What would be the effect on age-specific incidence rates of uterine cancer if women with hysterectomies were excluded from the denominator of incidence calculations assuming that most women who have had hysterectomies are older than 50 years of age?

1. The population of a city on February 15, 2005, was 36,600. The city has a passive surveillance system that collects hospital and private physician reports of influenza cases every month. During the period between January 1 and April 1, 2005, 2,200 new cases of influenza occurred in the city. Of these cases, 775 persons were ill with influenza according to surveillance reports on April 1, 2005. The prevalence rate of active influenza as of April 1, 2005, was:

Correct answer: 20 per 1,000 population

Solution: Prevalence rate = Number of cases / Total population Number of cases on April 1, 2005 = 775 Total number of cases between January 1 and April 1, 2005 = 2,200 Therefore, number of cases on January 1, 2005 = 2,200 – 775 = 1,425 Prevalence rate on April 1, 2005 = (775 / 36,600) x 1,000 = 20 per 1,000 population