Epi

Endemic means that a disease: a. Occurs clearly in excess of normal expectancy b. Is habitually present in human populations c. Affects a large number of countries simultaneously d. Exhibits a seasonal pattern e. Is prevalent among animals

The best answer is b. The term endemic is defined in the text as, "the habitual presence of a disease within a given geographical area." Therefore, the levels of an endemic disease may vary over time but the disease remains present in a population. Answer a is incorrect because this statement describes an epidemic. Answer c is incorrect since this statement describes a pandemic disease when the disease levels are greater than expected, and is not a necessary condition for an endemic disease. Answer d may be a characteristic of specific endemic diseases; however, it is not true for all endemic diseases. Finally, answer e describes a zoonotic disease.

Which of the following is characteristic of a single-exposure, common-vehicle outbreak? a.Frequent secondary cases b.Increasing severity with increasing age c.Explosive d.Cases include both people who have been exposed and those who were not exposed e.All of the above

The best answer is c. There are three characteristic features of a single-exposure common vehicle outbreak which include: (1) it is explosive (since all cases are exposed at the same point in time, there is a sudden and rapid increase in the number of cases in a population); (2) the cases are limited to people who share the common exposure; and (3) cases rarely occur in persons who acquire the disease from a primary case. Answer b is incorrect since increasing severity with increasing age is a common characteristic of many infectious disease outbreaks and not just single-exposure common- vehicle. Answer c is incorrect because there are rarely secondary cases in a single exposure outbreak. Answer d is not correct since cases only include those who are exposed to the infectious agent. Finally, answer e is incorrect since only one statement is applicable.

In the study of an outbreak of an infectious disease, plotting an epidemic curve is useful because: a. It helps to determine what type of outbreak (e.g., single-source, person-to-person) has occurred b.It shows whether herd immunity has occurred c.It helps to determine the median incubation period d.a and c e.a, b, and c

The best answer is d. An epidemic curve is the distribution of the times of onset of a disease. Plotting an epidemic curve helps to determine the type of outbreak that has occurred, for example, a single exposure outbreak may be unimodal with a long right tail whereas a multiple exposure outbreak may be bimodal (answer a). Plotting the epidemic curve also allows for the estimation of the median incubation period (answer c). Answer b is incorrect since an epidemic curve is not useful for showing whether herd immunity occurred since those who do not develop the disease, i.e., the immune, are not represented in the epidemic curve.

At an initial examination in Oxford, Mass., migraine headache was found in 5 of 1,000 men aged 30 to 35 years and in 10 of 1,000 women aged 30 to 35 years. The inference that women have a two times greater risk of developing migraine headache than do men in this age group is: a. Correct b.Incorrect, because a ratio has been used to compare male and female rates c.Incorrect, because of failure to recognize the effect of age in the two groups d.Incorrect, because no data for a comparison or control group are given e. Incorrect, because of failure to distinguish between incidence and prevalence

The best answer is e. The inference is incorrect because a comparison of risk involves comparing measures of disease incidence. The example describes the prevalence of migraine headache in men and women of the same age group. Prevalence represents all cases of a disease in a population at the time of examination; therefore, it is influenced by the duration of time that individuals have a disease. Incidence is the total number of cases of a disease that develop during a specified time interval divided by the total number of persons at risk for the disease for the same time period. Since incidence measures the transition from nondiseased to diseased status, it is considered a measure of risk. Statement a is wrong as the inference is incorrect. Statement b is wrong because two prevalence ratios are presented; however, they do not describe risk. Statement c is wrong because the comparison is restricted to a single age group. Statement d is wrong because data are given to compare men and women; however, additional information is needed to describe risk.