Epidemiology Quiz 1 -Chapters 1-3

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.

Rates would increase in women older than 50 years of age but may decrease in younger women as they get older. Women who have had hysterectomies (i.e., removal of the uterus) are no longer at risk for uterine cancer. For women older than 50 years of age, this would increase the age-specific incidence rate as there would be the same number of uterine cancers occurring among fewer women at risk. Further, rates may decrease among younger women who have had hysterectomies as they are no longer at risk for uterine cancer and thus may decrease the number of potential cases occurring in their age group over time.

Which of the following is an advantage of active surveillance?

more accurate due to reduced reporting burden for health care providers

prevalence rate

number of affected persons present in the population at a specified time divided by the number of person in the population-- not a measure of disease risk, measure of disease burden prevalence per 1,000= # cases of disease present in the population at a specified time/# of persons in the population at a specified time

incidence rate

number of new cases of a disease that occur during a specified period of time in a population at risk for developing the disease- measure of disease risk incidence per 1,000=# new cases of disease occurring during a specified time period/# of persons at risk of developing disease during that time period

epidemic

occurrence of illnesses clearly in excess of a normal expectancy

indirect transmission

through a common vehicle (air, water) or through a vector

passive surveillance

usually reported by health care providers; relatively inexpensive (infectious diseases)

pandemic

worldwide epidemic

Which of the food items (or combination of items) is most likely to be the infective item(s)?

Ice cream only Among persons eating ice cream, over 70% developed diarrhea regardless of their pizza consumption (39/52 and 11/15). Among both groups of persons who did not eat ice cream, each attack rate was equal to or less than 35% (14/40 and 9/30).

The ability of a single person to remain free of clinical illness following exposure to an infectious agent is known as:

Immunity Immunity is the capacity of a single individual to avoid disease susceptibility when exposed to an infectious agent. Herd immunity is a population characteristic. For certain diseases, individual immunity can be acquired by vaccination, but this is not true for all infectious diseases.

A disease has an incidence of 10 per 1,000 persons per year, and 80% of those affected will die within 1 year. Prior to the year 2000, only 50% of cases of the disease were detected by physician diagnosis prior to death. In the year 2000, a lab test was developed that identified 90% of cases an average of 6 months prior to symptom onset; however, the prognosis did not improve after diagnosis. Which statement is true concerning the duration of the disease after the development of the lab test?

Mean duration of a case of the disease is longer in 2000 Though the prognosis is similar after the development of the lab test, the duration of new cases identified by the test can be increased by up to 6 months due to earlier detection.

Which of the following statements are true? More than one answer may be correct.

Prevalence rates are useful for public health planning Incidence rates can be used to estimate prevalence when the mean duration of the disease is known

Which of the following is a condition which may occur during the incubation period?

Transmission of infection The incubation period is defined as the interval from receipt of infection to the time of onset of clinical illness. Accordingly, individuals may transmit infectious agents during the incubation period as they show no signs of disease that would enable the isolation of sick individuals by quarantine.

direct transmission

person to person

In the study of an outbreak of an infectious disease, plotting an epidemic curve is useful because:

-It helps to determine what type of outbreak (e.g., single source, person to person) has occurred -It helps to determine the median incubation period

Which of the following reasons can explain why a person who did not consume the infective food item got sick?

-They were directly exposed to persons who did eat the infective food item -Diarrhea is a general symptom consistent with a number of illnesses -There may have been an inaccurate recall of which foods were eaten Without knowledge as to the specific agent in this instance, it is also likely that it can be spread by direct contact with infected persons. Since diarrhea is a general disease symptom, it is possible that several infectious agents may be present at this meal or others eaten during the same time period. Further, information regarding food consumption may have been collected long after the disease episode. This may have led persons to incorrectly remember the foods that they consumed.

A prevalence survey conducted from January 1 through December 31, 2012, identified 1,000 cases of schizophrenia in a city of 2 million persons. The incidence rate of schizophrenia in this population is 5/100,000 persons each year. What percent of the 1,000 cases were newly diagnosed in 2012?

