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Cracking the code of case data

Though the Virginia Department of Health cautions that ZIP code data it started to compile last week is incomplete, it is the most local data it has released on the number of positive COVID-19 cases and tests that have taken place.

The state health department suppressed some data for some ZIP codes for privacy purposes — those it said had between one and four positive cases.

Examples of this regionally include the 23304 ZIP code in the Battery Park area of Isle of Wight County, about three miles east-northeast of Smithfield, with just six testing encounters, the 23432 ZIP code in Suffolk, which includes the Chuckatuck, Sandy Bottom and Cherry Grove areas of the city, and the 23827 ZIP code in the south-central part of Southampton County,  which includes Shiloh and Boykins.

The state health department also did not have ZIP code data for 582 COVID-19 positive cases as of May 15, and it has tested 2,802 people who live out of state.

“VDH has county data on every case and laboratory report, but we do not have ZIP code data on every record,” the state health department says on its website. “Because this field is not complete, the total number of cases and tests by ZIP code may not match the same total count by county.”

When Gov. Ralph Northam was asked April 27 about providing case data by ZIP codes so people would know whether COVID-19 was impacting their communities, he said the information would be important to allow different regions or localities to know how they were doing regarding the coronavirus pandemic.

State health commissioner Dr. Norman Oliver, at the same briefing, said the state was exploring the use of heat maps to give people an idea of where concentrated cases of COVID-19 were, and said that the information the state health department was already providing at the locality level, without the demographics, was “a lot more granular.”

“The issue with ZIP code, we believe, is that ZIP codes can be problematic,” Oliver said. “The ZIP codes here in the Richmond area that include both Richmond and Henrico … would not be, really, a good data point for someone to understand the actual distribution of what was going on. Doing it at the jurisdiction level, it’s actually far better, we believe.”

Still, two days later, Northam said the state would provide the data, and it began reporting ZIP code-level data May 7. According to the state health department, ZIP code data is based on where a patient lives, and not the location where they were tested or treated.

The state health department noted that ZIP codes do not necessarily match city, town and county borders, which it says makes it difficult to it to look at rates of positive COVID-19 tests per 100,000 population, a way in which it looks for patterns in disease data. Other ZIP codes, because they are in industrial or commercial areas, were grouped together with other ZIP codes in what it called ZIP Code Tabulation Areas.

In the Western Tidewater Health District — encompassing Suffolk and Franklin, along with Southampton and Isle of Wight counties — the largest number of positive COVID-19 cases have been in the 23434 ZIP code of Suffolk, with 147 positive cases and 1,188 testing encounters.

Another Suffolk ZIP code, 23435, has had 96 positive cases and 617 testing encounters.

In total, Suffolk has had 255 positive cases of COVID-19 and 22 deaths.

In Southampton County, the highest number of positive COVID-19 cases has been in the 23829 ZIP code, with 78 cases and 458 testing encounters coming in the Capron area of the county.