1 An epidemiological investigation was begun on July 1, 2000 among a population of 1,000 individuals. Three individuals were found to have leukemia on July 1st. During the ten-year follow-up period, five new cases of leukemia were diagnosed. Among the eight leukemia cases, four deaths occurred during the ten-year follow-up period. Two additional individuals, neither of whom had leukemia, were lost to follow-up at some point during follow-up. None of the remaining 990 study participants became ill, died, or were lost to follow-up during the follow-up period. The diagram below indicates the experience of the 10 study participants, using the following symbols: * :case recognition (diagnosis of leukemia) *< :onset of leukemia was prior to start of study period ---:observation period during follow-up X :status at termination of observation (i.e., alive, dead, lost) case 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 1 --- --*-- ----- ----- ----- ----- ----- ----- ----- ----2 --- ------ ----- --*-- ----- ----- ----- ----- ----- ----3 *<-- ------ ------ ----- ----- ----- ----- ----- --X 4 --- ------ ----- ----- --X 5 --- ------ ----- ----- ----- ----- --*-- --X 6 --- ------ ----- ----- ----- ----- ----- ----- ----- --*-7 --- --*-- ----- ----- --X 8 *<-- ------ ------ ----- ----- ----- ----- ----- ----- ----- ----9 --- ------ ----- ----- ----- ----- ----- --X 10 *<-- ------ ------ --X What was the prevalence of leukemia on January 1, 2005? What was the cumulative incidence of leukemia during the 10-year follow-up period? What was the incidence rate of leukemia during the 10-year follow-up period? What was the case fatality rate during the 10-year follow-up period? 2010 --X --X --X --X QUESTION 2 Suppose that you are following a group of children for the development of asthma over a one- year period. You identify 100 children on January 1st, screen them for asthma, and set up a monitoring program to check on their status on a monthly basis. Five children are considered prevalent cases because they were diagnosed with asthma before January 1st. Ten children develop asthma on March 1st and another ten children develop asthma on July 1st. Another 10 children who remain healthy were followed for six months and then were lost to follow-up. All of the remaining children did not develop asthma and were not lost to follow-up. Follow-up ended on December 31st. 1 What was the prevalence of asthma on June 1st? 2 What was the prevalence of asthma on September 1st? 3 How many person-months of observation were accrued by this population? alive alive dead lost dead alive dead alive lost dead What was the incidence rate of asthma in this population for the one-year period? QUESTION 3 How does each of the following conditions influence the prevalence of a disease in a population? For each scenario, assume that no other changes occur. Your choices are: increases prevalence, decreases prevalence, or has no effect on prevalence. 1 A treatment is developed that prolongs the life of people suffering from the disease 2 A new measure is developed that prevents new cases of disease from occurring 3 There is immigration of a large number of healthy people into the population. The case-fatality rate for the disease increases