Much of the current discourse on — and dismissal of — the Covid-19 outbreak focuses on comparisons of the total case load and total deaths with those caused by seasonal influenza. But these comparisons can be deceiving, especially in the early stages of an exponential curve as a novel virus tears through an immunologically naïve population.

Perhaps more important is the disproportionate number of severe Covid-19 cases, many requiring hospitalization or weekslong ICU stays. What does an avalanche of uncharacteristically severe respiratory viral illness cases mean for our health care system? How much excess capacity currently exists, and how quickly could Covid-19 cases saturate and overwhelm the number of available hospital beds, face masks, and other resources?

This threat to the health care system as a whole poses the greatest challenge.

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As I initially described in a Twitter thread, simple mathematics can derive rough estimates for how this might play out.

This exercise can inform our level of urgency and equip us to anticipate non-obvious, second-order effects, some of which can be mitigated with proper preparation.

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As of March 8, about 500 cases of Covid-19 had been diagnosed in the U.S. Given the substantial underdiagnosis at present due to limitations in testing for the coronavirus, let’s say there are 2,000 current cases, a conservative starting bet.

We can expect a doubling of cases every six days, according to several epidemiological studies. Confirmed cases may appear to rise faster (or slower) in the short term as diagnostic capabilities are ramped up (or not), but this is how fast we can expect actual new cases to rise in the absence of substantial mitigation measures.

That means we are looking at about 1 million U.S. cases by the end of April; 2 million by May 7; 4 million by May 13; and so on.

As the health care system becomes saturated with cases, it will become increasingly difficult to detect, track, and contain new transmission chains. In the absence of extreme interventions like those implemented in China, this trend likely won’t slow significantly until hitting at least 1% of the population, or about 3.3 million Americans.

What does a case load of this size mean for health care system? That’s a big question, but just two facets — hospital beds and masks — can gauge how Covid-19 will affect resources.

The U.S. has about 2.8 hospital beds per 1,000 people (South Korea and Japan, two countries that have seemingly thwarted the exponential case growth trajectory, have more than 12 hospital beds per 1,000 people; even China has 4.3 per 1,000). With a population of 330 million, this is about 1 million hospital beds. At any given time, about 68% of them are occupied. That leaves about 300,000 beds available nationwide.

The majority of people with Covid-19 can be managed at home. But among 44,000 cases in China, about 15% required hospitalization and 5% ended up in critical care. In Italy, the statistics so far are even more dismal: More than half of infected individuals require hospitalization and about 10% need treatment in the ICU.

For this exercise, I’m conservatively assuming that only 10% of cases warrant hospitalization, in part because the U.S. population is younger than Italy’s, and has lower rates of smoking — which may compromise lung health and contribute to poorer prognosis — than both Italy and China. Yet the U.S. also has high rates of chronic conditions like cardiovascular disease and diabetes, which are also associated with the severity of Covid-19.

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At a 10% hospitalization rate, all hospital beds in the U.S. will be filled by about May 10. And with many patients requiring weeks of care, turnover will slow to a crawl as beds fill with Covid-19 patients.

If I’m wrong by a factor of two regarding the fraction of severe cases, that only changes the timeline of bed saturation by six days (one doubling time) in either direction. If 20% of cases require hospitalization, we run out of beds by about May 4. If only 5% of cases require it, we can make it until about May 16, and a 2.5% rate gets us to May 22.

But this presumes there is no uptick in demand for beds from non-Covid-19 causes, a dubious presumption. As the health care system becomes increasingly burdened and prescription medication shortages kick in, people with chronic conditions that are normally well-managed may find themselves slipping into states of medical distress requiring hospitalization and even intensive care. For the sake of this exercise, though, let’s assume that all other causes of hospitalization remain constant.

Let me now turn to masks. The U.S. has a national stockpile of 12 million N95 masks and 30 million surgical masks for a health care workforce of about 18 million. As Covid-19 cases saturate nearly every state and county, virtually all health care workers will be expected to wear masks. If only 6 million of them are working on any given day (certainly an underestimate) they would burn through the national N95 stockpile in two days if each worker only got one mask per day, which is neither sanitary nor pragmatic.

It’s unlikely we’d be able to ramp up domestic production or importation of new masks to keep pace with this level of demand, especially since most countries will be simultaneously experiencing the same crises and shortages.

Shortages of these two resources — beds and masks — don’t stand in isolation but compound each other’s severity. Even with full personal protective equipment, health care workers are becoming infected while treating patients with Covid-19. As masks become a scarce resource, doctors and nurses will start dropping from the workforce for weeks at a time, leading to profound staffing shortages that further compound the challenges.

