Question: Last week you described measures we would observe to see if our social distancing was working. Now that a week has passed, what do those indicators show?
Answer: Thanks for remembering! In my opinion, it’s still too early to tell whether social distancing is working. But since we have more data now, let’s take a look! Back in the Q&A of 3/25, I described three indicators we should be tracking to understand how successful we’ve been in containing the epidemic. Those measures are:
- Number of patients hospitalized (daily, weekly, cumulative) [Update: I originally wrote admissions, but I think daily hospitalized patients is a better measure]
- Number of ICU patients (daily, weekly, cumulative); [Update: I originally wrote admissions, but I think daily ICU patients is a better measure]
- Number of deaths (daily, weekly, cumulative)
Thanks to Governor Cuomo’s daily press briefings, we have these data points for New York. First, looking at Figure 1,we see that the number of hospitalized patients, ICU patients, and deaths continues to increase on a daily basis and has increased unabated since reporting began earlier this month. That’s bad news, but it is not unexpected news.
Figure 1. Daily Number of New York Hospitalized Patients, ICU Patients and Deaths Continues to Increase.
Now look at Figure 2, which shows the rate of increase in hospitalizations. Good news! The growth rate (e.g. doubling time) has slowed since March 27th. This is an indication that social distancing measures — put into place state-wide on March 18th (educational facilities closed), March 20th (non-essential biz closed), and March 22nd (mandatory stay-home order) — seem to be working. If these trends hold, it means that we are slowing the pace of the epidemic. All that said, I’m still not sure how much I’d hang my hat on that assessment. Based on findings from China (described in Q&A of 3/29), we expect folks to know they are sick within about 5 days of infection and to seek medical treatment (hospitalized care) within 7–13 days of symptom onset. So, presumably, we’d start seeing growth rate in hospitalizations begin to slow about 15 days after social distancing begins. If we start the clock at March 18, then we wouldn’t expect to see growth rates in hospitalizations slow until on/about April 2nd, and that’s a pretty early estimate.
Figure 2. The rate of increase in hospitalizations has slowed; doubling time is now estimated to be 6 days rather than 3.
Now, if we look at New York’s deaths in a cumulative way (rather than daily as is shown in Figure 1 above), we see that the increase continues along an exponential trend — per Figure 3, look at that steep slope since late March! 😞 Institute for Health Metrics and Evaluation’s COVID-19 model estimates that New York won’t hit it’s peak daily number of deaths for another 8 days. And if we look at crude mortality rates over time, we find them getting worse (Figure 4), which is obviously not a good sign.
Figure 3. Cumulative COVID-19 Deaths in New York are Increasing at an Exponential Rate, totaling 2,372 as of April 2nd.
Figure 4. Crude Mortality Rate in New York State Seems to be Worsening. Today it is 2.6%.
Finally, looking at how New York data compare with the data coming out of China, per the WHO report, we find that clinical outcomes are quite similar. [Note: Given how limited testing is in other areas of the US, I wouldn’t try this analysis on a national-level. Since NY has been doing such a comparatively good job of expanded testing, it offers a good opportunity to check.] Among positive cases in New York, about 20% are hospitalized (as of April 2, 92.3K total positive, 19.5K total hospitalized), which aligns with what China experienced too. Of those who are hospitalized, about 25% are in intensive care. Put another way, about 5% of all cases in New York thus far have required intensive care. And as to mortality rates, we’re finding a crude rate of approximately 2%. All of this aligns with China’s data. But if the trend in crude death rate continues, we will be worse off than China — either a reflection of fewer tests conducted among folks with minor illness, a reflection of a faltering health health system, or a combination thereof.