Fairfax County is part of Northern Virginia and is the most populated county in the state by far, with over 1.1 million people. This analysis focuses on the data related to the COVID-19 pandemic, specifically in Fairfax. The county has a decent website with a dashboard for case data in the Fairfax Heath District, which encompasses the county and the small, embedded localities of Fairfax City and Falls Church. However, most of that data is aggregated over the entire duration of the pandemic (since March 2020). I’m more interested in what is happening now, as well as trends over time.

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We use data from the Virginia Department of Health . The source data was downloaded from the Virginia Department of Health website and is as of September 29, 2022.

Cases and Hospitalizations

These charts show the 5-day moving average for both reported cases and hospitalizations in the Fairfax Health District. At times these data points appear to drop below zero. This is likely due to corrections made in the source data. For example, on September 11, 2021, the cumulative number of hospitalizations in Fairfax County dropped by 30 from the previous day and that causes the chart of the 5-day average of hospitalizations to dip below zero for a few days.

On November 23, 2021, Fairfax County had a major adjustment to the number of hospitalizations considered related to COVID-19, reducing the cumulative count up to that date by 206. This is equivalent to almost 15% fewer hospitalizations in 2021 than previously reported.

Starting March 1, 2022, the Fairfax County Health Department was “reviewing COVID-19 hospitalization data as part of its ongoing data review process”, per its website COVID-19 Case Data for Fairfax Health District. Through that process they expected an increase in total hospitalizations but note that the additions represent older hospitalizations that occurred prior to January 8, 2022.

This practice of updating hospitalization data on the current date instead of the date of hospitalization frustrates the ability to understand temporal trends in the hospitalization data.

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This is what the hospitalizations chart looks like if you remove the artificial dips caused by the data quality adjustments.

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Hospitalization Rate

The following chart shows the 5-day average for the hospitalization rate in Fairfax since the start of the pandemic. The hospitalization rate is the ratio of hospitalizations to positive cases reported each day. The blog post Estimating COVID-19 Case Counts discusses using the hospitalization rate to estimate the true number of COVID-19 cases early in the pandemic, when testing was very limited and thus the number of cases was likely under-counted.

Note that when the number of cases and hospitalizations are extremely low , like it was in early June 2021, the rates of hospitalization can seem alarmingly high. But in reality, a 25% hospitalization rate is just 1 hospitalization and 4 reported cases. Also, note that the sequence of reporting of cases and hospitalization is not at the person level. So in the example, the single hospitalization was not of one of the cases reported that day, but instead someone whose case was reported previously.

The following charts are adjusted to prevent the rate from falling below zero when the occasional data quality adjustments are made, as discussed above. In those cases, there are gaps in the trend lines.

The average hospitalization rate in Fairfax over past month was 0.014.

The average hospitalization rate in Fairfax over the past two months was 0.013.

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Daily Cases, Past 4 Weeks

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Weekly Change

The chart below shows the total number of cases per week, Sunday to Saturday, in Fairfax. The dates are each Sunday, the first day of the week for that case count.

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Cases by Zip Code

Fairfax is made up of over 40 zip codes. This map shows the total number of new c