The When To Test Calculator for Individuals defines a hotspot as an area in which the COVID-19 prevalence is at or above 3%.
I checked my recommended testing strategy with both When To Test Calculators, and I got different results. Why did that happen?
The two Calculators have slightly different goals and base their recommendations on different inputs.
The goal of the When To Test Calculator for Individuals is to reduce the spread of disease in a given geographic area at a specific time. It does that by recommending that an individual get tested when it's more likely that they might be about to pass COVID-19 on to others. (This Calculator is a decision-support tool only. Results are provided for informational purposes and should not be construed as medical advice.)
The goal of the When To Test Calculator for Organizations is to decrease the overall risk of an outbreak within a workplace or school. It does that by evaluating the COVID-mitigation strategies in place at the organization and recommending the appropriate level of testing needed to complement those strategies.
For all of those reasons, when you use the two tools you might get different results. If your personal and organizational recommendations differ, consider taking both into account when deciding how often you should get tested for COVID-19.
How do my past and future contacts help the When To Test Calculator for Individuals figure out whether I need to be tested?
The Calculator tells you whether you need to be tested in order to prevent the spread of COVID-19 in your community.
The number of people with whom you were in contact last week - along with the prevalence of COVID-19 in your area - tells the Calculator how likely it is that you have been infected with COVID-19.
The number of people with whom you plan to be in contact next week tells the Calculator how likely it is that you will infect other people.
The Calculator uses those factors and other inputs to develop a recommendation about whether you need to be tested in order to help stop the spread of COVID-19 in your area.
I'm vaccinated. How will that affect my testing recommendation from the When to Test Calculator for Individuals?
All currently authorized COVID-19 vaccines are highly effective at preventing hospitalization, severe disease, and death due to the SARS-CoV-2 virus. People who are fully vaccinated are also less likely to become infected with SARS-CoV-2 at all, which means they are less likely to spread COVID-19 than unvaccinated people are. For that reason, the number of contacts that would trigger a recommendation to get tested will be higher if you're fully vaccinated.
How does mask-wearing affect my test recommendation from the When to Test Calculator for Individuals?
The When To Test Calculator for Individuals tells you whether you need to be tested in order to prevent the spread of COVID-19 in your community.
Wearing a mask significantly reduces both your risk of getting COVID-19 and the chance that you'll pass on the disease if you do get infected. As a result, the number of contacts that would trigger a recommendation to get tested will be higher if you wear a properly fitted mask when you're in close contact with other people.
Both When to Test Calculators are based on CDC guidelines. Current guidelines define a “close contact” as someone who was within six feet of an infected person for a total of at least 15 minutes over the course of 24 hours. One exception to that rule is applicable only to schools: Students who were between three and six feet of an infected person are not considered close contacts as long as they were in school and “correctly and consistently” wearing masks.
I've already had COVID-19. How will that affect my testing recommendation from the When to Test Calculator for Individuals?
If you've been infected with SARS-CoV-2 (the virus that causes COVID-19), your risk of getting infected again is lower for a period of time. However, it's not clear exactly how much lower that risk is; it might depend on how severe your case was and what variant you were infected with. It's also not clear how long the protection lasts.
For those reasons, the When To Test Calculator for Individuals assumes that prior infection only gives you a relatively small amount of protection from future disease, and that the protection is temporary.
The When to Test Calculator for Individuals recommended that I get tested for COVID-19. What should I do now?
The When To Test Calculator for Individuals is a tool intended to help you decide whether you should get tested for COVID-19 in order to keep from spreading the disease to other people. If you get this recommendation, your risk of spreading the disease will be lowest if you get tested before coming into close contact with anyone outside your household. (This Calculator is a decision-support tool only. Results are provided for informational purposes and should not be construed as medical advice.)
COVID-19 tests are available at no cost to anyone in the nation, including the uninsured. Visit the US Department of Health and Human Services website to find a free testing site near you. You can also contact your health-care provider or your state or local public health department for more information.
I thought my organization's mitigation strategies were adequate, but I get a warning message when I input those strategies. Why is this happening?
There are three main reasons why you might get that result.
- Your mitigation strategies aren't strong enough.
- The turnaround time for the test is too long.
- Your organization doesn't offer testing on enough days of the week.
Regardless of the reason why you received the warning message, improving mitigation strategies (incentivizing vaccination among employees, emphasizing consistent mask-wearing, keeping better track of close contacts, and/or decreasing the size of cohorts that participate in unmasked activity together) is the best way to lower your organization's risk of an outbreak.
There are a lot of different kinds of antigen tests out there. How do I select one for my organization to use?
In addition to the cost of the individual test kits, the following criteria can inform your choice:
Accuracy: Most antigen tests have a very high specificity. However, the sensitivity of the different brands of tests varies. The When to Test Calculator for Organizations assumes a lower sensitivity for Antigen tests than with PCR tests, to ensure that the recommended testing frequency is adequate to prevent an outbreak.
Capital expenditures and maintenance: Some antigen tests run on a small testing instrument, which must be purchased separately and maintained over time. Depending on size of your organization, you may need to purchase several of these instruments in order to be able to test your population quickly enough to prevent an outbreak.
