For every confirmed case, there can be 25 more Covid-19 infections; carriers of the virus can make thousands sick, specialists warn
MEXICO (El Universal) – Mexican scientists specializing in mathematics, statistics, and infectious diseases warned that there could be up to 25 times more cases of Covid-19 in the country than those confirmed by laboratory tests. This would mean between 881,000 and 1.27 million people infected, many without symptoms but with the capacity to infect.
The data come from estimates made by scientists consulted by EL UNIVERSAL. Alejandro Macias, considered the expert on the H1N1 epidemic in 2009, when he was the National Commissioner for the Prevention and Control of the SSA, explained that until laboratory tests are carried out to look for antibodies in people’s blood, as was done in New York, it will not be known precisely how many people were infected with Covid-19.
However, he believed that because of the size of the disease and its spread, there are currently more than 1 million people in the country infected with Covid-19.
“In Mexico, we are unlikely to have less than 1% [of people infected with coronavirus] of the national population. I don’t think it will be less and hopefully many more so that many will have antibodies. If we are 127 million people, at least 1.27 million could have already been infected in Mexico. That figure may cause some commotion, but if I say that 1 percent of the population is already infected, no one is surprised. It is the same,” the specialist added.
Arturo Erdely Ruiz, an academic from the Acatlán School of Higher Studies (FES), with level 1 membership in the National System of Researchers and a Ph.D. in Mathematics, calculated that the disease might be 23 times larger than what we know from the most recent estimate data published by the SSA on May 3.
The data is obtained by applying an expansion factor of 23 times, which means how many patients there may be for each case confirmed through laboratory testing. The estimated cases positive to Covid-19 are divided by the accumulated number of confirmed cases up to the moment this estimate was made.
By applying this expansion factor, also called the multiplication factor, to the 38,324 cases of Covid-19 reported by the Health Secretariat on Tuesday, the estimate is that 881,452 infected people in the country. Most may be carriers of the virus but may not have developed symptoms, which does not prevent them from being infected.
“That factor was initially at 31.3 times as of April 8 but had been dropping. The last time I estimated it with the information they gave until May 3, it is estimated to be around 23 times. That’s the ratio we can have between confirmed and estimated cases. Of the expected cases, the majority are mild, the minority are the serious ones that arrive at the hospitals,” the expert explained to EL UNIVERSAL.
On May 3, the SSA said 104,562 people in the country tested positive for Covid-19, according to information obtained from the Sentinel epidemiological surveillance model. This system is a kind of survey applied by the federal government to identify cases of coronavirus in 475 health monitoring units of respiratory disease. Its objective is to collect useful quality data instead of large amounts of information but of poor quality.
By dividing the 104,562 estimated cases by 4,524 confirmed instances at that time, Erdely’s multiplication factor was 23 Covid-19 estimates for each positive.
“For Mexico, I estimate as of Tuesday, with the factor I have been proposing, that we will have about 900,000 people infected, estimated total cases. There’s no need to panic. These are mild cases, some have already been cured. We are talking about the total number of infected people in Mexico that will close the year with 1.8 million,” said the mathematician.
The expansion factor can vary according to the evolution of the epidemic. Still, the SSA removed from its daily reports the data that allowed scientists to make these estimates with greater precision.
Gustavo Cruz, a member of the Institute of Applied Mathematics and Systems Research (IIMAS), explained to EL UNIVERSAL there is a sub-accounting in the number of cases, but this is a reality that occurs worldwide, where the expansion or multiplication factor of cases has reached up to 50%, which can also occur in Mexico.
“We calculate the expansion factor for the number of infected people between 50 and 80, but I insist that the number is vast because [it includes] people who are infected and who will never have symptoms, never realizing they had the disease,” he said. “The numbers that governments get are only from the people who come to health services. For every one of these, there are about 50 who never make it to the health service and are still infecting. This is an estimate we made at the beginning of the epidemic in China and other Asian countries,” he explained.
Since April 8, the SSA announced that more people in the country are infected than can be confirmed by PCR laboratory tests. Applying a multiplication factor of 8.4 times, it estimated the existence of 26,519 cases, even though only 3,181 had been established with tests.
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