prevention and control of two persistent illnesses – HIV/AIDS and Tuberculosis

prevention and control of two persistent illnesses – HIV/AIDS and Tuberculosis

• In light of Center for Disease Control and Prevention recommendations, is enough being done to control the incidence of these illnesses?
• How can a Community Health Nurse exercise the role of Educator?
• Include theory from your text and any lecture material.
• The Montgomery County, Maryland website should also be accessed and investigated.
CDC Link:

Book used chapter 14: Stanhope, Marcia and Lancaster, Jeanette (2012) Public Health Nursing, Population-Centered Heath Care in the Community, 8th ed., Maryland Heights, MO; Elsevier Mosby


Epidemiology is often considered to be the “soul” of Public and Community Health Practice. It is the core science of Public Health, having the overall goal of optimal health for the entire community. It has been the foundation used for virtually every treatment and control measure known when trying to eradicate communicable diseases. It is used to predict “risk” in populations and it is used to keep a watch on the goings on in the environment, from polluted waters to sentinel diseases which may mark the onset of a bioterrorism event or a brand new infectious disease

Epidemiology (Epi) defined is the study and investigative process of the distribution and determinants (trends) of events in specific populations. The application of this study is the control measure(s) which are put into place in order to stop disease form progressing.
Epi. doesn’t just refer to infectious diseases. Rather, it now encompasses work done with chronic illness, mental illness, accidents, occupational and environmental exposures and substance abuse, to name a few.
Epi. relies on statistical evidence to determine the rate of disease spread and the proportion of people in the community who are at risk or who are affected. For example, epidemiology study of rates and proportions has allowed us to identify that lung cancer now is the leading cause of death in women surpassing breast cancer. We know that smoking rates among women have increased and we know that media and advertising now target women. Both are risk factors and both involve a proportion of our population. When we know these trends, it helps to then focus on prevention and control.

The distribution of the disease event is the particular pattern….the who, what, when, where and why. This is called descriptive epidemiology because it describes the occurrence of disease in relation to people, place and time.
The determinants are those factors that determine or influence the pattern (distribution.) Examples are: length of exposure to an infectious germ, characteristics, how the germ is spread, causes, why certain people are susceptible, etc. This is called analytical epidemiology, which is the understanding of the etiology of a disease.

The FIRST step in any epidemiological investigation is to define whether or not there is a CASE. This calls for precise diagnostic criteria. The reason this is important is shown by this example. Suppose you had a doctor in the Emergency Room who suspects a case of Anthrax. He calls the local health department to report that suspicion. It would not be appropriate to initiate an emergency public health response based on the suspicion.
Instead, epidemiological investigation confirms whether or not this is an actual case. Only then does the public health emergency response get initiated. By calling it a “case” too early, it can spur panic in the population and inappropriate, very expensive action on the part of responding agencies such as local health departments.

Clinical medicine focuses on diagnosis and treatment, usually of an individual patient. Epi. On the other hand, focuses on the health of the population, by understanding what is going on in the community through watching determinants of disease and the pattern. Once that is understood, epidemiologists recommend interventions that improve the health and prevent the recurrence of the disease.

Any description of the disease pattern (the who, what, when, where, and why) should take into account the size of the population and the risk for the disease. People differ in their risk for disease. One focus of epidemiology is to figure out how they differ and why? We don’t look solely look at numbers of cases. We also look at the number of people at risk for a given time. Think of the number of cases as the numerator, and the number of people at risk, the denominator. 50 cases of influenza in a population of 250 (50/250) would probably be considered as an epidemic. But 50 cases in a population of 250,000 (50/250,000) would not.

