Microsoft Word - Hwk 1.doc

1. A study published in 1990 (Am J Pub Health 80:p. 209-210) investigated the occurrence of HIV infection among prisoners in Nevada. Of 1105 prison inmates who were tested for HIV upon admission to the prison system, 36 were found to be HIV seropositive. All HIV seronegative prisoners were followed for a total of 1207 person-years and retested for HIV upon release from prison. Two of the uninfected inmates demonstrated evidence of new HIV infection. Assuming that the two prisoners were infected during their time in prison:
   1. Basedontheaboveinformation,
   2. calculatetheincidencerateofHIVinfectionamongprisonersintheNevadaprisons.
   3. Express the incidence rate calculated in part a in terms of cases per 1000 person-years.
   4. Calculate the prevalence of HIV infection among the incoming prisoners in the Nevada prisoners under study.
   5. What is the size of the population at risk for HIV at the beginning of the study?