British investigators conducted a study to compare measles-mumps-rubella (MMR) vaccine history among 1,294 children with pervasive development disorder (e.g., autism and Asperger’s syndrome) and 4,469 children without such disorders. (They found no association.) This is an example of which type(s) of study? (Choose one wrong answer)

Correct Answer: C

Rationale: This is an observational case-control study (B, D), not cohort (C).

Correct Answer: B

Rationale: Surveillance definitions focus on detection, differing from clinical treatment focus.

Correct Answer: D

Rationale: The principle of multicausation emphasizes that an infectious agent alone is not sufficient to cause disease; the agent must be transmitted within a conducive environment to a susceptible host. Mycobacterium tuberculosis kills cells. M. tuberculosis has low infectivity, low pathogenicity, but high virulence if untreated.

Correct Answer: B

Rationale: Standardized definitions of diseases are necessary for public health monitoring and surveillance across all levels of government. Diseases are defined and classified according to confirmed cases, probable cases, laboratory-confirmed cases, clinically compatible cases, epidemiologically linked cases, genetic typing, and clinical case definition. Once defined, disease occurrence can be compared across time, populations, and geographic areas, and appropriate control efforts can be implemented.

Correct Answer: C

Rationale: The incidence rate of new cases would be most useful for detecting short-term acute disease changes, because the swine flu duration is usually relatively short. The prevalence rate is the number of all cases of a specific disease or condition in a population at a given point in time. Crude death rates summarize the occurrence of mortality. An age-specific death rate characterizes the death rates of a particular age group in the population.