Coronavirus cases cross one million without counting asymptomatic ones

Coronavirus - 1-Optimized

On April 2, novel coronavirus (SARS-CoV-2) cases crossed one million and deaths passed 50,000. Besides missing out people with mild symptoms and underreporting, the actual number of infected people will be manifold higher as most countries do not test people who are asymptomatic.

On April 2, the number of people infected with novel coronavirus (SARS-CoV-2) in 181 countries/regions crossed one million and deaths passed 50,000. On April 3, the total number of cases and deaths stands at 10,39,166 and 55,092, respectively.

With 2,45,646 cases, the U.S accounts for 24% of the global total, while Italy with 13,915 deaths has over 26% of total mortality. Four countries — the U.S., Italy, Spain and Germany have more cases reported than China.

Exponential increase

The exponential increase in number becomes striking considering that the time taken to report 1,00,000 more cases has been reducing. If it took 12 days to double to 2,00,000, it took just three days each to cross 0.3 and 0.4 million. Thereafter, 0.1 million more cases have been reported every two days except on two occasions — increase from 0.6 million to 0.7 million and 0.9 million to 1 million happened in a single day.

Yet, the cases reported so far might be a small percentage of the actual numbers in most countries. The main limiting factor in knowing the true spread has been the restricted number of tests carried out in most countries, India included.

In about a month after restrictions on testing were loosened, the number of tests carried out in the U.S. crossed one million on March 30. While this may be a huge number, there is still a bottleneck in the number of people being tested. According to The Washington Post, as on March 28, only 2,250 tests per million were performed, which is two-thirds of what South Korea did three weeks earlier.

Missing cases

Besides missing out people exhibiting mild symptoms and underreporting by countries, the actual number of people infected by the virus might be manifold higher as no attempts have been made by most countries to test people who do not show symptoms. There is accumulating evidence suggesting that a “substantial fraction” of people infected with the virus are asymptomatic.

For instance, in South Korea, more than 20% of asymptomatic cases did not develop symptoms during hospitalisation. If in Italy the virus was spreading silently for about 50 days before the first case was reported on February 20, in Iceland, nearly half of the 20% who tested positive for the virus were either asymptomatic or showed only mild symptoms.

43,000 asymptomatic cases not reported

The South China Morning Post said more than 43,000 people in China who tested positive by end February were asymptomatic and not reported. Since April 1, China has been reporting new cases that are asymptomatic. China’s National Health Commission reports that as on March 31 there have been 1,541 asymptomatic cases.

The World Health Organization maintains that the virus mainly spreads through droplets and contact with contaminated surfaces, and the risk of getting infected by an asymptomatic person is “very low”. But more experts are now beginning to consider asymptomatic cases as an important source of virus transmission.

The evidence once again underscores why India should begin aggressive testing to know the extent of community spread. Mitigation measures alone without aggressive community testing run the risk of continued spread once the lockdown is withdrawn.

Published in The Hindu on April 4, 2020