10%

The following table gives the mean annual age-specific mortality rates from measles during the first 25 years of life in successive 5-year periods. You may assume that the population is in a steady state (i.e., migrations out are equal to migrations in). The age-specific mortality rates for the cohort born in 1915-1919 are:

2.4 3.3 2.0 0.6 0.1 This is found by tracking the cohort of children born between 1915 and 1919 by each 5-year age group. For example, this group would be 0 to 4 years of age in 1915 to 1919 with a rate of measles mortality of 2.4. In 1920 to 1924, this group of children would be 5 to 9 years of age and have a rate of measles mortality of 3.3. Continuing in a diagonal manner, the remaining three rates can be found in the table.

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 monthly incidence rate of active cases of influenza for the 3-month period was:

20 per 1,000 population The monthly incidence rate is calculated based on the number of new cases of a disease developing during the 3-month time period. In this example, 2,200 cases of influenza developed among an average population of 36,600 persons at risk during the surveillance period. The incidence rate equals 2,200 divided by 36,600. In order to calculate the average monthly rate, the rate should then be divided by 3. Finally, the monthly rate can be multiplied by 1,000 in order to express it per the responses listed.

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:

20 per 1,000 population The prevalence rate as of April 1, 2005, is equal to the number of active influenza cases reported divided by the number of persons at risk in the population at that time. The best estimate of the population size is that from the February 15 count, less who are no longer at risk as they have already recovered from influenza and have developed immunity. Therefore, prevalence equals 705 cases divided by 36,600 less 1,495 recovered cases. This number can be multiplied by 1,000 in order to estimate a prevalence rate of 20 cases per 1,000 persons.

What is the overall attack rate in persons who did not eat ice cream?

33% The attack rate is the number of persons with diarrhea (14 + 9) divided by the total number of persons who did not eat ice cream (40 + 30).

What is the diarrhea attack rate in persons who ate both ice cream and pizza?

39/52 The attack rate in this example is defined as the number of persons who develop diarrhea divided by the total number of people at risk. In this example, the at-risk group is those who have eaten both ice cream and pizza. Of these 52 persons, 39 developed diarrhea.

In 2001, a state enacted a law that required the use of safety seats for all children under 7 years of age and mandatory seatbelt use for all persons. The table below lists the number of deaths due to motor vehicle accidents (MVAs) and the total population by age in 2000 (before the law) and in 2005 (4 years after the law was enacted). What is the age-specific mortality rate due to MVAs for children ages 0 to 18 years in 2000?

6.1 per 1,000 The rate is found by combining the MVA deaths and total population size for the two age groups under 7 years and 7 to 18 years during the year 2000. This equals (44 + 105) divided by (3,500 + 21,000). Multiplying this rate by 1,000 persons gives the answer indicated.

What is the sore throat attack rate in persons who ate both egg salad and tuna?

60/75

Which of the following statements are true? More than one answer may be correct.

A mortality rate is an example of an incidence rate A mortality rate can approximate an incidence rate under conditions of a high case-fatality rate and a short duration of disease.

An outbreak of gastroenteritis occurred at a boarding school with a student enrollment of 846. Fifty-seven students reported symptoms including vomiting, diarrhea, nausea, and low-grade fever between 10 p.m. on September 24 and 8 p.m. on September 25. The ill students lived in dormitories that housed 723 of the students. The table below provides information on the number of students per type of residence and the number reporting illnesses consistent with the described symptoms and onset time. Which proportion is more informative for the purpose of the outbreak investigation?

Both proportions are useful. Dormitory residents account for over 90% of the cases indicating an outbreak of an infectious agent that was transmitted at the school. Furthermore, over 75% of the cases were boys indicating that the responsible agent was more likely to have been transmitted in the boys' dormitory.

The following table gives the mean annual age-specific mortality rates from measles during the first 25 years of life in successive 5-year periods. You may assume that the population is in a steady state (i.e., migrations out are equal to migrations in). Based on the information above, one may conclude:

Children ages 5 to 9 had the highest rate of death in all periods For each 5-year period, the highest mortality rate is reported among those 5 to 9 years of age. This is seen by comparing the rate for this age group to all other age groups in a row.

The table below describes the number of illnesses and deaths caused by plague in four communities. The case-fatality rate associated with plague is lowest in which community?

Community C The case-fatality rate equals the number of deaths occurring from plague divided by all persons with the plague. In Community C, the CFR is 300 divided by 400, or 60%. This is lower than A (67%), B (75%), and D (77%).

