COVID-19 positivity rate plunges across city zip codes

COVID-19 positivity rate plunges across city zip codes

By Denise Dunbar |

Alexandria’s cumulative COVID-19 positivity rate has declined in each of the five zip codes that lie fully within city limits since data was first released on May 7.

The combined positivity rate in zip codes 22301, 22302, 22304, 22305 and 22314 was 28.2% on May 7, according to calculations made to data from the Virginia Department of Health. There were 862 confirmed positive COVID-19 tests out of 3,061 conducted at that time.

That total starkly contrasts with the combined 8.5% positivity rate on confirmed cases of COVID-19 per test within those five zip codes since May 7.

The decline is even more pronounced since June 9, when the second detailed batch of zip code data was released by the VDH. The combined positivity rate of those Alexandria zip codes for test results received in the past six weeks totals 4.6%.

The only uptick has occurred since the July 7 data was released: The aggregate positivity rate for zip codes 22301, 22302, 22304, 22305 and 22314 for test results received in the two-week period ending July 21 had nudged up to 5%.

Despite the slight increase, Alexandria’s two-week aggregate positivity rate is considerably lower than the Commonwealth of Virginia’s seven-day moving average rate of 7.7% positive tests as of July 17.

One reason for the state’s higher positivity rate is that it includes both confirmed and probable cases, while the zip code data provided by VDH lists confirmed cases only. The VDH website defines probable cases as ones that are “symptomatic with a known exposure to COVID-19” but that lack a positive test result.

The extremely high early positivity rate can be partially explained by the fact that because tests were scarce until early May, only the sickest people were receiving COVID-19 tests early in the pandemic. By May 1, more than 100 test results per day consistently began to be received in Alexandria, according to data on the VDH website. This led to more widespread testing, including testing of asymptomatic people, which helped lower the positivity rate.

The sharpest decline in COVID positivity is in zip codes 22302 and 22305.

When the May 7 data was reported, 22302 had a positivity rate of 26.7%, which was the second highest of the five Alexandria zip codes. By June 9, the cumulative positivity rate in 22302 had dropped to 16.1%; by July 7 it was 9.6%; and by July 21 it had fallen to 8.7%.

More dramatically, the positivity rate in zip code 22302 since June 9 is only 2.8% – the lowest in Alexandria – with 47 positive cases out of 1,700 tests conducted.

A likely explanation for this initial surge and subsequent plunge in positivity within zip code 22302 is that three of Alexandria’s long-term care facilities are located within this zip code, and all three had early and significant outbreaks of COVID-19 that have since subsided. The outbreaks in all three facilities are pending closure, which according to the VDH website means that no new cases have been reported within those facilities in the last 28 days.

There has been a drastic turnaround in zip code 22305’s positivity rate. Despite an initial positivity rate of 55.4% reported in the May 7 data, zip code 22305’s rate has plummeted to 6% positive on test results received since June 9.

Perhaps not surprisingly, the zip codes in Alexandria that have had the fewest COVID-19 tests conducted per 1,000 residents also have the fewest confirmed cases per 1,000 residents.

Zip code 22314, which includes Old Town, has both the fewest positive cases per 1,000 tests in the city, 4.5, and also the lowest number of tests conducted per 1,000 residents – 54.2. Likewise, zip code 22301, which includes the Rosemont and Del Ray neighborhoods, has 5.9 positive cases per 1,000 residents and 72.9 tests per 1,000 residents.

Conversely, zip code 22305 has had the most tests per resident in Alexandria, with 150 tests per 1,000 residents, and also by far the city’s highest number of confirmed cases per resident, with 36.9 confirmed cases per 1,000 residents.

Zip code 22302 has had the second highest test rate per resident, with 130.3 tests performed per 1,000 residents and 12.5 confirmed cases per 1,000 residents. Zip code 22304 has the second highest rate of confirmed cases per 1,000 residents in Alexandria, with 13.1, and has had 90.2 tests conducted per 1,000 residents.

A concerted effort has been made to conduct testing in all three of these zip codes.

The Virginia National Guard partnered with the VDH to conduct testing in all LTCFs that wanted it, and, according to City Spokesperson Craig Fifer, all but one LTCF in Alexandria received this point prevalence testing. This means extensive testing has been conducted at least once in either two or all three of the LTCFs in zip code 22302. Participating LTCFs were not identified by name.

In addition, VDH and the City of Alexandria partnered with Neighborhood Health, which provides health services in low-income communities, to hold several free testing clinics in zip codes 22305 and 22304, which partially explains their higher rate of testing.