More Testing Needed So Policy Makers Can Make Rational Decisions
Right now, sample collection kit shortages in the United States mean that Covid-19 testing has rightly been focused on the most severe symptomatic patients. But this is skewing our understanding of the virus and its true risks. And policy decisions that will have tremendous consequences are being made based on this incomplete data.
The Diamond Princess Case Study
An outbreak of Covid-19 on the Diamond Princess cruise ship was started by a single symptomatic passenger from Hong Kong who boarded the boat on January 20. He disembarked on January 25, and tested positive for the virus on February 1. This led to a quarantine of approximately 3,700 passengers and crew that began on February 3, 2020, and lasted for nearly four weeks at the Port of Yokohama, Japan. During the “quarantine,” the crew continued to prepare and deliver food, and health workers moved throughout the ship.
The Diamond Princess offers a real-life controlled experiment where 100% of passengers and crew were tested. It has everything all the other Covid-19 stats are currently lacking in order to accurately estimate the fatality rate for Covid-19: an undisputable numerator (10 deaths) and a complete 100% accounted for denominator (712 positive cases). The Diamond Princess provides a worst-case scenario where basically a bunch of older people were trapped in a large container with the virus for a month.
Here’s what the data from the Diamond Princess showed:
- A total of 3,711 people were onboard (1,045 crew/2,666 passengers)
- The overall median age was 58 and 33% were 70 or older.
- Most of the passengers were from Japan (1,281) and the United States (416).
- Most of the crew was from Philippines (531) and India (132).
- 712 people (19.2%) tested positive for Covid-19, including 567 passengers and 145 crew members.
- About half (46.5%) of those who tested positive showed no symptoms at their time of testing.
- Ten people died from Covid-19.
- All deaths were among passengers age 70 or older.
- The case fatality rate was 1.4% (10 deaths/712 cases).
The Diamond Princess case study stands in sharp contrast to initial reports from the World Health Organization which wildly overestimated the global case fatality rate of Covid-19 to be 3.4%.
Applying the Diamond Princess’s infection rate of 19.2% and case fatality rate of 1.4% across the entire U.S. population of 330 million would lead to estimates of 63.4 million cases and 887,600 deaths.
However, the median age of passengers and crew on the Diamond Princess (58) was about 20 years higher than the median age of the U.S. population (38).
After adjusting for the age difference, John Ioannidis, MD, an epidemiologist and biostatistician at Stanford University, has calculated that a reasonable estimate for the fatality ratio in the general U.S. population falls in a range of 0.05% to 1%.
In a March 17 opinion piece for STAT, Ioannidis said that the huge range in potential case fatality ratios markedly affects how severe the pandemic is and what should be done. “A population-wide case fatality rate of 0.05% is lower than seasonal influenza [0.1%]. If that is the true rate, locking down the world with potentially tremendous social and financial consequences may be totally irrational.”
Ioannidis said that testing for Covid-19 should be conducted in a random sample of the population and repeated at regular time intervals to estimate the incidence of new infections. In the absence of data, prepare-for-the-worst reasoning leads to extreme measures of social distancing and lockdowns that may or may not work. “If we decide to jump off the cliff, we need some data to inform us about the rationale of such an action and the chances of landing somewhere safe,” wrote Ioannidis.