More than half of U.S. states will have to significantly step up their Covid-19 testing to even consider starting to relax stay-at-home orders after May 1, according to a new analysis by the Harvard Global Health Institute and STAT.
As Sharon Begley writes in STAT, the joint analysis shows that as the U.S. tries to move beyond its months-long coronavirus testing debacle — faulty tests, shortages of tests, and guidelines that excluded many people who should have been tested to mitigate the outbreak — it is at risk of fumbling the next challenge: testing enough people to determine which cities and states can safely reopen and stay open. Doing so will require the ability to catch reappearances of the coronavirus before it again spreads uncontrollably.
Population: Population of the state in millions of people. Taken from American Community Survey data
May 15 Deaths: Obtained from Los Alamos National Labs COVID-19 Forecasts on April 15, 2020.
May 1 Cases: Number of new COVID-19 Cases on May 1. Calculated as 100 * May 15 Deaths. Based on a 2-week period from infection to death and a 1% Infection Fatality Rate. Estimates of Infection Fatality Rates vary significantly but many estimates now converge around 1%.
May 1 Symptomatic Cases: Number of new symptomatic COVID-19 Cases on May 1. Calculated as 0.75 * May 1 Cases. This is based on CDC estimates that 25% of COVID-19 cases are asymptomatic.
May 1 Contacts: Number of contacts to test based on new infections on May 1. Calculated as 10 * May 1 Symptomatic Cases. We assume that we will initially test all symptomatic people thus we will only identify symptomatic cases and thus only will trace contacts for symptomatic cases. Estimates of number of contacts vary widely but given some measure of continued social distancing it has been estimated at an average of 10 contacts per infected individual.
Other Influenza Cases on May 1: How many non-COVID symptomatic cases we expect to see on May 1. In previous years, CDC Historical Influenza Surveillance found that in early May on average, 1.7% of provider visits were for Influenza-Like Illness (ILI). The CDC also reports 883.7 million provider visits per year. Dividing these by 365 and multiply by 1.7% we find about 40,000 ILI cases per day. We then divide these across states proportionally by population.
Total Tests (Contact Tracing and Isolation): Estimated number of tests needed given a strategy of testing all symptomatic individuals and contacts of those with positive tests. Calculated as the sum of May 1 Symptomatic Cases, May 1 Contacts, and Other Influenza Cases on May 1
Total Tests (10% Positive Rate): Estimated number of tests given a strategy of reducing the positive rate of testing below 10%. Calculated as 10 * May 1 Cases. A 10% positive rate or below is the goal provided by the WHO; other experts have shown that a positive rate above 10% suggests inadequate testing.
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