The surge in COVID-19 testing has resulted in delayed processing of COVID-19 tests around the country. The youtube channel Wendover Productions recently released an excellent video on the logistics of COVID-19 testing that describes why it is challenging to process tests quickly.
The delay in test results is impacting Allegheny County as well. In a Public Source article dated July 21, 2020, it was reported that the average time from specimen collection to test result reporting has increased from 3.9 days before July to 6.4 days in early July.
The county health department website updates the COVID-19 case counts around noon each day from the Pennsylvania National Electronic Disease Surveillance System (PA-NEDSS). The website include the number of test samples each day that tested positive. I tracked these number each day for a week to determine the distribution of reporting lag. So for example on July 22, 2020 it was reported that 95 test samples collected on July 17, 2020 had tested positive. On July 23, the number of test samples collected on July 17, 2020 that had tested positive had risen to 132. So there was a 6 day reporting lag for 37 of the test results reported on July 23.
I tracked the number of test samples collected each day that had tested positive as reported each day from July 22, 2020 to July 29, 2020. Based on this I was able to calculate the distribution in reporting delay over this one week period.
The following plots are the distribution of delays for only the test samples that tested positive. Since samples that have a higher probability of testing positive are sometimes given priority the associated delays may be less than the delays for samples that test negative.
The following histogram plot shows the number of test results with each amount of possible delay from sample collection to result reporting.
The following shows the same plot with the vertical axis showing the percent of tests during this reporting period with each amount of delay.
The cumulative percentage of results obtained after each number of days of delay is as follows.
For comparison, this medical journal article on South Korea’s contact tracing program states that all of their test results are reported within 3 days. Only 25% of Allegheny County’s test results are reported within that timeframe.
In order for a contact tracing program to be effective, the time from when the test sample of an infected person is collected and when their contacts are tested and isolated needs to be less than the serial interval between infections. The serial interval is the average amount of time between when a person becomes infected and subsequent transmission. This article in the medical journal the Lancet estimates the serial interval for COVID-19 is 6.3 days. Only 78% of test results are reported within six days. Time is needed after the results are reported to contact the person who has tested positive, identify their contacts, contact those contacts, and then for the contacts to go to a test facility and provide their test samples.
In her press conferences, Allegheny County Health Department Director Dr. Bogen has stated that they are looking into ways to reduce this delay. She stated that there is a greater delay in processing tests at national labs than in local labs. Allegheny County is working to expand local testing capacity to reduce the delays.
Hopefully this will be given high priority and will be successful as obtaining more rapid test results is necessary for an effective contact tracing program.