Staffing requirements: Some antigen tests require trained staff to obtain samples and/or run the tests. If you use an instrument-based antigen test, you will need staff to maintain the instruments, as well. Other types of antigen tests can be performed entirely by the person being tested.
Time: Some rapid antigen tests can be done at home, decreasing the amount of time taken away from work or school for testing purposes.
Access: Manufacturing of antigen tests has not always kept up well with demand, so some businesses may find they have a limited selection of brands from which to purchase. Some schools will only have access to a single type of antigen test, which is provided or mandated by the state.
My organization is being provided with tests or has already implemented a testing program. How can I apply what I learn from the When To Test Calculator for Organizations to this situation?
You can find the list of test types for which the Calculator provides results under the FAQ topic “What are the main differences between the various test types listed on the results page for the When To Test Calculator for Organizations?” If you’re not sure which type of test you are or will be using, check with your test vendor for confirmation.
Once you know your organization’s type of test, look at your results in calculator and find the row that matches your test type. (If you’re using pooled testing, you may need to click on “View More Pooling Options” to find the type of follow-up testing your program is or will be using.) The results on that row are the Calculator’s recommended test frequency for your organization.
If the Calculator’s recommendations for your test type aren’t feasible for your organization, or if they indicate that you cannot prevent an outbreak using that type of test, consider how your organization might improve mitigation measures other than testing. By emphasizing consistent mask-wearing, incentivizing vaccination among employees, keeping better track of close contacts, or decreasing the size of cohorts that participate in unmasked activity together, you can decrease your organization’s reliance on testing as a mitigation measure. Use the Calculator to model various scenarios and predict how improvements in these areas can change your test recommendations.
What are the main differences between the various test types listed on the results page for the When To Test Calculator for Organizations?
The amount of testing your organization needs to do depends in part on the type of test you use. This Calculator returns results for the test categories listed in the table below, as well as additional results for other pooled testing strategies.
NOTE: The test categories shown in the Calculator are examples only; they do not represent any one individual test.
For more information, see the following FAQ topics:
PCR tests, also known as molecular tests, look for pieces of the virus’s genetic material using a lab technique called polymerase chain reaction (PCR). They are the most accurate kind of test for COVID-19 currently available.
PCR samples are usually sent for processing and analysis in a lab, and results can take anywhere from a few hours to several days to arrive. Lab-based PCR tests tend to be more costly than other types of test. Some point-of-care PCR tests are now available, but they typically require purchase of a dedicated instrument and training to run the tests. If you want to use a point-of-care PCR test to screen members of an organization, you may need to purchase multiple instruments and train several staff members for this purpose. Point-of-care PCR tests typically return results in under an hour.
Antigen tests look for viral proteins. These tests typically provide results within minutes and are very good at accurately identifying people who are shedding a lot of virus particles. They are not as good as PCR tests are at finding people who aren't carrying as much virus, including children and asymptomatic adults. If you are using this type of test in an organizational setting, be sure to understand how well the particular brand you use works in the population you’ll be testing (adults vs. children, people with symptoms vs. people without symptoms). Many antigen tests still require trained staff to run them, but a few are now available over the counter. Antigen tests tend to be the least expensive type of test.
Because of their decreased sensitivity, antigen tests have the following limitations:
- If you are using antigen tests to screen members of an organization, you may need to test more frequently than you would if you were using a PCR test in order to prevent an outbreak.
- Positive results on antigen tests whose specificity is >99% are usually correct, but negative results may need to be confirmed with a PCR test.
Remember, no test is perfect.
R0 (R-naught) is a measure of the average number of people who will contract a contagious disease from one infected person. It’s a measure of viral transmissibility, or how fast the disease is spreading.
When R0 is exactly 1.0, it means that, on average, one infected person will infect one other person. When R0 is less than 1.0, it means that the spread of the disease is decreasing within the community. When R0is above 1.0, the spread of disease is increasing. The more transmissible a disease or disease variant is, the higher its R0.
The When to Test Calculator for Organizations bases its default R0 on CDC estimates regarding the transmissibility of the most prevalent variant of COVID-19 in the US, which is currently the Delta variant. The Calculator's default R0 for Typical conditions reflects the CDC's low-end estimate of Delta's R0, while the default setting for Hotspot conditions reflects a higher-end estimate of Delta's R0. If you know which variant is most common in your area and wish to change the R0 in your scenarios to reflect that variant, click on "Show Advanced Settings," then "Main Calculator Settings,” and scroll down to "Estimated R0."
For the purposes of the When To Test Calculators, prevalence is the percentage of individuals in a population who are infected with COVID-19 at any given moment. If there are 100 people in a building and one person has COVID-19, then the prevalence of COVID-19 in that building is 1%.
The prevalence default settings for the When To Test Calculator for Organizations are 1% for typical conditions and 3% for hotspot conditions. To adjust these settings, click on the Show Advanced Settings button on the results page, open the Main Calculator Settings tab, and scroll down to the Prevalence settings (green arrows below).