CDPH tracks both probable and confirmed cases of COVID-19 to better understand how the virus is impacting our communities. Probable cases are defined as individuals with a positive antigen test that detects the presence of viral antigens. Antigen testing is useful when rapid results are needed, or in settings where laboratory resources may be limited. Confirmed cases are defined as individuals with a positive molecular test, which tests for viral genetic material, such as a PCR or polymerase chain reaction test. Results from both types of tests are reported to CDPH.
Due to the expanded use of antigen testing, surveillance of probable cases is increasingly important. The proportion of probable cases among the total cases in California has increased. To provide a more complete picture of trends in case volume, it is now more important to provide probable case data in addition to confirmed case data. The Centers for Disease Control and Prevention (CDC) has begun publishing probable case data for states.
Antigen tests are reliable, but somewhat more prone to false positive or false negative results. Thus, persons with a positive antigen test result are classified as probable cases based on national case definitions. Many antigen tests are not required to be performed in a laboratory which allows for a much quicker result.
Molecular (PCR) Tests
Molecular tests for COVID-19 include polymerase chain reaction (PCR) and other types of nucleic acid amplification test (NAAT) tests. Molecular tests are generally more sensitive and specific because they are detecting direct genetic material. Most of these tests must be processed in a laboratory, which requires waiting a day or more until results are known.
Cases that have both positive antigen test results and positive molecular test results are considered confirmed cases, and only counted once as a confirmed case.
For more information see: CDPH Factsheet for PCR, Antigen and Serology Testing
COVID-19 Cases in California: Confirmed and Probable
As of May 19, 2022
COVID-19 Cases by Test Type
As of May 19, 2022
*Testing data is updated weekly. Due to small numbers, the percentage of probable cases in the first two weeks of the month may change.