This not-yet-peer-reviewed study, looking for the coronavirus in wastewater samples, is generating a lot of double-takes in surprise, with the surprising suggestion that SARS-CoV-2 virus might have been circulating in Barcelona, Spain as early as March 2019:

This possibility prompted us to analyze some archival WWTP samples from January 2018 to December 2019 (Figure 2). All samples came out to be negative for the presence of SARS-CoV-2 genomes with the exception of March 12, 2019, in which both IP2 and IP4 target assays were positive. This striking finding indicates circulation of the virus in Barcelona long before the report of any COVID-19 case worldwide. Barcelona is a business and commerce hub, as well as a popular venue for massive events, gathering visitors from many parts of the world. It is nevertheless likely that similar situations may have occurred in several other parts of the world, with circulation of unnoticed COVID-19 cases in the community.

(Yes, wastewater treatment plants keep frozen samples of the water going back quite some time. This pandemic teaches us new and often unsavory things every day.)

But some virologists aren’t quite convinced. The study declares, “Both IP2 and IP4 target assays were positive.” IP2 and IP4 refer to particular sequences within the virus gene, called RdRp targets. RdRp is short for “RNA-dependent RNA polymerase,” which is an enzyme that is necessary for the virus to reproduce. In the virus that causes COVID-19, the Institut Pasteur in Paris identified three separate sequences in IP2 and three sequences in IP4.

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The samples in Barcelona might be evidence of SARS-CoV-2, or it may be evidence of a largely-but-not-entirely genetically similar but distinct virus floating around the city in March 2019.

Even a small percentage of difference in a genetic code can turn out to be significant. Chimpanzees and bonobos are about 98.7 percent genetically similar to human beings. Another virus found in horseshoe bats in China is 97.2 percent similar to SARS-CoV-2 — but scientists don’t think it is likely to infect human cells, which for humanity is a pretty key difference!

As for the notion of whether the virus was floating around residents Barcelona in January, well before the first announced case February 25, that seems pretty plausible, particularly in light of the confirmed report that a man in France caught the virus in December. It is believed he caught it from his wife, who worked at a supermarket near Charles de Gaulle airport and could have come into contact with people who had recently arrived from China. Travelers from China in December and early January could well have started the spread of SARS-CoV-2 well before doctors in Spain realized that it was a novel coronavirus.