This rate is used to determine how quickly an infectious disease may be spreading within a geographic area. An index reflects the number of new cases within a certain period and in context of a population size. Regarding COVID-19, the CDC says it looks at three metrics to determine community spread over a seven-day period per 100,000 people that includes: the number of new cases, the number of new hospital admissions and the number of inpatient hospital beds occupied by patients with COVID-19. A ‘hot spot’ would indicate that there is significant spread within a certain community.
Deeper dive
As part of public health measures aimed at reducing spread of COVID-19, the World Health Organization recommended in 2020 that communities aim for a positivity rate of less than 5% for at least two weeks. A threshold of 5% or more could be an indication that the spread of COVID-19 is not under control in the community.
If COVID-19 transmission is decreasing and more people are being tested, including those who are not infected, the positivity rate should be falling or remain below 5%, according to the Kaiser Family Foundation. In communities where the positivity rate is rising, either an insufficient share of the population is being tested and/or COVID-19 cases are increasing. It is possible that in these places, the number of new cases is increasing at an even faster rate than the confirmed case counts suggest. And a positivity rate of 10% or more indicates the likelihood that there are a relatively high number of cases and an ongoing epidemic in the state.
The CDC last outlined criteria for public health leaders in communities to use to determine policies for community mitigation measures in March 2022. The agency cautioned that it expects its criteria to be continually updated. The agency doesn’t publicly list a transmission rate threshold.
Private organizations, such as the Johns Hopkins University & Medicine Coronavirus Resource Center, have been keeping tabs on positivity rates in states to help citizens understand, on a national level, which communities may have COVID-19 spread and which do not.