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Figure 1. An aggregate view based on a number of different published studies. 3-10 It outlines the likelihood that an
individual patient will have a positive test result at a specific time after onset of symptoms. Day 0 is time of symptom onset.

The purpose of this document is to help clinicians Time Course
understand the important issues regarding testing, including: Although there is a vast amount of individual
variability in response to viral exposure, understanding
• The types of testing available. the general time course of exposure, onset of symptoms,
• Assessment of the reliability of these tests. length of viral shedding, and production of antibodies is
• Using test results to provide a framework for important for deciding which test to order and how to
clinical decision–making for patients. interpret the subsequent results.
Figure 1 gives a general view of the time course of
Laboratory testing for SARS-CoV-2 includes two main exposure, symptoms, and viral and immune response testing
categories: those that detect the presence of the virus and results. A number of things should noted based on the figure.
those that determine the host response to the virus by Time of exposure to symptom development ranges
detecting antibodies specific to SARS-CoV-2. Transmission from 2-21 days.
2
of SARS-CoV-2 can occur from direct contact or via airborne
droplets. There are several possible responses after an • >90% of people who develop symptoms will do so
individual is exposed to the virus, as shown in the table below. within 14 days.
A similar table is included in the summary, with inclusion of • Up to 10% of people may develop symptoms later
clinical interpretation and recommended action. than 14 days.
• Many people never develop symptoms but may still
Possible Outcomes After Exposure to SARS-CoV-2 develop antibody responses. The timing and level
of antibody responses in asymptomatic people is
Viral RNA Production of presently unknown.
Symptomatic shedding (RNA) antibodies (Ab)
- - - Viral shedding can begin 3-21 days after exposure
- + - (i.e., preceding symptoms).
- - +
- + + • Viral RNA shedding can occur in nasopharynx,
oropharynx, saliva, and sputum for up to 21 days
+ - - after symptom resolution.
+ + - • Testing evaluates viral RNA, not shedding of intact
+ - + virus (i.e., infectivity).
+ + + • It appears that intact viral shedding is complete
14 days after symptoms begin, though viral RNA
shedding continues (as noted above).

Messier—Primer on SARS-CoV-2 Testing Integrative Medicine • Vol. 19, No. S1 • Epub Ahead of Print 45