The table below describes the number of illnesses and deaths caused by plague in four communities. The proportionate mortality ratio associated with plague is lowest in which community?

Community D The proportionate mortality rate equals the number of deaths occurring from plague divided by all persons with the plague. In Community D, the PMR is 500 divided by 5000, or 10%. This is lower than A (50%), B (75%), and D (38%).

Chicken pox is a highly communicable disease. It may be transmitted by direct contact with a person infected with the varicella-zoster virus (VZV). The typical incubation time is between 10 to 20 days. A boy started school 2 weeks after showing symptoms of chicken pox including mild fever, skin rash, and fluid-filled blisters. One month after the boy returned to school, none of his classmates had been infected by VZV. The main reason was:

Contact was after infectious period The disease is spread by contact with an infected individual who can transmit the agent (VZV) to immunologically naive persons during the incubation period and for several days after onset of clinical illness. Since the boy started school 14 days after showing signs consistent with chicken pox, it is most likely that he was no longer infectious.

In 2001, a state enacted a law that required the use of safety seats for all children under 7 years of age and mandatory seatbelt use for all persons. The table below lists the number of deaths due to motor vehicle accidents (MVAs) and the total population by age in 2000 (before the law) and in 2005 (4 years after the law was enacted). Based on the information in the table, it was reported that there was an increased risk of death due to MVAs in the state after the law was passed. These conclusions are:

Correct, because both the total and the age-adjusted mortality rates are higher in 2005 than in 2000 The overall crude (unadjusted) mortality rate is 2.6 per 1,000 persons in 2005. This is found by dividing 640 deaths by a population of 240,000 persons. This rate is then multiplied by 1,000. The overall adjusted mortality rate is 2.3 per 1,000 persons as calculated in question 34. Both of these rates are higher than the overall crude mortality rate of 2.0 per 1,000 persons for the year 2000.

According to the results shown in the preceding tables, which of the following food items (or combination of food items) is most likely to be infective?

Egg salad only

Which of the following is characteristic of a single-exposure, common-vehicle outbreak?

Explosive

An outbreak of gastroenteritis occurred at a boarding school with a student enrollment of 846. Fifty-seven students reported symptoms including vomiting, diarrhea, nausea, and low-grade fever between 10 p.m. on September 24 and 8 p.m. on September 25. The ill students lived in dormitories that housed 723 of the students. The table below provides information on the number of students per type of residence and the number reporting illnesses consistent with the described symptoms and onset time. Calculate the attack rates for boys and girls separately.

For boys, the attack rate includes all cases (40 + 3) divided by the total number of students who are boys (380 + 46). The attack rate is 10.1%. For girls, the attack rate includes all cases (12 + 2) divided by the total number of students who are girls (343 + 77). The attack rate is 3.3%.

A disease has an incidence of 10 per 1,000 persons per year, and 80% of those affected will die within 1 year. Prior to the year 2000, only 50% of cases of the disease were detected by physician diagnosis prior to death. In the year 2000, a lab test was developed that identified 90% of cases an average of 6 months prior to symptom onset; however, the prognosis did not improve after diagnosis. Comparing the epidemiology of the disease prior to 2000 with the epidemiology of the disease after the development of the lab test, which statement is true concerning the disease in 2000?

Incidence is higher and prevalence is higher than in 1999 With increased ability to detect cases of the disease at earlier times, both the number of incidence and prevalent cases will increase through better detection.

A study found that adults older than age 50 had a higher prevalence of pneumonia than those who were younger than age 50. Which of the following is consistent with this finding?

Incidence rates do not vary by age, but older adults have pneumonia for a longer duration compared to younger adults For prevalence to be higher among older adults, either incidence or duration of pneumonia must be increased in this age group.

For a disease such as liver cancer, which is highly fatal and of short duration, which of the following statements is true? Choose the best answer.

Incidence rates will be equal to mortality rates Since the 5-year survival rate for liver cancer is 4%, most incident cases of liver cancer will result in a premature mortality. In this case, the mortality and incidence rates will be approximately equal.

For colorectal cancer diagnosed at an early stage, the disease can have 5-year survival rates of greater than 80%. Which answer best describes early stage colorectal cancer?

