Figure 1. Santa Fe County: The cumulative number of positive COVID-19 test results is shown by NMDOH reporting date. The green curve is our estimate of the current number of active COVID-19 cases (among individuals that initially tested positive). Also presented is the doubling time computed from the data. The doubling time is calculated for a given day by using data from two days earlier and two days later. An exponential function is drawn through the doubling time to emphasize the nature of the increase beginning March 27. Created by Marv Alme

Figure 2. 30 Counties of New Mexico: The cumulative number of positive COVID-19 test results is shown by NMDOH reporting date. The green curve is our estimate of the current number of active COVID-19 cases (among individuals that initially tested positive). Also presented is the doubling times computed from the data. The doubling time was calculated by using data from two days earlier and two days later. Created by Marv Alme

By MARV ALME
Los Alamos

While the enormous tragedy in the Pueblos and Reservations of Northwest New Mexico has intensified during the past week, Santa Fe County continues its overall success story despite adding 10 positive tests in the three days from April 20-22.  

In the last four days, only two positive tests have been added.

Figure 1 above shows the cumulative number of positive COVID-19 test results reported by NMDOH, and the doubling time for that data. The doubling time for a given day has been computed using the data from two days before and two days after. We also show our estimate of the current number of active COVID-19 cases among the individuals who tested positive. 

This estimate is generated by subtracting the number of positive tests reported ten or more days ago from the cumulative number of positive tests reported to date. We are working to improve this simple estimate but if we apply this estimate to the totals for all of New Mexico, we find it instructive that the ratio of hospitalizations to active cases has varied little from 10% until the last two days. 

In the analysis we presented a week ago, we made an error in attributing the rollover in the estimated number of active COVID-19 cases in Santa Fe to the doubling time becoming longer than 10 days. For any fixed doubling time, the number of active cases will increase almost exponentially, and this is what is happening during the last week in the 30 counties of New Mexico with McKinley, Sandoval and San Juan removed, as we will discuss below. 

What actually rolled the estimated number of Santa Fe County active cases over was that from March 27 to April 13, the doubling time increased exponentially! Figure 1 above shows an exponential function that we simply drew through the March 27 and April 13 data points.

Now turning to the 30 counties of New Mexico, Figure 2 above shows the cumulative number of positive tests in the 30 counties as well as the total for all of New Mexico. Also shown is the doubling time and our estimate of the number of active COVID-19 cases. As was the case for Santa Fe County, the estimated number of active cases peaked and began to decrease because of the sharp increase in doubling time that began on April 8. After peaking at 22 days, it has varied between 17 days and 20 days. This means that the number of active cases will continue to increase throughout the state.