The above are proportions which epidemiologists rely upon constantly to determine how serious the disease is affecting the health of any given population. A proportion is a type of ratio in which the denominator includes the numerator. Taking the above example, 50/250 = .20 or 20% of a population is affected. Proportions range from 0-1 (in this case .20) and are often multiplied by 100 and expressed as a percent (20%) If the proportion is very small, public health statisticians use a larger multiplier (1000 or 100,000) to avoid small fractions. Again, using the example, 50/250 = .20 or 20 per 100 people.
Another word to remember is RATE. Rate is the measure of frequency of a health event in a defined population in a specified period of time. A rate is a ratio also, but it is not a proportion, because the denominator is a function of BOTH the population size and the dimensions of time. The numerator is the # of events (or cases.) A proportion can be 0-1, but a rate, depending upon time and frequency, can be greater than 1. Another way of thinking about rate is to substitute the word “speed.” (Think of miles per hour, or rate over time.) Rate is a measurement of how rapidly the disease is developing in the community. Rates deal with change over time.

RISK is the probability that an event will occur within a period of time. Susceptibility to disease varies from one group to another. A high risk population (ex. IV drug users) has certain characteristics (behavior) which make the probability, or risk, go up.

A population at risk, then, is the number of people for whom there is some finite probability of that event, or getting the disease.
Example: No risk = population of men developing ovarian cancer; low risk = population of men developing breast cancer; high risk = population of substance abusers who are IV drug users, developing HIV infection. Unknown risk =population of women unaware that their male sexual partners are not monogamous.
Incidence is the number of new cases in a population at risk during a specified time. Incidence is expressed as a rate because it quantifies how rapidly the disease is developing in a population. If today we have one new case of bacterial meningitis in a college dorm of 100, and tomorrow we have 40 cases in the same dorm, (1/100 vs. 40/100) we can say the rate is both high and rapidly progressing. The IR would be # of new cases (40) divided by the population at risk (100) times 100 or 1000, (the multiplier.) So an IR is expressed as “40 cases per 100 (or 1,000, or 100,000) population.”

Prevalence is a measure of existing disease in a population at a particular time. It takes into account old and new cases. It is expressed as a ratio or rate, too. (Number of existing cases/number of the current population at risk.) Prevalence is not an accurate measure of risk because it takes into account old, existing cases. A disease with a long course and lower number of fatalities (say, tuberculosis) will have a higher prevalence than a rapidly fatal disease (say, Ebola Virus) but each may have the same rate of new cases!

A mortality rate is the number of deaths/population total X 1000 or 100,000. Mortality rates are informative for fatal diseases but do not provide a direction about the prevention or population at risk. Why? Because everyone is at risk for dying! Also, people may die from a different cause other than the underlying disease. (Death certificates often reflect this.) But mortality rates do reflect serious health problems and possible changing patterns of disease.

Attack rate.
Attack rate is the number of people who develop disease/the number of people who are exposed to the disease. The key is that attack rate is linked to exposure. For example, the proportion of people becoming ill after eating a specific food item. (no. of people who develop disease/total number of people who were at risk or those who ate the food.)

Case Fatality Rate.
This is defined as the proportion of people diagnosed with a particular disease that die within a certain period of time. Ex: The proportion of people with breast cancer who die within 5 years. (You will see CFR quoted throughout medical and nursing literature.) Related to this is the Survival Ratewhich is defined as the proportion of people diagnosed with a disease who actually survive it. Most people want to know how long they have to live once diagnosed. This is another way of defining probability of survival. SR is (1) minus the CFR. If the 5 year CFR for lung cancer is 86%, then the SR is 1 – .86, or .14 (14%)

YOU ARE THE NURSE EPIDEMIOLOGIST. Review the next two slides and answer the questions.

An epidemic is when the RATE of disease exceeds the usual levels. There is no specific threshold that indicates that an epidemic exists. In fact, one case of a deadly disease that has a high fatality rate and is thought to be eradicated, Smallpox, would be considered to be an outbreak and an epidemic in the strictest of terms. Conversely 10 new cases of CVD would NOT be considered an epidemic because the disease occurs naturally in high proportions.