Incidence rates will be much higher than mortality rates For diseases with a long duration as indicated by high 5-year survival rates for early stage colorectal cancer, the incidence will be much higher than the mortality rate since more persons are being diagnosed with the disease than are dying of it.

Among those who are 25 years of age, those who have been driving less than 5 years had 13,700 motor vehicle accidents in 1 year, while those who had been driving for more than 5 years had 21,680 motor vehicle accidents during the same time period. It was concluded from these data that 25-year-olds with more driving experience have increased accidents compared to those who started driving later. This conclusion is:

Incorrect because rates are not reported The information provided only enumerates motor vehicle accidents in two groups. In order to fully compare these counts, information is needed on the denominator, i.e., the number of persons driving in each group, so that rates can be calculated.

At an initial examination in Oxford, Mass., migraine headache was found in 5 of 1,000 men aged 30-35 years and in 10 of 1,000 women aged 30-35 years. The interference that women have a two times greater risk of developing migraine headache than do men in this age group is:

Incorrect, because of failure to distinguish between incidence and prevalence

Endemic means that a disease:

Is habitually present in human populations

A survey was conducted among the non-hospitalized adult population of the United States during 2008-2011. The results from this survey are shown below. The researchers state that there was an age-related increase in the risk of hypertension in this population. You conclude that the researcher's interpretation:

Is incorrect because prevalence is used

A survey was conducted among 1,000 randomly sampled adult males in the United States in 2005. The results from this survey are shown below. The researchers stated that there was a doubling of risk of hypertension in each age group younger than 60 years of age. You conclude that the researchers' interpretation:

Is incorrect because prevalence rates are estimated The survey reports the disease status of a population at a specific point in time. In this case, a random sample of adult males in 2005 provides a reliable estimate of the prevalence of hypertension. Since there is no information on duration of hypertension in these men, incidence cannot be calculated. Therefore, the researchers are not able to make a statement concerning risk of hypertension in the population.

Which of the following is an advantage of active surveillance?

More accurate due to reduced reporting burden for health care providers Active surveillance entails a concerted effort to collect information about disease occurrence. It typically involves dedicated staff members who have been specifically directed to contact physicians and hospitals in order to collect reports of disease cases in a specified population. This activity requires a large amount of staff and resources in order to accomplish its goals.

A prevalence survey conducted from January 1 through December 31, 2003 identified 580 new cases of tuberculosis in a city of 2 million persons. The incidence rate of tuberculosis in this population has historically been 1 per 4,000 persons each year. What is the incident rate of tuberculosis per 100,000 persons in 2003?

The answer is 29 new cases of tuberculosis per 100,000 persons. This is found by dividing the new cases of tuberculosis by the total population at risk (580/2,000,000) and multiplying this rate by 100,000 to standardize the rate.

In a coastal area of a country in which a tsunami struck, there were 100,000 deaths in a population of 2.4 million for the year ending December 31, 2005. What was the all-cause crude mortality rate per 1,000 persons during 2005?

The answer is 41.7 per 1,000 persons. The rate is calculated by dividing 100,000 deaths by the population of 2,400,000 persons. To express as a rate per 1,000 persons, the rate is multiplied by 1,000.

In an industrialized nation, there were 192 deaths due to lung diseases in miners ages 20 to 64 years. The expected number of deaths in this occupational group, based on age-specific death rates for lung diseases in all males ages 20 to 64 years, was 238 during 1990. What was the standardized mortality ratio (SMR) for lung diseases in miners?

The answer is 81. The ratio is calculated by dividing 192 observed deaths by the 238 expected deaths for this age group. To express it as an SMR, the ratio is often multiplied by 100.

An outbreak of gastroenteritis occurred at a boarding school with a student enrollment of 846. Fifty-seven students reported symptoms including vomiting, diarrhea, nausea, and low-grade fever between 10 p.m. on September 24 and 8 p.m. on September 25. The ill students lived in dormitories that housed 723 of the students. The table below provides information on the number of students per type of residence and the number reporting illnesses consistent with the described symptoms and onset time. Calculate the attack rate among all students at the boarding school.

