Surveillance is equivalent to monitoring the () of the community

 to portray the () patterns of disease occurrence and disease potential so that investigation, control, and prevention measures can be applied efficiently and effectively. Morbidity and mortality reports are common sources of surveillance data for local and state health departments which is the information for action.

 requiring the coordinated efforts of dozens of people to characterize the extent of an epidemic and to identify its cause.  often lead to the identification of additional unreported or unrecognized ill persons who might otherwise continue to spread infection to others. For example, one of the hallmarks of investigations of persons with sexually transmitted disease is the identification of sexual partners or contacts of patients.

Surveillance and field investigations are usually sufficient to identify causes, modes of transmission, and appropriate control and prevention measures. But sometimes analytic studies employing more rigorous methods are needed. Often the methods are used in combination — with surveillance and field investigations providing clues or hypotheses about causes and modes of transmission, and analytic studies evaluating the credibility of those hypotheses.

y involves the study of disease incidence and distribution by time, place, and person. It includes the calculation of rates and identification of parts of the population at higher risk than others.

involves summarizing the distribution of diseases or healthrelated events within a population. It typically focuses on time, place, and person characteristics, such as age, sex, or socioeconomic status.

study is the use of a valid comparison group. Epidemiologists must be skilled in all aspects of such studies, including design, conduct, analysis, interpretation, and communication of findings

investigates the causes and determinants of diseases. It typically involves comparisons between groups to identify risk factors or causes. It is hypothesisdriven and often involves case-control or cohort studies

Assessing the effectiveness of interventions or programs.  is the process of determining, as systematically and objectively as possible, the relevance, effectiveness, efficiency, and impact of activities with respect to established goals

valuation of an immunization program, for example, might assess the efficiency of the operations, the proportion of the target population immunized, and the apparent impact of the program on the incidence of vaccine-preventable diseases. Similarly, evaluation of a surveillance system might address() and attributes of the system, its ability to detect cases or outbreaks, and its usefulness.

 epidemiology is often said to be a “().” During an investigation an epidemiologist usually participates as either a member or the leader of a multidisciplinary team.

 Many outbreaks cross ()and jurisdictional lines, so co-investigators may be from local, state, or federal levels of government, academic institutions, clinical facilities, or the private sector.

 Mechanisms for sustaining such linkages include official () of understanding, sharing of published or on-line information for public health audiences and outside partners, and informal networking that takes place at professional meetings.

 Developing strategies to prevent disease or control its spread

 The proportion of a population that has a particular disease at a specific time.

The number of new cases of a disease occurring within a defined period in a specific population.

Epidemiologic studies fall into two categories

he epidemiologist simply observes the exposure and disease status of each study participant. John Snow’s studies of cholera in London were observational studies. The two most common types of observational studies are cohort studies and casecontrol studies; a third type is cross-sectional studies

n this third type of observational study, asample of persons from a population is enrolled and theirexposures and health outcomes are measured simultaneously. Thecross-sectional study tends to assess the presence (prevalence) ofthe health outcome at that point of time without regard to duration.For example, in a cross-sectional study of diabetes, some of theenrollees with diabetes may have lived with their diabetes formany years, while others may have been recently diagnosed.

investigators start byenrolling a group of people with disease (at CDC such persons arecalled case-patients rather than cases, because case refers tooccurrence of disease, not a person). As a comparison group, theinvestigator then enrolls a group of people without disease(controls). Investigators then compare previous exposures betweenthe two groups. The control group provides an estimate of thebaseline or expected amount of exposure in that population. If theamount of exposure among the case group is substantially higherthan the amount you would expect based on the control group, thenillness is said to be associated with that exposure. The study ofhepatitis A traced togreen onions, described above, is an exampleof a case-control study. The key in a case-control study is toidentify an appropriate control group, comparable to the case groupin most respects, in order to provide a reasonable estimate of thebaseline or expected exposure

is similar in concept to the experimental study. In a() the epidemiologist records whether each study participant is exposed or not, and then tracks the participants to see if they develop the disease of interest. Note that this differs from an experimental study because, in a cohort study, the investigator observes rather than determines the participants’ exposure status. After a period of time, theinvestigator compares the disease rate in the exposed group with the disease rate in the unexposed group. The unexposed group serves as the comparison group, providing an estimate of the baseline or expected amount of disease occurrence in the community. If the disease rate is substantively different in the exposed group compared to the unexposed group, the exposure is said to be associated with illness.