MEASURES OF DISEASE OCCURRENCE

Read Gordis Chapter 4 o answer the qns below ....Epidemiology by Leon Gordis, 5^th Edition, ISBN-13 978-1455737338.

What pattern of occurrence is shown by Disease X? Is it increasing or decreasing in the community? Is it affecting a large part of the population or a small fraction? Does it affect particular subgroups such as children, Asians, individuals aged 40 to 49, or lumber mill workers? Does Community A have the same experience with the disease as Community B? The answers to these and other epidemiologic questions start with the use of the measures introduced in this exercise.

To begin to answer these questions we need:

1. an agreed-upon definition of the disease of interest;

2. a count and characterization of persons already affected by the disease (prevalence) or who developed the disease (incidence);

3. a count and characterization of the total population from which the diseased group came; and

4. knowledge of the calendar time of recognition or occurrence of the disease.

Diagnosis of Disease

To study the frequency or distribution of a given disease, it is important that as much as possible the disease actually present (or occurring) be discovered and that as few as possible persons without the disease be mistakenly included in the diseased group. These determinations may depend upon such things as the ability of health practitioners to "recognize" the disease, characteristic pathology discovered at autopsy, results of laboratory test, or special criteria and rules for diagnosis developed for special studies.

Question 1 - What is the incidence of the disease in this group?

Question 2 - What is the prevalence at Point A? Point B? What might account for the difference?

Question 3 - When is incidence most useful? Prevalence?

Question 4 - From Figure 2, what is the person-time incidence of Disease O in this group?

Question 5 - Do you think that incidence or prevalence numbers are shown in Table 1?

Question 6 - How many cases of tuberculosis were reported in 2013? To you think that this represents a decrease from 2009? Why or why not?

Question 7 - There were 62,192 deaths (all causes) during the period January 1 through December 31, 1977 in residence of Los Angeles County (estimated total population 7,000,000). What was the crude mortality rate for 1977?

Question 8 - Of 9,333 deaths certified as acute myocardial infarction in 1969, 593 occurred among white males aged 45 to 54 years. There were 366,899 white males aged 45 to 54 in the population. Calculate this age-, ethnic group-, and sex-specific mortality rate.

Question 9 - Of the 62,192 total deaths in Los Angeles in 1977, 11,343 were certified as due to cancer. What is the proportionate cancer mortality? Does this agree with the American Cancer Society's "one in six"?

Proportionate mortality (or morbidity) may be measured on an age-, race-, or sex-specific basis. Proportionate mortality is particularly useful when the size and the age, race, sex, and other characteristics of the population at risk are unknown. Measurement of rates is desirable whenever the characteristics of cases (and deaths) and the characteristics of the population are known, as rates measure the risk of an event in a defined community.

Case fatality expresses the risk of death among persons who have a disease, i.e. the proportion of deaths among cases.

Question 10 - In a recently reported outbreak of 85 cases of Salmonella infection in an institution, two died as a result of the infection.

1. What is the case fatality?

2. What other information is needed to assess the magnitude of the problem, i.e. the institutional risk of the disease? The institutional mortality?

Question 11 - During one year, 106 persons were admitted to Northeast Community Hospital and diagnosed as having lung cancer. Of these cases, 60 died and 46 were discharged alive.

1. What is the institutional case fatality for this group?

2. Does this measured lung cancer fatality?

Question 12 - Why might the perinatal mortality be better to use? When would you use it?

Question 13 - Do you think the denominator for maternal mortality is appropriate? Why or why not? What would you suggest is a better one?

Question 14 - Name some of the diseases listed in Figure 6 that must be reported immediately. Why are they of "urgent concern", compared, for example, to AIDS?

Question 15 - Do you think that health departments receive accurate counts of these diseases? What characteristics of a disease might lead to its accurate reporting? In the case of inaccuracies, do you think there would be over-reporting or under-reporting? Why?

Question 16 - What are some of the problems of establishing and maintaining a disease registry? With the use of a disease registry to determine a morbidy rate?

The population at risk for the incidence of a disease, particularly a chronic disease or infectious disease that confers immunity, is not easy to discover in populations. Sometimes incidence numbers are used; sometimes the assumption is made that the prevalence of the disease with the prevalence of immunity to the disease is fairly similar and the total population is used.

Question 17 - What are some of the problems with either the incidence number or the use of the total population instead of the population at risk?

Question 18 - Why are disease reports in registries less satisfactory for measurement of prevalence?

Question 19 - What are the country-specific crude rates for males? For females? Which country appears to have the more severe problem?

Question 20 - Now compare the age-specific rates, for each sex, between countries. Do these rates give the same picture as the rates for all ages? How might you explain the differences? (You may assume that the rates have been calculated correctly.) Which picture is correct?

Question 21 - Sketch a graph of the age-specific rates for males in each country.

Attachment:- Assignment File.rar