The answer is found by dividing the total number of cases (57) by the total number of students (846). This equals 6.7%. The answer is found by dividing the total number of cases (57) by the total number of students (846). This equals 6.7%.

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. What can be inferred about influenza cases occurring in the city?

The average duration of influenza is approximately 1 month Since the average monthly incidence rate is 20 per 1,000 and the prevalence rate is also 20 per 1,000, then the duration of disease must equal 1 month.

Which of the following characteristics indicate that mortality rates provide a reliable estimate of disease incidence? More than one answer may be correct.

The case-fatality rate is high The duration of disease is short

The prevalence rate of a disease is two times greater in women than in men, but the incidence rates are the same in men and women. Which of the following statements may explain this situation?

The case-fatality rate is lower for women Since men and women develop the disease at the same rate, the survival rate in women must be increased in order to increase duration and prevalence. A low case-fatality rate would contribute to an increased duration of the disease.

In 2001, a state enacted a law that required the use of safety seats for all children under 7 years of age and mandatory seatbelt use for all persons. The table below lists the number of deaths due to motor vehicle accidents (MVAs) and the total population by age in 2000 (before the law) and in 2005 (4 years after the law was enacted). Using the pooled total of the 2000 and 2005 populations as the standard rate, calculate the age-adjusted mortality rate due to MVAs in 2005.

The correct answer is 2.3 MVA deaths per 1,000 persons. The key to calculating the age-adjusted rate is to pool the observed numbers for both time periods and to calculate the expected numbers of deaths in the 2005 population assuming that a common rate applied to the population. For example, for those under 7 years, the pooled rate equals (44 + 20) divided by (3,500 + 4,000). The pooled rate for this group is 8.5 per 1,000 persons. When this rate is multiplied by the 4,000 children under 7 years of age in 2005, the expected number of deaths is 34.13. Performing the same calculation for each age group results in 111.7 deaths in those 7 to 18 years of age, 175.8 deaths in those 19 to 49 years, and 237.35 deaths for those 50 years or more. The total number of deaths expected in 2005 based on this pooled rate is 558.98. Therefore, the age-adjusted overall rate for 2005 is 558.98 deaths divided by 240,000 persons.

The incidence and prevalence rates of a chronic childhood illness for a specific community are given below. Based on the data, which of the following interpretations best describes disease X?

The duration of disease is becoming shorter. Prevalence and incidence are related by the duration of disease. If incidence is increasing over time, then duration of illness has to decrease in order to keep the prevalence rate constant. This may occur through better treatments to cure disease or through higher case-fatality rates as a disease becomes more lethal. Since incidence is increasing over time, it is evident that risk is also increasing and that prevention efforts are not successful.

Which of the following is characteristic of a single-exposure, common-vehicle outbreak?

The epidemic curve has a normal distribution when plotted against the logarithm of time Single-exposure, common-vehicle outbreaks involve a sudden, rapid increase in cases of disease that are limited to persons who share a common exposure. Additionally, few secondary cases develop among persons exposed to primary cases. A histogram of the outbreak can plot the number of cases by time of disease onset. In single-exposure, common-vehicle outbreaks, a log transformation of the time of disease onset will often take on the characteristic shape of a normal distribution (i.e., a bell curve) with the median incubation time found at the peak of the curve.

A group of researchers are interested in conducting a clinical trial to determine whether a new cholesterol-lowering agent was useful in preventing coronary heart disease (CHD). They identified 12,327 potential participants for the trial. At the initial clinical exam, 309 were discovered to have CHD. The remaining subjects entered the trial and were divided equally into the treatment and placebo groups. Of those in the treatment group, 505 developed CHD after 5 years of follow-up while 477 developed CHD during the same period in the placebo group. What was the incidence of CHD during the 5-year study?

The incidence rate reflects the number of new cases developing in the population at risk. Since prevalent CHD cases were excluded from the study, the population at risk was 12,018 (12,327 persons less 309 cases of CHD). During the 5-year study period, 982 incident cases of CHD developed. This equals an incidence rate of 81.7 cases of CHD per 1,000 persons.

A disease has an incidence of 10 per 1,000 persons per year, and 80% of those affected will die within 1 year. Prior to the year 2000, only 50% of cases of the disease were detected by physician diagnosis prior to death. In the year 2000, a lab test was developed that identified 90% of cases an average of 6 months prior to symptom onset; however, the prognosis did not improve after diagnosis. Which statement is true concerning the disease-specific mortality rate after the development of the lab test?

