If you've been following developments in the COVID-19 pandemic (and who hasn't?), you've probably heard the experts talk about "modeling." For the uninitiated, modeling simply means using data (the more, the better) to map contagious disease spread and predict what will happen next. George Box, a famous English statistician, once stated, "All models are wrong. Some are useful." New Mexico has developed a very useful model.
Public health officials everywhere are using models to make informed policy decisions that will effectively and consistently slow COVID-19 transmission and prevent a surge that would overwhelm our ability to care for patients. These forecasts predict demand for general hospital beds, ICU beds, and ventilators, as well as forecasting daily and cumulative deaths due to COVID-19.
The best models are based on the best data – including data unique to each state. The New Mexico model is the work of 25 experts from around the state. It includes characteristics of the virus from other countries and other parts of the U.S. and applies them to the unique population characteristics of our state. Our New Mexico model is the only one that includes county population demographics, disease burdens of populations by county, social determinants of health, supply of healthcare resources, and other variables. This is important because New Mexico has a much higher proportion of vulnerable people than almost all other states. Our team meets weekly to update the model based on new case information. The result: A robust and useful model that can be modified daily with our own data.
The model predicts two important dates for the state as a whole and for each county:
- The surge date, which is when hospitals will have insufficient resources (general beds, ICU beds, ventilators) needed to handle the surge of COVID patients at their baseline (fully staffed) capacity. This date varies by county.
- The peak date, which is when each county will see its maximal number of cases in one day and hospitals will see their maximum volume, above licensed capacity. This date also varies by county.
The model also predicts New Mexico's doubling rate — an estimation of how many days it takes for the number of coronavirus cases to double. The New Mexico model follows the epidemiologic standard, which is based on the average daily growth rate since the pandemic started here. A simpler method looks only at more recent data, and ours does show a longer doubling time. However, we're sticking with the standard because it allows us to compare how New Mexico is doing compared to other states. The really good news is that the standard doubling time has gone from 1.9 to 5.2 days. And it has taken 11 days for the case count to double since April 20.
Health Secretary Kathy Kunkel and our governor have done an incredible job rapidly ramping up testing to make New Mexico one of the leading states in this regard. But much more testing is needed, especially of vulnerable populations and in areas where testing rates are low, to further refine our model and better understand the level of COVID exposure in New Mexico.
Our evidence-based modeling assumes that for every confirmed COVID-19 case there are four additional cases in the population. However, a brouhaha erupted last weekend between statisticians when studies in San Francisco and Los Angeles suggested a ratio of 50 or greater unknown cases for each known case. (Brouhahas between statisticians are rare; statistics geeks should definitely check it out.) The number of unidentified cases, of course, has bearing on reopening strategies as it tells us there are more people with possible COVID immunity (potentially good) but also more active infections out there (definitely bad).
As we collect more data, we are using national standards to classify each element – case counts, hospitalizations, deaths and recoveries, for example.
And the best news of all from this week's model update is that we have flattened the curve! It now appears that both our surge and peak levels have decreased. Combine that with a Medical Advisory Team expansion of delivery system pandemic planning across the state that has dramatically increased the number of potential ICU beds, our most scarce resource, and it appears that we are very close to being able to provide care to everyone who needs an ICU bed for COVID-19 at our peak.
We still have significant hot spots, particularly in the northwest region of our state. We will be making more county-level modeling data available on-line very soon.
Our goal for our New Mexico model is to provide our leaders with a useful, accurate and continuously adjustable tool to help them make informed decisions to effectively and consistently slow the transmission of COVID-19. But the results we are now seeing are not due to the model itself, but rather the result of the decisions made by the vast majority of New Mexicans to stay at home and make the difficult social distancing changes in your lives that actually have already saved the lives of many of our neighbors.
Thank you for that.
By David R. Scrase, M.D.,
Secretary, Human Services Department