The same analysis applied to thousands of medical devices, supplies, and services — from complex equipment like ventilators or extracorporeal membrane oxygenation devices to hospital staples like saline drip bags — shows how these limitations compound one another while reducing the number of options available to clinicians.

Importantly — and I cannot stress this enough — even if some of the core assumptions I’m making, like the fraction of severe cases or the number of current cases, are off even by several-fold, it changes the overall timeline only by days or weeks.

Unwarranted panic does no one any good, but neither does ill-informed complacency. It’s inappropriate to assuage the public with misleading comparisons to the seasonal flu or by assuring people that there’s “only” a 2% fatality rate. The fraction of cases that are severe really sets Covid-19 apart from more familiar respiratory illnesses, compounded by the fact that it’s whipping through a population without natural immune protection at lightning speed.

Individuals and governments seem not to be fully grasping the magnitude and near-inevitability of the national and global systemic burden we’re facing. We’re witnessing the abject refusal of many countries to adequately respond or prepare. Even if the risk of death for healthy individuals is very low, it’s insensible to mock decisions like canceling events, closing workplaces, or stocking up on prescription medications as panicked overreaction. These measures are the bare minimum we should be doing to try to shift the peak — to slow the rise in cases so health care systems are less overwhelmed.

The doubling time will naturally start to slow once a sizable fraction of the population has been infected due to the emergence of herd immunity and a dwindling susceptible population. And yes, societal measures like closing schools, implementing work-from-home policies, and canceling events may start to slow the spread before reaching infection saturation.

But considering that the scenarios described earlier — overflowing hospitals, mask shortages, infected health care workers — manifest when infections reach a mere 1% of the U.S. population, these interventions can only marginally slow the rate at which our health care system becomes swamped. They are unlikely to prevent overload altogether, at least in the absence of exceedingly swift and austere measures.

Each passing day is a missed opportunity to mitigate the wave of severe cases that we know is coming, and the lack of widespread surveillance testing is simply unacceptable. The best time to act is already in the past. The second-best time is right now.

Liz Specht is the associate director of science and technology at The Good Food Institute.

  • the good news is this is already old information… we have implemented strict social distancing controls, while voluntary… they will work if people follow them. further, while testing will be critical, the most important step is to blunt the spread. to do that means that you stay home… period. healthy or not… stay home… read a book.

  • In the two plus months since the first reported Covid19 death in China, that country has reported just over 80,000 confirmed cases. Even if you assume Chinese state media is only reporting half of the exact number, you’re only at 160k cases. But we’re to assume that the US will have 3 million cases in the same ~ 2 month time frame? Yes China is an autocratic state that can simply mandate prevention measures, but they also have a population density more than 3 time greater than the US. I’m just not sure how you can assume a case rate 18 times higher in the US (and that’s assuming China has double the reported confirmed cases) than China has shown in a similar time frame.

    • It’s because China (also South Korea, a democratic nation) is actually on the ball when testing people and enforcing quarantine. We delayed testing by a MONTH for a virus that spreads exponentially, and quarantine is only now being instituted piecemeal. If quarantine laws are lax and you don’t know who’s sick, there’s going to be much higher rates of presymptomatic spread, and as a result you’re gonna have exponentially more cases and fatalities.

    • Totally agree. There is no “Simple Math” in biology. The modeling of this virus spread is not as simple as plugging numerators and denominators from China into your algebraic equations for USA. There is simply not enough data to calculate the transmission/morbidity/mortality rates in our population (which will be different from China, different from Italy, different from Japan), and the biological variables. This virus has evolved to do what it is doing in the human environment we live in, to think we can stop its spread is the hubris of Man. Wasting resources and disrupting the world in an attempt to protect everyone from getting it is insanity. Our resources and intellect should be focused on protecting the clearly defined population most at risk for dying, >70 with COPD and other comorbidities. Isolate them, screen interactions, provide support at home, and let the virus run its natural course through the healthy population. In the face of no vaccine or antiviral treatment the only way to alter the course of transmission is through naturally acquired “herd immunity” that will create “back burns” to slow the ranging forest fire of this pandemic. That alone will flatten the curve of hospitalization rates.

    • Good point. China apparently stabilized their case load at 0.006% of the population, yet you expect it to reach 1% of US population. Do you attribute that difference entirely to their “extreme measures”, or are you making some incorrect assumptions about the rate of spread of Covid 19?

    • China was 15-30 days behind the curve because they didn’t even know what it was and they were slow to intervene. Plus it started in a metro area of 11 million, so I look at China as worst case scenario. Even if they are no being truthful all their graphs and percentages match up. Like stated, if they had double the cases it’s still only 162,000 total with it widespread in a city of 11 million. New York is only 8 million and we knew it was coming and what it was. But 2 million people are going to get sick here, that just doesn’t make any sense.