The mortality rate for the disease is the same in 2000 With the implementation of the lab test, the increase in early detection of cases will increase incidence, duration, and prevalence; however, since the prognosis is still the same, at least 80% of patients will die during the year 2000. This should result in a similar mortality rate as the previous year given no change in transmission, prevention, or medical care of the disease.

Which of the following are examples of a population prevalence rate?

The number of persons with hypertension per 100,000 population Prevalence is the number of affected persons in a specified population size at a given time. Only answer (b) fits this definition. Example (a) is more consistent with an incident rate while answer (c) is a selected group of persons who may not be representative of a general population.

A group of researchers are interested in conducting a clinical trial to determine whether a new cholesterol-lowering agent was useful in preventing coronary heart disease (CHD). They identified 12,327 potential participants for the trial. At the initial clinical exam, 309 were discovered to have CHD. The remaining subjects entered the trial and were divided equally into the treatment and placebo groups. Of those in the treatment group, 505 developed CHD after 5 years of follow-up while 477 developed CHD during the same period in the placebo group. What was the prevalence of CHD at the initial exam?

The prevalence of CHD at the initial exam was 309 cases of CHD divided by 12,327 participants. This equals a prevalence of 25.1 cases of CHD per 1,000 persons.

AR

attack rates= # of people at risk in whom an illness develops/total # of people at risk

An outbreak of gastroenteritis occurred at a boarding school with a student enrollment of 846. Fifty-seven students reported symptoms including vomiting, diarrhea, nausea, and low-grade fever between 10 p.m. on September 24 and 8 p.m. on September 25. The ill students lived in dormitories that housed 723 of the students. The table below provides information on the number of students per type of residence and the number reporting illnesses consistent with the described symptoms and onset time. What is the proportion of total cases occurring in boys?

The proportion of cases occurring in boys is equal to the number of cases in boys divided by the total number of cases (43/57). This equals 75.4%.

An outbreak of gastroenteritis occurred at a boarding school with a student enrollment of 846. Fifty-seven students reported symptoms including vomiting, diarrhea, nausea, and low-grade fever between 10 p.m. on September 24 and 8 p.m. on September 25. The ill students lived in dormitories that housed 723 of the students. The table below provides information on the number of students per type of residence and the number reporting illnesses consistent with the described symptoms and onset time. What is the proportion of total cases occurring in students who live in dormitories?

The proportion of cases occurring in dormitory residents is equal to the number of cases in residents divided by the total number of cases (52/57). This equals 91.2%.

What would be the effect on age-specific incidence rates of uterine cancer if women with hysterectomies were excluded from the denominator of the calculations, assuming that there are some women in each age group who have had hysterectomies?

The rates would tend to decrease

A prevalence survey conducted from January 1 through December 31, 2003 identified 580 new cases of tuberculosis in a city of 2 million persons. The incidence rate of tuberculosis in this population has historically been 1 per 4,000 persons each year. Has the risk of tuberculosis increased or decreased during 2003?

The risk of tuberculosis has increased over the historic incident rate. This comparison can be made by standardizing the historic rate to a rate per 100,000 persons. To do this, multiply the numerator and denominator by 25.

incubation period

interval from the time of infection to the time of clinical illness

Secondary prevention

early detection of existing disease to reduce severity and complications

endemic

habitual presence of a disease within a given geographical area

point prevalence

prevalence at a specific point in time "do you currently have asthma?"

period prevalence

prevalence over a specified period of time "have you had asthma in the last x years?"

two most common rates of epidemiology

prevalence, incidence

prevalence equation

prevalence~incidence x duration

Primary prevention

preventing the initial development of a disease

Tertiary prevention

reducing the impact of the disease

herd immunity

resistance of a group of individuals to developing the disease due to a large percent of the group being immune

active surveillance

staff are recruited to carry out the surveillance ($$); conducts surveys; identify new cases

epidemiology

study of how disease is distributed in human populations and the factors that influence or determine this distribution

rate

tells how fast the disease is occurring within a population

proportion

tells the fraction of the population that is affected