Lessons to tackle Covid from a cruise ship
NEWDELHI: More than half the 17% of people who were diagnosed with coronavirus disease (Covid-19) on board the cruise ship Diamond Princess were asymptomatic, indicating that a large number of infected people may be undetected, and consequently suggesting that the fatality rate of the disease may be lower than the current global estimate, according to researchers analysing data from what was until last month the site of the biggest outbreak outside China.
A total of 712 cases and seven deaths were reported from the Diamond Princess in February.
Testing and tracking all confirmed cases on board the Diamond Princess is giving invaluable clues about asymptomatic cases, fatality rate, and the benefits of quarantine to enforce social isolation, according to a yet-to-be-reviewed study by Eurosurveillance (Europe’s journal on infectious disease surveillance, epidemiology, prevention and control), the paper published in biomedical preprint server medrxiv.
The ship has become a giant petri dish for researchers to observe exposure, risks, death rate and symptoms (or the absence of them) in 3,711 passengers and crew members, of which around 3,000 were tested, some of them twice, and each death or recovery was mapped.
The study estimated that the infection fatality rate on the ship was around 1.3% (ratio of death of all infections, followed till they recovered or died), which is much lower than the 3.8% case fatality rate (NCFR, or ratio of reported deaths to reported cases to date) estimated by the
World Health Organization, which reached its initial estimate by dividing China’s total number of deaths by the total number of confirmed cases. According to the WHO’S formula, the NCFR would now be 4.6%.
“The case fatality rates are variably reported in various studies to be between 1% and 3%, so probably it’s somewhere around 2%. It’s lower in countries where effective measures have been taken early on, as in South Korea, where it’s 0.6% mortality. So I’d say it’s between 1% and 2%, if adequate public health measures are taken,” said Dr K. Srinath Reddy, president, Public Health Foundation of India.
The Euromonitor study also combined the ship’s data with at least 72,000 confirmed cases in China put the estimated the death rate in China to be around 0.5%.
Since the average age on board the ship was 58, the researches believe this indicates that the number of asymptomatic carriers of the infection in the younger general population is likely to be higher than some other studies have suggested.
Since the Diamond Princess, at least 25 other smaller cruise ships have confirmed Covid-19 cases, including 78 cases on the Grand Princess, which was quarantined off the coast of California.
The study underlined that social isolation as a public health strategy. The day the quarantine was introduced, one person could to infect around seven others because of the confined space and high surface contamination, but after room quarantining was introduced on February 3, the average number people who got infected from one infected case fell under one.
“India has stepped up testing, but a lot more surveillance needs to be done to get the true picture of the epidemic in India, including in underserved and rural areas,” Dr N. K. Ganguly, former director general of the Indian Council of Medical Research.