Quality Assurance Steps for COVID-19 Data

During the COVID-19 response in Virginia, the Virginia Department of Health (VDH) is reporting public health data in more detail and more quickly than ever before. VDH routinely performs ongoing and comprehensive quality assurance on COVID-19 cases, hospitalizations, and deaths, including those that have been previously reported to VDH. Performing data quality assurance, such as checking for correct addresses, re-classifying cases to align with national case definitions, and other efforts, is important for public health. It helps make sure that data that are reported and presented are as accurate and timely as possible. The data quality assurance steps VDH takes are not new. Public health professionals perform these data quality steps for many health conditions in addition to COVID-19. Because of these steps, it is important to note that all data are preliminary and subject to change.

Checking for Locality of Residence:

One of the data quality assurance steps that VDH takes is checking for correct addresses. VDH initially assigns a case to a locality (county or independent city) based on the patient’s residential ZIP code. In Virginia, some ZIP codes cross between multiple localities. Upon further review of the case, which includes applying geocoding to the residential address, VDH may determine the original locality assigned to the case is not correct. In these scenarios, the case will be re-assigned to the appropriate locality, which may result in a negative count for the original locality and a positive case count in the re-assigned locality.

Classifying a COVID-19 Case: 

To determine if a person should be counted as a COVID-19 case, VDH uses criteria outlined in a national case surveillance definition by the Centers for Disease Control and Prevention (CDC). Disease surveillance is foundational to public health practice. It helps understand diseases and their spread and informs appropriate actions to control outbreaks. VDH performs several steps to ensure each COVID-19 case reported in a Virginia resident meets these specified criteria.

Not every COVID-19 case involves a positive test, and not every positive test reported to VDH is counted as a COVID-19 case. Some cases are counted because they show symptoms of COVID-19 and had close contact to another known COVID-19 case as described in the national case surveillance definition. Additionally, there are people in Virginia who have been tested more than once for COVID-19. Some of these people are in higher risk settings such as healthcare or nursing homes, and others are known COVID-19 cases who needed negative tests to return to their normal routine. When a person is tested many times over the course of their COVID-19 infection, VDH reviews all the test results to ensure multiple positive test results for the same infection in one person are not counted as multiple COVID-19 cases. However, there are instances where a person may be counted as more than one COVID-19 case. This may happen when a person tests positive again more than 90 days from the first test, or when a person tests positive for COVID-19 with a different SARS-CoV-2 variant, which could indicate potential re-infection. 

The data quality steps described above may result in changes to the number of cases, hospitalizations, and deaths in your community or within the state. Negative numbers in case counts by report date on the VDH COVID-19 data dashboards may be observed as quality assurance steps are completed.


*Originally posted on June 17, 2021.