COVID Q&A: Percent positivity, how COVID-19 deaths are counted, carbon filters in masks, tests vs. cases

Q: Is it possible we’ve had a steady amount of cases in the state for many months, but we are testing more which makes it seem like our cases are rising, but in reality the infection rate hasn’t changed?

A: Comparing the number of tests with the number of cases doesn’t tell us the whole story. It makes sense that as more tests are done, more infections might be identified. For this reason, we also look at the percentage of the tests that are positive to determine if the increase in cases is a result of increased testing OR the increase in cases is because more virus is circulating. This measure, called “percent positivity,” is one way to determine how widespread infection is in the area where testing is being done.

A high percent positivity indicates high coronavirus infection rates. Even as our testing increased during June, the percent positivity increased at a higher rate because the virus was circulating in a higher percent of the population than it had been before June. When percent positivity remains unchanged, we know the new cases identified are likely a result of additional testing. Unfortunately, that was not the situation for Idaho in June and July as percent positivity rose from 2.7percent to a high of 14.85 percent. However, our percent positivity has been decreasing during August, which is a sign less virus may be circulating. Our current percent positivity is 8.3 percent.

Q: How are COVID-related deaths counted?

A: COVID-19 related death counts are based on the information provided on the death certificate by the person who certifies the death. To be counted, the certifier must indicate that COVID-19 or infection with the virus that causes the disease, SARS-CoV-2, was either an underlying cause of death or a significant condition contributing to death.

If a person has been diagnosed with COVID-19 and then dies of an unrelated cause, COVID-19 should not be reported on the death certificate. The department does not make the cause of death determination – that is made by the certifier of the death certificate, which is the medical provider or coroner.

For example, if someone has a managed condition (such as diabetes) and is diagnosed with COVID-19, and the combination of diabetes and COVID-19 complications causes the person to die, this would be counted as a COVID-related death; diabetes would also be listed on the death certificate as contributing to the death. Why? Because both conditions contributed to the person’s death.

In contrast, if a person with COVID-19 dies from trauma received in a motor vehicle accident, this would not be counted as a COVID-related death if the coroner determines that the victim’s illness had nothing to do with their death.

The professionals in Idaho who certify deaths understand the importance of a death certificate as a legal document and use the guidance provided by the National Center for Health Statistics (NCHS) to certify COVID-19 related deaths. Using the NCHS guidance ensures deaths are recorded and counted the same way throughout the United States.   

Snippet of death certificate related to cause of death
Doctors and coroners fill out a death certificate for each decedent. As you can see, there are several lines for cause of death because there may be several conditions that contributed to the death.

Q: Some masks come with replaceable carbon filters. Do they help prevent covid19?

A: Generally, thicker masks or masks with more layers are more effective at filtering out COVID-19, but they can be harder to tolerate wearing for long periods of time. As masks and face coverings become more widely available, there are lots of thing to consider, including the material of your masks and whether you should use a filter. The main rule of thumb from public health experts is that the best mask to wear is the one you can wear consistently and comfortably.

If you choose to use a filter, use one that you can breathe through and that isn’t made from materials you should not breathe in. A filter can be made from all kind of materials, but the effectiveness of carbon filters in masks is still unknown.  

The Centers for Disease Control and Prevention has good information about masks, materials, and the proper way to wear them.

Q: If someone tests positive multiple times, will that be counted as multiple cases, or are all positive tests for a single person lumped together as one case?

A: It depends on how long it’s been between tests, and other factors. The science on SARS-CoV-2 indicates an infected person can shed the virus for an extended period of time or sometimes shed it sporadically – meaning they can test positive, then negative, then positive again.

It is assumed that if a person tests positive again within 90 days of their first positive test, they are shedding the virus from their initial infection. If a person was tested again after being infected and it has been more than three months since their initial test result, they might be counted as a new case, depending on the circumstances.

To slow the spread of COVID-19 in Idaho, we all need to work together. Please remember to:

  • Keep at least six feet between you and others in public
  • Wear face coverings in public places 
  • Stay home if you are sick
  • Wash your hands often
  • Cover coughs and sneezes
  • Disinfect surfaces and objects regularly

Resources
Stay up-to-date with the latest and most accurate information on COVID-19 at the following websites:

DHW also posts lots of information, including daily updates on the numbers on Twitter, Facebook, and Instagram.

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