COVID-19 data questions

Learn about how our San Francisco COVID-19 data is updated and why it might be delayed.

Data update schedule

Data shown on the Tracker are the most reliable and accurate data available.  

Check each dashboard or dataset to find out when it updates. Dashboards will not update on the business day following any federal holiday. 

The list below shows the steps we must take get accurate data: 

  1. COVID-19 test is collected by a health care provider 

  1. Tests sent to laboratories to process the test 

  1. Laboratories report test results to the City 

  1. City validates the data and resolves any data issues 

These steps take a significant amount of effort by medical providers, labs, and City staff. Read below for more details on steps 2, 3, and 4. 

Lab processes and reports test results 
There are many labs processing tests. These labs include: 

  • commercial labs 

  • clinical labs 

  • hospital labs  

  • the San Francisco Public Health Laboratory 

Once a lab processes the test, they then report the result to the City.  

City validates results and resolves errors 
Once the City receives test results data, we must validate the data resolve any data issues. During this step, staff may uncover gaps or problems in the data. This sometimes is because labs did not report results correctly. The City then has to reach out to the lab to correct the data.  

For positive tests, the City completes more verification and interviews. They must confirm if the case is a resident of San Francisco.

Changes to case and test data for prior days

The City depends on data reported by private and public labs and providers. Lab staff try to compile test results by close of business and report them to the City the next morning. 

Tests and cases can increase or decrease for previous days because of: 

  • lab processing time 

  • data validation time 

  • case investigation results 

Lab processing time 

Labs analyze and report on high volumes of tests every day. They may not be able to analyze and report on all tests collected that day because there were too many. This means labs may report results from prior days at the same time they report on the current day.  

Data validation time 

During data validation, the City sometimes identifies errors or delays. The City will not report a test result that may be an error. The lab must take time to fix these errors. The fix may result in data added or corrected for previous days.  

Case investigation results 

The city completes case investigations with every positive test. During this process, staff may discover duplicates or data errors. For example, some tests are for persons living outside of the City. Some are copies of previously submitted results. These are not included in the total San Francisco COVID-19 case count.  

Process of reporting results for prior days

Below is a diagram showing how data comes to the City and is then reported to the public. 

The total positive tests will go up by the number of tests reported. The days on which individuals tested positive might be earlier. 

An example is shown in the image below. The image assumes on April 2nd, two positive test results were reported for the day. 

On April 2nd, you would you would see 2 positive cases for the day. In the final section of the image, these are the two grey boxes for 4/2/20.  

On April 3rd, if you looked at the total cases for April 2, you would see something different. You would now see 3 positive cases for April 2nd. This is because Lab 2 reported another case for that day. In the final section of the image, that case is the green box for 4/2/20. 

This image shows why public data on the tracker might show different data for prior days. If a lab is not able to process all tests on a single day, they may submit a report to the City with results from prior days and the current day. The City would then update prior days' data with these missing test results.
Last updated July 16, 2021