Case-case comparisons to study causation of common infectious diseases

Area of Science:

• Epidemiology
• Infectious Disease Research
• Biostatistics

Background:

• Reportable infectious disease studies often rely on limited, non-randomly selected cases from surveillance systems.
• Standard case-control studies face biases from surveillance selection and differential recall between cases and controls.
• Comparing cases to other cases from similar surveillance systems can mitigate some biases but introduce others.

Purpose of the Study:

• To introduce and evaluate the case-case comparison methodology for infectious disease research.
• To address biases inherent in traditional case-control studies for analyzing exposure histories.
• To refine the analysis of specific exposures associated with infectious agent transmission.

Main Methods:

• Subtyping pathogens within infectious disease cases to create etiologically meaningful subgroups.
• Comparing exposure histories between these distinct case subgroups.
• Utilizing laboratory typing techniques to enable case-case comparisons.

Main Results:

• Case-case comparison removes several biases associated with traditional case-control studies.
• The control group (other cases) provides a predictable contrast to the study base's exposure history.
• Analysis is focused and more precise on factors directly linked to exposure to the infecting agent.

Conclusions:

• Case-case comparison is an advancement in case-control methodology, enabled by pathogen subtyping.
• This approach allows for a more restricted yet refined analysis of specific exposure-infection associations.
• It efficiently and unbiasedly determines how exposure to an infectious agent occurred, though it cannot study general disease occurrence factors.