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Positivity rates

By JOHNS HOPKINS UNIVERSITY
Posted 11/25/20

The percent positive is exactly what it sounds like: the percentage of all coronavirus tests performed that are actually positive. The percent positive (sometimes called the “percent positive rate” or “positivity rate”) helps public health officials answer questions such as:...

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Positivity rates

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**What is the “percent positive” and why does it matter?

The percent positive is exactly what it sounds like: the percentage of all coronavirus tests performed that are actually positive. The percent positive (sometimes called the “percent positive rate” or “positivity rate”) helps public health officials answer questions such as:

• What is the current level of SARS-CoV-2 (coronavirus) transmission in the community?

• Are we doing enough testing for the amount of people who are getting infected?

The percent positive will be high if the number of positive tests is too high, or if the number of total tests is too low. A higher percent positive suggests higher transmission and that there are likely more people with coronavirus in the community who haven’t been tested yet.

The percent positive is a critical measure because it gives us an indication how widespread infection is in the area where the testing is occurring—and whether levels of testing are keeping up with levels of disease transmission.

**What does a high percent positive mean?

A high percent positive means that more testing should probably be done—and it suggests that it is not a good time to relax restrictions aimed at reducing coronavirus transmission. Because a high percentage of positive tests suggests high coronavirus infection rates (due to high transmission in the community), a high percent positive can indicate it may be a good time to add restrictions to slow the spread of disease.

**How high is too high?

The higher the percent positive is, the more concerning it is. As a rule of thumb, however, one threshold for the percent positive being “too high” is 5%. For example, the World Health Organization recommended in May that the percent positive remain below 5% for at least two weeks before governments consider reopening.