In other lectures, there has been reference to the Infant Mortality Rate. Thinking again of numerator and denominator, Infant Mortality is the number of infant (0-1 y.o.) deaths/number of live births in the population over the period of one year.
(# of infant deaths/# live births X 1000 population) These rates are used to compare community to community and country to country. IM is used globally to indicate overall health and availability of health services in a particular country. African American women suffer an infant mortality rate that is twice as high as Caucasian women. That is used to define health disparities and gives clear focus as to where Public Health activities should take place. Nurses are key members in local fetal and infant mortality review boards (FIMR) which examine these rates and the trends of the rates, causes of deaths, risk factors, and quality of care. Prevention measures are then developed following this analysis.

Epidemiology is basically a study of three factors and their relationship to each other, known as the Epidemiology Triangle. Those factors are agent, host andenvironment and are key elements to disease causation. Their interaction determines the development and cessation of communicable diseases and they form the “web of causality” which influences the risk for disease.
Agent – that which causes disease, the bug or germ, also chemical, radiation, etc.
Host – the person susceptible for getting the disease. The host can be susceptible because of genetic factors, factors that cannot change, such as age and sex, acquired characteristics such as immune status and lifestyle/behaviors.
Environment – the world and surroundings that sustain the host.

The relationship between all three defines the disease and the disease process.
Changing any one of these factors can change the others.

The terms infectious disease and communicable disease are, for our purposes defined as one. (Even though not all infectious diseases are transmitted person to person, the definition of communicable.)
Successful transmission of a CD (Communicable Disease) depends on the successful interaction of the pieces of the triangle. You won’t have disease if you don’t have a susceptible host. You won’t have disease if the agent can’t live in the environment, and so on.

Agents are bacteria, fungi, viruses, and parasites. All of them differ in their ability to cause disease. All of them differ in their severity of disease. Exposure to agents does not always lead to infection and infection does not always lead to disease! (ex. People live with the AIDS virus sometimes many years before exhibiting symptoms of the disease.)
Infection depends on the dose of the agent, the ability of the agent to enter the host and multiply, and the ability of the host to combat it. Disease is an outcome of infection.


Keeping in mind the epidemiological triangle and the web of causality or factors that interact that can cause disease, as well as what PH professionals can do to prevent disease, we need to consider the importance of screening. Screening is a key secondary prevention effort. It involves testing a group of people who are at risk for a certain condition or disease but who are currently asymptomatic. The goal is early detection and treatment when these result in a more favorable prognosis. (ex. – colonoscopy) From a PH perspective the goal is to sort out who probably have disease vs. those who probably don’t, to detect cases early, and to begin population-based prevention and control programs. A screening test is not diagnostic! Effective screening must have referral mechanisms built in for further diagnostic work and evaluation to determine the presence of disease and need for treatment. Page 268 has the characteristics of a successful screening program. (to name a couple: they have to have few, if any, side effects, they have to be capable of reaching large numbers of people.) Screening tests have to pass validity (accuracy) and reliability (precise) measures. Validity is measured by sensitivity and specificity. Sensitivity quantifies how accurately the test identifies those with disease. High sensitivity is needed when early treatment is important and when identifying cases is important. The goal is to get true positives!
Specificity indicates how accurately the test identifies those without the disease (the true negatives.)
Reliability (or precision) involves consistency, repeatability, and accuracy of the screening test. Is it really measuring what we think the test is measuring? How exact is it? There are 3 major sources of error that can affect reliability of screens:
1) Variation in what is being measured. BP, for example, can change with the introduction of multiple factors. 2) tester or observer variation and 3) mechanical inconsistencies (a non-working BP cuff!)

Some other terms to remember:
Incubation period – is a time interval. It is the time between the invasion of the agent upon the host and the time of the first clinical sign/symptom. Depending upon the agent, the first signs can appear immediately (certain toxins) or years later (HIV).
The agent’s communicable period is also a time interval. That is the time during which the agent is able to transfer from one infected person to another non-infected person. The Flu, for example is communicable (in other words, you can catch it from another person) during the period of up to 3-5 days after onset of symptoms.

