Coronavirus pandemic: There maybe 5 to 10 undetected cases for every confirmed one, say worried scientists
For every known case of coronavirus, there are most likely another five to 10 people in the community with infections that have not been detected yet.
These findings are from a new study that tries to answer a critical question on how many infected people might go undetected in a country. The findings are particularly worrying for the US as the worst-case scenario projection for the country by the US Centers for Disease Control and Prevention (CDC) shows that 160M to 214M Americans could be infected in the COVID-19 pandemic.
"If we have 3,500 confirmed cases in the US, you might be looking at 35,000 in reality," study author Jeffrey Shaman — an epidemiologist from the Mailman School of Public Health, Columbia University, New York, — told the New York Times.
The US has been severely criticized for messing up its testing, which health experts believe has allowed the virus to go undetected and move freely, leaving many Americans without a diagnosis. Experts have repeatedly said that currently, because the US does not have enough tests, it is not clear how many Americans are infected with COVID-19. To check community transmission, US President Donald Trump recently issued new guidelines, asking Americans to avoid groups of more than 10 people for 15 days.
In the US, the number of reported infections has crossed over 14,200 across 50 states. So far, 205 deaths have been reported from the US. Washington (74 deaths), New York (38), and California (18) have reported the maximum number of deaths so far. Meanwhile, the global death toll has crossed 10,000 and at least 244,400 have fallen sick with the virus.
"The fraction of undocumented but infectious cases is a critical epidemiological characteristic that modulates the pandemic potential of an emergent respiratory virus. These undocumented infections often experience mild, limited or no symptoms and hence go unrecognized, and, depending on their contagiousness and numbers, can expose a far greater portion of the population to the virus than would otherwise occur," the research team from the UK, the US, China and Hong Kong says in their findings.
The findings
The researchers modeled the virus's natural spread in China before the government implemented travel restrictions. The team estimates that 86% of all infections were undocumented before January 23 travel restrictions. According to the study, "The transmission rate of undocumented infections was 55% of documented infections." Meaning, that these undocumented infections were 55% as contagious as documented infections. Undocumented infections were the infection source for 79% of documented cases, says the team. These findings explain the rapid geographic spread of COVID-19 and indicate containment of this virus will be particularly challenging, says the team.
"During January 10-23, only 14% of total infections in China were reported. This estimate reveals a very high rate of undocumented infections: 86%. This finding is independently corroborated by the infection rate among foreign nationals evacuated from Wuhan. These undocumented infections are estimated to have been half as contagious per individual as reported infection," says the study published in Science.
The researchers estimated 13,118 new COVID-19 infections (documented and undocumented combined) during January 10-23 in Wuhan city. They say 86.2% of all infections were from undocumented cases. "Nationwide, the total number of infections during January 10-23 was 16,829 with 86.2% infected by undocumented cases," says the study.
It further says, "Overall, our findings indicate that a large proportion of COVID-19 infections were undocumented prior to the implementation of travel restrictions and other heightened control measures in China on January 23 and that a large proportion of the total force of infection was mediated through these undocumented infections."