  • This is the most comprehensive yet fairly easy to understand explanation I’ve read. As retired healthcare trainer people have a hard time understanding and believing if you tell people the truth (we don’t have enough supplies, etc.) They are much more likely to comply with requests. In your scenario the fact that we don’t currently have enough tests does not even play into why people need to act now (stay home and/or distance).

    Thank you
    Dk

  • Assume there are, at peak, 5 million cases in the USA (30 states with >100000 and 20 states with an assortment of numbers of cases) and of that 5 million cases, 40 percent are high risk (immune compromised or elderly 60 and above). Assume that 1% of these, within the following two weeks are in desperate need of ventilators at any time. This means that 1% of 2 million or about 20,000 ventilators will be needed. That is a realistic number to shoot for. When things are out of reasonable capacity to produce is if the peak is 10 times 5 million (or like a typical flu pandemic). with a 6 day doubling time if the number is 5 million now, 10 million in 6 days, 20 million in 12 days, 40 million in 18 days – is the expected growth of cases. That is why the next 15-18 days we must do our best to keep the growth (doubling) rate down and flatten the curve! With an Ro of 2.0, COVID-19 only takes 28 doubling cycles to reach 75% of our population, unchecked.

  • I think you math estimation is inaccurate because you assume all ages have the same hospitalization rate. Your calculations have to consiser age. So you instead of 10% hospitalization rate, you need tk weight hospitalization by age.

  • Why run the numbers with no mitigating measures? This is a classic example of “dumb” statistics. You’re not describing what actually happens, you’re larding rhetoric with output from a calculator.

    • You run the numbers with no mitigating measures to show what will likely happen with no mitigating measures. And it is not pretty. That is the point. That is the best logic that leads a person to see that mitigating measures are necessary.

  • I read your article and am keeping it on my computer to read again…being 90 years old, I may need a reminder. Although, I must say, thus far my mind seems fine. I don’t go out into the ‘public’ areas that much anymore, but, my husband does and so does my son and his wife (whose home where we have a small apartment). I would they would abide by the rules/suggestions we’ve all read.
    Seems it is always something and the ‘issues’ seem to get worse all the time. Perhaps it’s because the world population is toooo big/huge and not all human beings do the sensible things to protect themselves nor do the even think of the consequences of their actions on others. “That’s Life, that’s what the people say.” I said that for years and when my daughter was younger, she hated it. Actually, it’s from a song from my past.
    It seems as the world population increases, there are more problems and illness. You’d think, as the world ages and people learn more, that things would be better health wise. The do in some instances BUT, more people, crowding etc. it just gets harder, regardless of many medical improvements.
    Take care of one thing and another problem pops up.
    Thank you for the opportunity to give my opinion and for ‘chewing your ears off” OR should I say ‘contributing to boring you’ NAN VANT………..ETC.

  • There are several other factors that need considered. The epidemic spread more quickly in China, S. Korea, and Italy probably due to population density. Also we may be less affected as we have a higher ratio of seniors living independently, unlike other countries. Lastly, we should (or rather hope) survive this epidemic better as we had warning and time to prepare- something China didn’t have. There have only been 218 new cases reported in China (https://ourworldindata.org/coronavirus) in the last 7 days, so this epidemic has a life span of 5-6 weeks. Stay healthy, maintain hygiene, and help your neighbors (whatever ways you can). Have faith and keep a level head, and we can all weather this storm.

  • Best indicator is Wuhan. A city of approx 10 million where the epidemic lasted approx 3 months. Under 1% were tested positive (ie came through the medical system through hospitals) although likely many times that number had mild infections. 60,000 were treated in hospitals (Some in makeshift field hospitals such as converted convention halls/gymnasium etc) 10,000 were treated in critical care with additional critical care capacity added through 30 new 15 bed units being created and adapting of existing – so several thousand.
    So these are the models we need to adapt to big city centres like NY, SF, Seattle etc… The real US problem is that the healthcare is fragmentary and private….

  • Don’t we need to factor in the way this disease attacks the elderly vs the young and youngish? If we take the fairly simple step of isolating the elderly to keep them from exposure, don’t we drastically reduce the number of hospitalizations caused by COVID19? The article claims a hospitalization rate of 10% (that seems way too high). What is the rate of hospitalization for those under 60 years old? I can’t find that data, but based on the mortality rate for people under 60, I would guess the hospitalization rate would be much, much lower. So low it might not even burden the healthcare system. If we isolate only the elderly, as opposed to the entire population, does that solve the problem of overwhelming hospitals?

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