Skip to ContentGo to accessibility page

Key Terms

antigenic drift
when viruses undergo minor mutations each year, such as the influenza A viruses
antigenic shift
when viruses undergo a major mutation; has occurred with flu viruses four times over the past 100 years
case definition
a set of criteria used to define a disease for the purpose of public health surveillance
case surveillance
when public health agencies collect information about an individual diagnosed with a health condition that could potentially pose a health threat to others
emerging infectious diseases (EIDs)
diseases that are newly affecting populations or diseases that have existed previously but only caused isolated disease that are now increasing in incidence and geographic range
erythema migrans (EM)
also known as the “bull’s eye” rash of Lyme disease; is erythematous, annular, and homogenous at the site of the actual tick bite and expands over several days to sizes greater than 5 centimeters in diameter with a central clearing as the rash expands
infectious
easily transmitted between individuals
infectious disease
disease caused by pathogenic microorganisms such as bacteria, viruses, parasites, or fungi; enters a human host, multiplies, and causes infection that can spread to others
microcephaly
condition where a baby’s head is smaller than expected, impacting brain development
nationally notifiable condition
a disease required by law to be reported to government authorities, allowing for case surveillance to assess transmission patterns and determine interventions to control outbreaks
pandemic
an epidemic that spreads worldwide
pathogenicity
the potential ability to cause disease; the more pathogenic an agent is, the greater the ability it has to cause disease in a susceptible host
public health surveillance
the ongoing, systematic collection, analysis, and interpretation of health-related data essential to planning, implementation, and evaluation of public health practice
vectors
living organisms, such as ticks and mosquitoes, that can transmit infectious pathogens to humans
Citation/Attribution
Reuse and redistribution of this content in digital or print format:
  • This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's prior written permission.
  • This book uses the Creative Commons Attribution-NonCommercial-ShareAlike License, which means that you can reuse and modify the material only for noncommercial purposes, must attribute OpenStax, and must distribute any derivative works under the same license.
  • Any commercial printing of this textbook, including using a local or custom printer, must be approved by OpenStax, and proper citation provided.
  • OpenStax-copyrighted images, activities, assessments, and similar components of this book are subject to the same licensing – CC-BY-NC-SA. They can be used for noncommercial purposes with attribution. Commercial use requires permission.
  • Permission requests: Anyone who intends to incorporate this content (including text, images, and other components) into large language models, use it in AI offerings, use it commercially (including in print), and/or has questions about another use case is welcome to complete our reuse request form.
Attribution information
  • If you are redistributing all or part of this book in a noncommercial print format, then you must include on every physical page the following attribution:

    Access for free at https://openstax.org/books/population-health/pages/1-introduction

  • If you are redistributing all or part of this book in a noncommercial digital format, then for every page that includes OpenStax content, you must license the derivative work under the same CC-BY-NC-SA license as the original, and include on every digital page view the following attribution:

    Access for free at https://openstax.org/books/population-health/pages/1-introduction

Citation information

The information below includes the information needed to generate citations in most major styles (APA, MLA, etc.); you must reformat and organize the information as needed to fit the requirements of the style. Use the information below to generate a citation. We recommend using a citation tool such as this one.

© Apr 23, 2026 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike License. The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo, and Rice University name, and Rice University logo trademarks, or wordmarks are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.