary Attack Rate (SAR) of measles within a family setting.
Calculating Measles Secondary Attack Rate (SAR)
The Secondary Attack Rate (SAR) is a measure used in epidemiology to determine the risk of contracting a disease after being exposed to it. It specifically looks at the proportion of susceptible individuals who get infected from a primary case.
The formula for SAR is:
$ SAR = \left( \frac{\text{Number of new cases among susceptibles}}{\text{Total number of susceptibles}} \right) \times 100\% $Applying the Formula to the Family
Let's identify the key components from the question:
- Total family members: 6 (2 parents, 4 children).
- Parents are immune, so they are not susceptible.
- The youngest child is the first case (index case).
- Total number of children = 4.
- Number of children who contracted measles after the first case = 2.
1. Identify Susceptibles: Since the parents are immune, only the children are susceptible. Total susceptible individuals = 4 children.
2. Identify Exposed Susceptibles: The index case is the first child. The remaining children are potentially exposed susceptibles. Number of exposed susceptibles = Total children - 1 (index case) = $4 - 1 = 3$ children.
3. Identify New Cases: Two other children contracted measles after the index case. Number of new cases = 2.
SAR Calculation
Now, we apply the SAR formula using the identified numbers:
$ SAR = \left( \frac{2}{3} \right) \times 100\% $ $ SAR = 0.6666... \times 100\% $ $ SAR \approx 66.67\% $Therefore, the secondary attack rate of measles in this family is approximately 66.67%.
Important Questions from General Epidemiology
Which of the following statements are correct for incidence rate?
1. It is useful for taking action to control a disease.
2. Rising incidence rates may indicate ineffectiveness of the current control programmes.
3. Fluctuation in incidence rate may indicate a change in aetiology of disease.
Select the answer using the code given below.
Consider the following definition :
"A high level of infection beginning early in life and affecting most of the child population, leading to a state of equilibrium such that the adult population shows evidence of the disease much less commonly than the children."
Which one of the following terms best fits this definition?
- In which one of the following study designs, the unit of study involves populations rather than individuals ?
- Which one of the following best explains the relationship among Prevalence (P), Incidence (I) and Duration (D) of a disease given the assumption that the population is stable?
- Which one of the following is a famous large prospective study that helped establish risk factors for coronary heart disease?