If a disease is endemic to the area, it means that it is already present and known. It has a usual occurrence at a low to moderate level. It establishes the baseline for the definition of an epidemic when the rate of disease exceeds the endemic or usual levels. A newly identified epidemic has been cited by the CDC in this country. Does anyone know what it is? It is obesityObesity was endemic, already present and known. But now the rate of obesity exceeds what would be considered to be “normal” rates.
Every Fall/Winter the United States experiences an endemic Flu bug. A pandemic (a topic which we’ll discuss along with Emergency Preparedness) is a worldwide epidemic which occurs in large populations.) Officials are afraid that the Avian Flu, or H5N1 will soon become a Pandemic.

Disease Surveillance is the process of gathering, analyzing and interpreting data. Who got the disease, when did they get it, what is the cause, where did they get it….then…..the why did they get it? Once all those questions are answered epidemiologists can then make recommendations about the control of the disease. Nurses play an integral part in all steps of the surveillance process: Investigating patient contacts, sources of illness, testing, collecting information, reporting on the data, and assisting with control measures. Active surveillance involves the ongoing search for new cases of disease. Many active surveillances involve “point epidemics.” (A pronounced clustering of cases from a common source within a very short amount of time.) .
These are important for infectious diseases and toxic exposures in the community. A point epidemic plots new cases against a time interval and can show when peaks of the disease are occurring. These peaks indicate the response of a population to a common source of infection or contamination to which they all were exposed. Knowledge of the incubation period of that disease can help determine the time of exposure. This is especially helpful when working a food-borne outbreak. Nurses should be alert to sudden increases in the number of cases they see in an ER, chart the point epidemic, determine the probability of time of exposure and then can isolate the source of the agent. Surveillance helps PH officials identify trends or unusual occurrences, disease patterns and to set priorities for use of resources to prevent and control them

Each state requires that certain diseases be reportable. That is, law requires medical providers, veterinarians, and laboratories to report known cases or agents to the local health department, who in turn reports it to the State, who in turn reports it to the CDC. This is called passive surveillance. See a list of nationally notifiable illnesses on pg. 537-538. These are called “reportable” because they are diseases of special concern if they get out in the community on a wide spread basis. They could be highly fatal infectious diseases, or those which cause widespread infection because they are easily transmissible from person to person.
Before 1990 state and local HD’s used many different criteria for identifying cases of reportable diseases. Using these different criteria made the data less useful when trying to determine case counts, trends, and so on. Some diseases went under or over reported as a result. In 1990 the CDC and the Council of State and Territorial Epidemiologists created the first standard case definitions for the U.S. These case definitions make it possible for reporting and monitoring of diseases in a uniform, standardized way. Case definitions include clinical symptoms, lab values, and epidemiological data such as exposure to an agent.
Each disease has its own criteria based on what is known about the disease. Cases can be classified as suspected, probable, or confirmed. Some diseases REQUIRE that labs confirm even with clinical symptoms present. Other diseases don’t have lab tests yet available to confirm them. Case definition is not the only criterion for taking PH action against the disease. Action to control the disease should take place as soon as the probability is identified. For instance, if a PH dept. became aware of a toxic exposure, the department may recommend evacuation (the action) before a case definition is obtained. Any unusual increase in disease incidence or events in the community should be investigated to:
Control and prevent disease and death
Identify factors responsible
Implement prevention and control efforts
The investigative process in determining whether or not there is an outbreak of something has steps to follow: (slide)
In short, diagnosis must be verified, a case definition is used to help identify the magnitude of the problem, comparison data is used with baseline data, determination of whether or not outside help is needed (like the CDC) determine whether or not it is a reportable illness, develop a hypothesis about the determinants of the disease, implement control measures (to break the cycle of disease!), communicate findings, and follow up on cases.