Introducing Coronavirus III

Similar to SARS and MERS, the current Chinese Coronavirus, known as 2019-nCoV, is transmitted from person to person by close personal contact. It is also believed to be readily transmitted by respiratory droplets and aerosols produced when an infected person coughs or sneezes. The CDC informs us that the Chinese epidemic “reportedly had some link to a large seafood and animal market, suggesting animal-to-person spread.” Some believe 2019-nCoV might be a Chinese bioweapon which leaked out of their Wuhan BSL-4 microbiology research laboratory.

Exponential expansion of an infectious disease occurs when the rate of growth is proportional to the number of people currently infected. The mathematical formula for exponential growth is:

xt = x0 (1+r)t

“xt” refers to the total number of cases, “xo” the number of index cases or the number of cases at the time of mathematical calculation, “r” the rate of disease transmission (the number of people infected by each prior case), and “t” the number of incubation time intervals during the course of an epidemic. Since patients don’t easily transmit the virus after recovery or death, the equation should reduce closer to x t = x 0 (r)t.

This graph demonstrates the exponential expansion of 2019-nCoV, as of 1/27/20, using data from the Chinese government:

How Contageous Is The New Virus?

In the current 2019-nCoV epidemic “r” has been estimated by an international team of university researchers to be 3.8, and the best estimate for incubation time is 4-5 days which occurred in earlier Coronavirus epidemics known as SARS and MERS. Read et al. have estimated only 5% of Chinese cases have been detected and reported. In assuming 3 out of 4 cases remain in the incubation period, asymptomatic, but still contagious toward the end of incubation, the current number of cases could be 31,200 rather than the 7,800 currently acknowledged by the Chinese government. Are they counting 2019-nCoV cases with pneumonia as simply pneumonia, placing artificial limits on diagnostic testing, and lying about the mortality rate?

Huang et al., reporting in The Lancet on a cohort of 41 Wuhan nCoV patients, observed that all developed bilateral pneumonia, 32% required admission to the intensive care unit, 29% developed respiratory distress, 12% developed ischemic cardiac injury, 10% required intubation and mechanical ventilation, and 15% died. Read et al. have mathematically predicted about 200,000 cases in China by February 4 using an estimate of 11,341 cases on January 21 and an “r” of 3.8. Using a more conservative “r” of 3.0, an incubation time of 5 days (for contagiousness rather than for symptoms), and a current number of 31,200 cases (23,400 undetected and unreported) there would be 281,000 cases by February 9 and about 68 million cases by the first week of March. The CDC confirmed the Coronavirus’ “first known case of person-to-person spread” in the US. It happened between spouses in Chicago after the wife returned from China.

Fatality Rates

Chinese government data indicate a 2.3% mortality, but using the 15% fatality rate observed by Huang et al., and realizing the absence of a Coronavirus vaccine, there could be nearly 7 million deaths by March. Gabriel Leung, Dean of Hong Kong School of Medicine, recently estimated that there are about 44,000 cases of 2019-nCoV in Wuhan, China (26,000 active, the rest in incubation). If this is true, we could expect to see up to 100 million cases in China by March and 15 million deaths.

These numbers are extremely disturbing, but depend upon the accuracy of current estimates for disease transmission, incubation time, mortality rate, and an accurate appraisal of unreported cases. The case numbers could be reduced with strict quarantines and travel restrictions if the mortality rate is less than 15%, the “r” value is less than 3.0, or the incubation time greater than 5. Of course, the numbers might be higher if the Chinese government is underreporting its cases, the “r” value is greater than 3, the incubation time is less than 5, or if the mortality rate is closer to 35% as seen in MERS.

Just A Cold Or Emergency?

If these estimates are accurate, or even in the right ballpark, it would be wise to quarantine all people arriving in the United States from 2019-nCoV epidemic areas for 14-21 days, hospitalizing (in quarantined hospitals) any with signs or symptoms of 2019-nCoV. President Donald Trump should have already banned all incoming and outgoing flights with China, just as BritishAirways has done. North Korea just closed its border with China, imposing a month long quarantine for all arriving travelers, and has banned all foreign tourists.

Based on current information, it appears we should be prepared, as best we can, for a large and possibly massive epidemic. Without drastic measures to prevent their entry, people infected with 2019-nCoV are likely to enter the United States during the incubation phase of their illness, looking well and with no fever or symptoms. Unfortunately, we are vulnerable because no vaccine is currently available, and there may not be enough antiviral medication to go around.