The team members arrive in Rhode Island on March 1st. They discover 13 individuals who met the clinical/laboratory case definition with dates of rash onset in February. Ten of these 13 are Rhode Island residents, the other three are residents of neighboring states who were seen and treated at Brown University Medical Center in Providence, RI. Nine of these 10 were still ill as of March 1. The tenth, the probable index case for the outbreak, was a teenager who had traveled to Europe and returned three days prior to her rash onset. She had recovered from her illness by the time the investigative team arrived.
For the purposes of this exercise, use one million for the Rhode Island state resident population.
Note: remember to express all rates (incidence is a rate) per unit of population and per unit of time. Prevalence (a ratio) needs only to be expressed per unit of population.
1) What was the prevalence of measles in Rhode Island as of March 1st?