PUBH 3351 Midterm 1

What is the definition of epidemiology?

The study of the occurrence, distribution, and determinants of health-related states or events in specified populations, and the application of this study to control health problems.

What is the difference between an endemic and an epidemic?

Endemic is the habitual presence of a disease within a given geographic area; epidemic is the occurrence of illness in a community clearly in excess of normal expectancy.

What are the elements of the epidemiologic triad?

Host, Agent, Environment, and Vector.

What mode of transmission is mother-to-child (vertical) transmission?

Direct, person-to-person transmission.

What does the iceberg concept of infectious disease illustrate?

Only symptomatic (clinical) individuals are discernible at the top, while the vast majority of infections are subclinical or inapparent below the surface.

What subcategories make up non-clinical (inapparent) disease?

Preclinical disease, subclinical disease, persistent (chronic) disease, and latent disease.

What is the incubation period?

The time interval from receipt of infection to the onset of clinical illness.

What is herd immunity and what are its key characteristics?

The resistance of a community to an attack by a disease due to a large proportion of immune individuals; agent must be restricted to humans and immunity can be via vaccination or natural infection.

What are the critical components of an informative epidemic curve?

Descriptive title (identifying time frame and geographic location), date of onset/time since exposure, and total number of cases.

What does a unimodal epidemic curve with a single sharp peak indicate?

A single-exposure, point-source common vehicle outbreak.

What is the formula for a food-specific attack rate?

(Number of people who ate a specific food and became ill) / (Total number of people who ate that food).

How do you identify the infective food item in an outbreak investigation?

Calculate food-specific attack rates for those exposed vs. unexposed; the food with the highest attack rate among exposed and largest difference from unexposed is the cause.

What is the incidence rate formula?

(Number of new cases of a disease in a population during a specified period) / (Number of persons at risk of developing the disease during that period).

What is the prevalence rate formula?

(Number of total existing cases of a disease in a population at a specified time) / (Total number of persons in the population at that time).

What is the mathematical relationship between prevalence, incidence, and duration?

Prevalence $\approx$ Incidence $\times$ Duration of disease ($P \approx I \times D$).

In a town of 1,200 people with 91 new cases and 101 total cases, what are the incidence and prevalence?

Incidence = 91/1,200 = 7.5 per 100 population; Prevalence = 101/1,200 = 8.4 per 100 population.

If prevalence and incidence rates are very close in value, what does this indicate about disease duration?

The duration of the disease is short.

In a study tracking 12,327 people where 309 have disease at baseline and 505 develop it during follow-up, what are the baseline prevalence and incidence?

Baseline Prevalence = 309/12,327 = 25.1 per 1,000; Incidence = 505/(12,327 - 309) = 42.0 per 1,000.

What is an advantage of active surveillance over passive surveillance?

It yields more accurate data because trained project staff use a standardized case definition.

What is primary prevention and what is an example?

Interventions to prevent disease onset before it occurs; Example: Influenza vaccination.

What is secondary prevention and what is an example?

Early detection of disease through screening before clinical symptoms appear; Example: Screening for skin cancer.

What is the Crude Mortality Rate formula?

(Total deaths from all causes in a population during a year) / (Mid-year total population).

What is the Cause-Specific Mortality Rate formula?

(Deaths from a specific disease in a population during a year) / (Mid-year total population).

What is the Age-Specific Mortality Rate formula?

(Deaths in a specific age group during a year) / (Mid-year population of that specific age group).

What is the Proportionate Mortality formula?

(Number of deaths from a specific disease) / (Total number of deaths from all causes).

What is the Case-Fatality Rate (CFR) formula?

(Number of deaths from a specific disease) / (Total number of individuals diagnosed with that disease).

In a city of 150,000 with 1,200 total deaths, 125 malaria deaths, and 1,000 malaria cases, what are Crude Mortality and CFR?

Crude Mortality = 1,200/150,000 = 0.80 per 100; Case-Fatality Rate = 125/1,000 = 12.5%.

In a city of 150,000 with 1,200 total deaths and 125 malaria deaths, what are Proportionate Mortality and Cause-Specific Mortality?

Proportionate Mortality = 125/1,200 = 10.4%; Cause-Specific Mortality = 125/150,000 = 0.08 per 100.

Why is age adjustment used when comparing mortality rates between populations?

To eliminate or reduce the confounding effects of differences in population age distributions.

What is the Standardized Mortality Ratio (SMR) formula?

$\text{SMR} = (\text{Observed Deaths} / \text{Expected Deaths}) \times 100$.

How do you interpret an SMR greater than 100% (or greater than 1.0)?

Observed deaths exceed expected deaths, indicating increased risk / health concerns in the study population.

For a disease with high 5-year survival (>80%), how does incidence compare to mortality?

The incidence rate will be much higher than the mortality rate.

For a highly fatal disease with short duration (e.g., pancreatic cancer), how does incidence compare to cause-specific mortality?

The incidence rate will be nearly equal to the cause-specific mortality rate.

If prevalence is 2x higher in women than men but incidence is equal, what explains the difference?

Women have a longer disease duration or a lower case-fatality rate compared to men.

What is Years of Potential Life Lost (YPLL) and what does it measure?

A measure of premature mortality that quantifies years lost when an individual dies before a benchmark age/life expectancy.

How is YPLL calculated for individuals dying below benchmark age?

$\text{YPLL} = \sum (\text{Life Expectancy Benchmark} - \text{Age at Death})$.

Four people die before benchmark age 78 at ages 3, 18, 22, and 25; what is total YPLL?

$\text{YPLL} = (78-3) + (78-18) + (78-22) + (78-25) = 75 + 60 + 56 + 53 = 244 \text{ years}$.

What key measures are used to evaluate prognosis in clinical epidemiology?

Case-fatality rate, 5-year survival, median survival time, relative survival, and Kaplan-Meier observed survival curves.

In a life table survival analysis, what is $I'_x$ (effective number exposed to risk)?

$I'_x = I_x - \frac{1}{2} w_x$, where $I_x$ is alive at start and $w_x$ is withdrew during interval.

What are the core assumptions of survival analyses and life tables?

1. Those who withdraw are similar to those who remain; 2. Survivorship does not change over calendar time; 3. Events and withdrawals occur uniformly within intervals.

On a Kaplan-Meier survival curve, how do you locate median survival time?

Find 50% survival on the y-axis, move horizontally to intersect the survival curve, and read the corresponding time on the x-axis.

Who is known as the father of modern epidemiology and shoe-leather epidemiology?

John Snow (for investigating the 1854 Broad Street cholera outbreak).

Who led the global public health effort to eradicate smallpox?

D.A. Henderson.