SARS-CoV-2, the virus that causes coronavirus illness 2019 (COVID-19), laboratory knowledge from public well being laboratories, U.S. hospital laboratories, personal and business laboratories, some giant chain drug shops, and different testing entities are reported to state and native well being departments. Laboratory knowledge are reported to state and native well being departments in accordance with relevant state or native regulation and transmitted to CDC in accordance with the Coronavirus Assist, Aid, and Financial Safety (CARES) Act (CARES Act Part 18115pdf iconexterior icon). De-identified COVID-19 laboratory knowledge from 6 giant business and public well being laboratories are additionally reported on to CDC. Hospital laboratories in states that aren’t but sending line-level knowledge to CDC report knowledge on to the Division of Well being and Human Providers. These entities voluntarily submit digital recordsdata of COVID-19 de-identified laboratory knowledge to CDC or HHS on a day by day or periodic foundation. At CDC and HHS, the info are processed and analyzed, with the outcomes made out there for federal response efforts (in HHS Shield). Laboratory knowledge offered to CDC is made publicly out there on CDC’s COVID Knowledge Tracker web site in a manner that protects the privateness of people and will be downloaded for evaluation from healthdata.govexterior icon.
Utilizing % Positivity Calculation for Public Well being Surveillance
The method for calculating % positivity utilized by CDC is the variety of constructive assessments (numerator) divided by the entire variety of resulted reported assessments (denominator): (constructive/complete) x 100% the place the entire equals constructive plus adverse take a look at outcomes and excludes indeterminate outcomes.
Normally, for federal COVID-19 response reporting functions, laboratory take a look at % positivity has represented the share of all RT-PCR assessments carried out which can be constructive. Though the strategies utilized by totally different organizations to calculate % positivity can differ (see beneath), % positivity has offered insights into transmission of infectious illnesses, together with COVID-19 (SARS-CoV-2), in a geographical space (e.g., nationwide, regional, state, county). The interpretation of % positivity is dependent upon the amount of COVID-19 diagnostic laboratory testing reported to state and native well being departments and the standards used for figuring out what populations are examined (routine screening of asymptomatic individuals vs diagnostic testing of symptomatic individuals or case contacts).
A excessive COVID-19 RT-PCR % positivity happens when most of the take a look at outcomes amongst these being examined and reported in a group are constructive. This will imply that
- there are widespread infections in the neighborhood examined; or
- solely a subset of the group at biggest threat for SARS-CoV-2 an infection is being examined; or
- there are reporting processes or delays that skew the outcomes (e.g., prioritizing reporting of constructive take a look at outcomes over adverse outcomes).
The laboratory take a look at % constructive goes down when extra folks examined are adverse. This occurs when the variety of infections goes down (the numerator will get smaller), or testing is expanded to extra people who find themselves not contaminated (the denominator is bigger with out uncovering lots of new infections). Normally, % positivity will go down as extra individuals are being screened in non-outbreak settings (e.g., routine screening in colleges, long-term care amenities, workplaces) and the outcomes are reported. Expanded testing doesn’t at all times cut back the % constructive when there may be widespread transmission; it could reveal extra people who find themselves contaminated.
Totally different Strategies Used to Calculate % Positivity
CDC, state, and jurisdictional well being departments could calculate % positivity in a different way, which can embrace:
- Variations within the numerators or denominators used (e.g., assessments/assessments, folks/assessments, folks/folks). State and jurisdictional well being departments have entry to non-public identifiers of their datasets and might determine and de-duplicate individuals with a number of constructive assessments whereas CDC is unable to carry out this perform.
(See Determine 1 beneath.)
- Variations within the timeframe by which knowledge are included (i.e., a seven-day verses a 14-day rolling common), in addition to what dates (e.g. specimen assortment date, take a look at date, end result date) are used to assign assessments to particular timeframes.
- Variations within the inclusion or exclusion of antigen take a look at outcomes. Antigen assessments could also be used for screening or diagnostic functions. Constructive take a look at outcomes for COVID-19 antigen are thought of a possible case as outlined within the CSTE place assertion, and won’t be confirmed utilizing FDA approved RT-PCR assessments for COVID-19. Antigen take a look at outcomes won’t be constantly reported to public well being by clinics or websites the place routine screening is carried out (e.g., long-term care amenities, colleges or workplaces).
- Variations in inclusion of screening assessments outcomes. With elevated screening utilizing each antigen and RT-PCR assessments, the power to confidently interpret the which means of % positivity outcomes can be impacted by the unknown standards for testing (routine screening versus diagnostic testing of symptomatic individuals).
- Variations in how take a look at outcomes are assigned to jurisdictions, together with by the individual’s place of residence, the supplier’s clinic location, the situation the take a look at specimen was collected, or the situation of the laboratory.
Determine 1: 3 ways by which % positivity will be calculated for COVID-19 laboratory assessments
CDC Strategies for Calculating % Positivity
Presently, for federal reporting functions, CDC defines % positivity because the variety of COVID-19 constructive RT-PCR assessments because the numerator (contains diagnostic assessments and screening assessments, when analyzed at CLIA-certified laboratories), divided by the entire variety of RT-PCR assessments with constructive and adverse outcomes because the denominator: (constructive assessments/complete assessments) x 100% (Technique 1 within the determine above). This excludes antigen assessments, antibody assessments, and RT-PCR assessments carried out by non-CLIA laboratories for surveillance functions. Knowledge acquired on the federal degree are de-identified and, due to this fact, are usually not capable of be linked on the individual degree for de-duplication. This prevents CDC use of strategies 2 (folks over take a look at) and three (folks over folks) in Determine 1 above.
Resulted assessments in knowledge offered to CDC by states and native well being departments are assigned to a 7-day timeframe primarily based on the highest test-related date out there within the knowledge in line with the next hierarchy:
- Check date (day the laboratory had a take a look at end result)
- End result date (day the laboratory despatched the end result to the requestor)
- Specimen acquired date (day accessioned by lab)
- Specimen assortment date (day specimen collected from affected person)
Check outcomes are assigned to a geography primarily based on a hierarchy of test-related areas:
- Affected person location
- Supplier facility location
- Ordering facility location
- Performing group location
Knowledge assets the place % positivity for COVID-19 are at the moment reported
CDC at the moment offers knowledge on the nationwide degree on RT-PCR laboratory take a look at % positivity on the CDC COVID Knowledge Tracker web site.
The Middle for Medicare and Medicaid Providers publishes % positivityexterior icon by county to information the frequency of COVID-19 screeningpdf iconexterior icon of long-term care facility residents and employees.
The White Home Coronavirus Process Drive stories % positivity on the nationwide, state and county ranges within the Governor’s Report, a weekly report that despatched by the Vice President to every Governor.
- Totally different methodologic decisions for calculating % positivity when constantly utilized are helpful for monitoring developments and magnitude for surveillance functions and choice making.
- State and native officers could contemplate adopting some or the entire strategies outlined above if these strategies swimsuit their surveillance wants.