Speaking Notes

PADM 5324

August 25, 20009

Dr. Neubauer

CHAPTER 2

Focus of medicine -- patient has X. What can be done to help the patient get over or cope with having X?

Focus of public health and epidemiology -- some people have X. Are we sure that it is really X? What steps can be taken to prevent others from getting X? By what VECTOR is X transmitted? What is the likely trajectory of X in the population?

Both medicine and public health share the desire to PREVENT disease. Those in medical practice are more likely to focus on what INDIVIDUALS can do to protect themselves. Those in public health are more likely to focus on prevention in the AGGREGRATE. Generally, these two interests work together.

Sometimes, they may not. An example is the level of prescription of ANTIBIOTICS. The liberal use of antibiotics by individuals can result in a situation in which bacteria adapts into highly resistant strains, which can put the public at a higher level of risk than would otherwise be the case. In other words, there can be a NEGATIVE EXTERNALITY associated with prescriptions of antibiotics for individuals.

It can also work the other way around. While vaccines can carry some risk for individuals there can be a POSITIVE EXTERNALITY associated with immunization. If about 80% of the population receives a vaccine it may be unlikely that the disease will attack the 20%, depending upon the VECTOR of transmission and other aspects of the disease itself.

There are multiple independent variables related to the prevalence of a disease in a population and the likely hood that it will become manifest in an individual.

genetic factors of individuals and groups

demographics regarding individuals and groups

environmental factors

the vector or vectors (modes of transmission)

the probability that exposure will lead to contagion

the duration of time that a person with the disease is contagious

the practical effectiveness of isolation and medical quarantine

the rate at which the disease kills hosts and thereby limits its spread

the behaviors of people as related to potential transmission of the disease

the presence of (partial) immunity within the population

MAJOR PROBLEMS

• something with a very efficient vector
• something for which a population has no natural immunity or vaccine
• something that people who do not have symptoms carry for a long time
• something that is actively evolving in unpredictable ways
• something that is likely to have potential as a weapon or means of terrorism
• something that prevents people from being productive citizens
• something that is very costly to treat of for which no effective treatment is known
• something that is chronic
• something that involves human behaviors that are very difficult to regulate
• decisions (individual or policy) that lead to conditions that cannot be sustained
• the increasing complexity of global relationships among people and among natural and human systems
• organized crime, terrorism, potential weapons systems
• environmental degradation, the limited capacities of earth to sustain growing human populations
• stress manifest psychologically, socially and politically
• tensions reflecting attitudes toward modernity
• misinformation and belief systems in conflict
• fear, mistrust, identity politics and negative stereotyping of others

MAJOR OPPORTUNITIES

• better scientific understanding of biological and ecological systems
• information systems that facilitate knowledge sharing and proactive interventions
• better understanding of complex adaptive systems
• computer modeling of different kinds and at multiple scales
• mass communications, education, social networking
• democratic deliberations regarding tradeoffs involving personal and collective interests
• the creation of policies that tend to align individual interests with collective interests and long-term sustainability

KEY WORDS AND PHRASES: (please refer to our textbook)

• Host: person, animal or thing that has the agent of a disease
• Vector: a means by which the disease moves from host to others (who become hosts)
• Clinical disease: it is medically apparent that the disease is present in a host
• Preclinical disease: the host (patent) has the disease and it will become manifest in the patient, but it is not yet manifest
• Subclinical disease: the patient has the disease, but the disease is not destined to become manifest in the patient
• Chronic disease: the patient may not be acutely ill but continues to have the disease manifest in some form
• Latent disease: the disease apparently is no longer active in the patient
• Carrier status: the host can infect others even though the disease may not be evident in the host. In some cases the host may have rare antibodies that others do not have.
• Endemic -- a population has some cases of a condition or disease at a relatively stable rate of occurrence
• Epidemic -- a local population is experiencing a substantial increase of a condition or disease which may in time to return naturally to the endemic rate
• Pandemic -- a pandemic is an epidemic experienced in many locations in different parts of the world
• Herd immunity -- a 100% rate of immunity is not required to prevent the spread of a disease through a population, depending upon the vector and the probability of transmission to persons without immunity
• Incubation period is the time it takes for a disease to "take hold" in a host and become clinically evident. If the disease is contagious during the period of incubation it is difficult to contain transmission by isolation.
• Attack rate: see pages 28 and 29. This is apparently expressed as a percent(?)

Please read EXPLORING THE OCCURRENCE OF DISEASE at the end of Chapter 2. To understand what is happening epidemiologists must consider . . .

• WHO
• WHEN
• WHERE
• HOW

To understand what is happening in a situation epidemiologists use the SCIENTIFIC METHOD and apply their knowledge of biology and the other medical sciences. Description must precede explanation. Explanation must precede an effective response.

• Observation
• Description
• Hypotheses
• Data collection
• Data analysis
• Interpretation of findings
• Design and implementation of a response

• The ideal outcome, of course, is prevention or an effective response, with as little illness and as few deaths as possible.
• The decision to do nothing is itself a decision with consequences. We cannot wash our hands of responsibility for outcomes by taking a "let it be" attitude.
• The absolute worse outcome is a seriously flawed intervention that results in great damage.