Links To And Excerpts From COVID-19 Appendices From The CDC –

In this post, I link to and excerpt from the CDC web page on COVID-19, Appendices. Updated Aug. 5, 2021.

Appendix A, which I’ve included in its entirety below, contains the CDC’s definitions for close contacts. Determining whether a person has had close contact with a COVID-19 patient is of critical importance.*

*Please see Which Persons Are At Increased Risk When Exposed To COVID-19 Infected Persons And Why It Matters: Links To And Excerpts From The “FACT SHEET FOR HEALTH CARE PROVIDERS EMERGENCY USE AUTHORIZATION (EUA) OF REGEN-COVTM (casirivimab and imdevimab)” From The FDA
Posted on August 23, 2021 by Tom Wade MD

All that follows is from the CDC web page on COVID-19, Appendices. Updated Aug. 5, 2021.


Updated Aug. 5, 2021

Revisions made on August 5, 2021

  • Updated the close contact definition.
Appendix A – Glossary of Key Terms



Case Investigation & Contact Tracing

Fundamental activities that involve working with a patient who has been diagnosed with an infectious disease to identify and provide support to people (contacts) who may have been infected through exposure to the patient. This process prevents further transmission of disease by separating people who have (or may have) an infectious disease from people who do not.

Close Contact

Close Contact through Proximity and Duration of ExposureSomeone who was within 6 feet of an infected person (laboratory-confirmed or a clinically compatible illness) for a cumulative total of 15 minutes or more over a 24-hour period (for example, three individual 5-minute exposures for a total of 15 minutes)An infected person can spread SARS-CoV-2 starting from 2 days before they have any symptoms (or, for asymptomatic patients, 2 days before the positive specimen collection date), until they meet criteria for discontinuing home isolation.

  • Exception: In the K–12 indoor classroom setting, the close contact definition excludes students who were within 3 to 6 feet of an infected student (laboratory-confirmed or a clinically compatible illness) if both the infected student and the exposed student(s) correctly and consistently wore well-fitting masks the entire time.

This exception does not apply to teachers, staff, or other adults in the indoor classroom setting.

Public Health Recommendations:

Except in certain circumstances, people who have been in close contact with someone who has COVID-19 should quarantine. However, the following people with recent exposure may NOT need to quarantine:

Additional Information:

A number of factors can influence a person’s risk of exposure to COVID-19, including the type, proximity, and duration of their exposure, environmental factors (such as crowding and ventilation), vaccination statusprior COVID-19 infection, and mask use.

Correct and consistent mask use is a critical step that people can take to protect themselves and others from COVID-19. However, the type of masks used and whether they are used consistently and correctly varies throughout the general population. Except in K–12 indoor classroom settings as described above, mask use is not considered when defining a close contact during case investigation and contact tracing, regardless of whether the person diagnosed with COVID-19 or the person exposed to SARS-CoV-2 was wearing a mask. (Note: Exposure risk in the healthcare setting is determined separately and outlined in CDC guidance).

Confirmed COVID-19 Case

Report of person with COVID-19 and meeting confirmatory laboratory evidence.

Contact Elicitation Window

The timeframe when the case was likely infectious and not under isolation. This is the time period for which possible contacts should be elicited.


Having come into contact with a cause of, or possessing a characteristic that is a determinant of, a particular health problem. Principles of Epidemiology in Public Health Practice.


Law enforcement, fire services, emergency medical services, and emergency management officials. EMS Guidance.

Healthcare personnel

All paid and unpaid people serving in healthcare settings who have the potential for direct or indirect exposure to patients or infectious materials, including body substances; contaminated medical supplies, devices, and equipment; contaminated environmental surfaces; or contaminated air. Potential Exposure at Work.

Incubation period

Period of time between exposure to an infection and onset of symptoms


The separation of a person or group of people known or reasonably believed to be infected with a communicable disease and potentially infectious from those who are not infected to prevent spread of the communicable disease. Isolation for public health purposes may be voluntary or compelled by federal, state, or local public health order.

Multigenerational Household

Households that consist of more than two generations living under the same roofexternal icon. Many researchers also include households with a grandparent and at least one other generation.

Probable COVID-19 Case

Report of person meeting clinical AND epidemiologic evidence of COVID-19 but without confirmatory laboratory evidence. More about Probable COVID-19 Case pdf icon[252 KB, 10 Pages]external icon.


The separation of a person or group of people reasonably believed to have been exposed to a communicable disease but not yet symptomatic from others who have not been so exposed to prevent the possible spread of the communicable disease. Quarantine may be voluntary or compelled by federal, state, or local public health order.

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