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Difficulty: MediumMeasures of Disease Frequency

A national infectious disease task force is evaluating the epidemiological characteristics of a newly identified strain of avian influenza (H7N9) that recently emerged in a specific geographic region. The task force reviews surveillance data compiled during the first 1212 months of the outbreak. The data are summarized in the table below:

Surveillance MetricNumber of Individuals
Total region population3,500,0003,500,000
Individuals tested for H7N9150,000150,000
Laboratory-confirmed H7N9 cases2,5002,500
H7N9-related hospitalizations1,0001,000
Total deaths (all causes)25,00025,000
H7N9-related deaths400400

Based on the surveillance data provided, which of the following best represents the case fatality rate of this newly identified avian influenza strain?

  1. A
    0.011%0.011\%
  2. B
    0.27%0.27\%
  3. C
    1.6%1.6\%
  4. 16.0%16.0\%Answer
  5. E
    40.0%40.0\%

Answer

16.0%16.0\%
The correct answer is 16.0%16.0\%. The case fatality rate (CFR) measures the severity or lethality of a disease. It is calculated by dividing the number of deaths caused by a specific disease by the total number of people diagnosed with that disease in the same period. In this surveillance scenario, there were 400400 deaths directly attributed to H7N9 and a total of 2,5002,500 laboratory-confirmed cases. Therefore, the CFR is 4002,500\frac{400}{2,500}, which equals 0.160.16, or 16.0%16.0\%.

Step-by-Step Solution

1
Identify the epidemiological formula for Case Fatality Rate (CFR).
CFR=Deaths from the diseaseTotal confirmed cases of the disease×100%\text{CFR} = \frac{\text{Deaths from the disease}}{\text{Total confirmed cases of the disease}} \times 100\%
CFR measures the lethality of a condition by assessing what proportion of diagnosed individuals ultimately die from it.
2
Extract the necessary data points from the surveillance table.
Deaths from H7N9 = 400400. Laboratory-confirmed H7N9 cases = 2,5002,500.
Only the specific deaths caused by the disease and the total number of individuals definitively diagnosed are required for the calculation.
3
Perform the calculation to find the percentage.
4002,500×100%=0.16×100%=16.0%\frac{400}{2,500} \times 100\% = 0.16 \times 100\% = 16.0\%
Dividing the specific deaths by the total confirmed cases yields the correct case fatality rate.

Key Concept

The Case Fatality Rate (CFR) is a measure of disease severity, defined as the proportion of fatal cases among those diagnosed with the disease during a specified time period.
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Topics

Measures of Disease Frequency

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