Disease X is a respiratory infection that often results in severe illness, but i
ID: 180165 • Letter: D
Question
Disease X is a respiratory infection that often results in severe illness, but is never fatal. On March 21, 2002, 30 students enrolled in a public speaking course developed Disease X. NOTE: assume all the students were exposed to the index case, the professor. Subclinical means the person does not have symptoms of illness, but laboratory tests indicate infection. Through antibody titers, the following was determined:
# of exposed students not infected 40
# of exposed students with subclinical infections 10
# of exposed students with mild symptoms 10
# of exposed students with moderate symptoms 10
# of exposed students with severe symptoms 10
1.) What is the attack rate?
2.) What is the pathogenicity of disease X?
3.) What is the virulence of disease X?
Explanation / Answer
Please find the answers below:
Answer part 1) Attack rate :
The attack rate of a disease is defined as the fraction of appearance of new cases of a disease in a population relative to the total number of pre-exisiting disease cases in that population.
According to the information, the number of new potential cases appeared (sub-clinical) are : 10.
The number of individuals at risk are (mild, moderate and severe symptoms) : 10+10+10 or 30
Thus, attack rate = 10/30 or 1/3 or 33.3%
Answer part 2: Pathogenicity :
Pathogenicity of the disease X is defined as number of new clinical cases appeared in the population relative to the total number of individuals in the population.
Thus, the total number of individuals in the population is: 40+10+10+10 OR 70
The number of individuals with clinical symptoms (mild to severe) of disease: 10+10+10 OR 30
Thus, the pathogenicity of the disease = 30/70 or 42.8%
Answer part 3) Virulence of disease:
Virulence of disease is defined as the extent or degree of damage caused by the disease in an individual, usually evalulated in terms of qualitative assessement of severe pathological symptoms due to infection. Thus, the number of virulent infections in this case is 10 and the total population size is 70.
Thus, virulence of the disease X is: 10/70 OR 14.3%.