Disease X is one that often results in severe illness, but never is fatal. On March 21, 1990, 30 students developed disease X among all students in an introductory epidemiology course at a university. (Assume all epidemiology students were exposed to the index case, the instructor.) Through antibody titers we were able to determine the following:  

a. of exposed students not infected = 40  
b. of exposed students with subclinical infection = 10 
c. of exposed students with mild symptoms = 10 
d. of exposed students with moderate symptoms = 10 
e. of exposed students with severe symptoms = 10

Using your knowledge of infectious disease epidemiology, quantify the pattern of disease X in this group, i.e., what are the infectivity, pathogenicity, and virulence of disease X?