Was Covid-19 present in US in December 2019? It may have infected Americans earlier than thought, says study

CDC scientists found antibodies to coronavirus in 106 samples taken from blood donated by 7,389 people in the US in December 2019 and January 2020


                            Was Covid-19 present in US in December 2019? It may have infected Americans earlier than thought, says study
(Getty Images)

The novel coronavirus may have been infecting Americans as early as December 2019, before public health authorities found the first case in the US in January 2020 and before it was even officially identified in China. This is according to an analysis by the US Centers for Disease Control and Prevention (CDC) and the American Red Cross, among other institutes, which suggests that Covid-19 infections may have been present in the US earlier than previously recognized. 

Covid-19 was first identified in Wuhan, China, with notification to the World Health Organization (WHO) on December 31, 2019, about a cluster of pneumonia cases of unknown etiology and release of the genomic sequence in January. “In the US, the first Covid-19 infection was reported on January 19, 2020, in a returned traveler from China, two days after domestic testing was initiated. While the first confirmed case had a symptom onset date of January 19, 2020, two others within the first 12 US cases identified had illness onset dates of January 14, 2020. Some reports have suggested the introduction of SARS-CoV-2 (the virus that causes Covid-19) into the US may have occurred earlier than initially recognized,” explain investigators. 

To determine if Covid-19 antibodies were present before the first identified case in the US in January, researchers looked at 7,389 routine blood donations collected by the American Red Cross from December 13, 2019, to January 17, 2020, from donors resident in nine states -- California, Connecticut, Iowa, Massachusetts, Michigan, Oregon, Rhode Island, Washington, and Wisconsin. Antibody tests check a person’s blood by looking for antibodies, which may tell if he or she had a past infection with SARS-CoV-2. 

Screening the blood samples, the team found evidence of antibodies to Covid-19 in 106 samples, which indicates those people may have been infected with the coronavirus. These findings suggest that SARS-CoV-2 “may have been introduced into the US before January 19, 2020,” say authors. They, however, emphasize that widespread community transmission was not likely until late February.

This suggests that the virus may have been spreading around the world well before health officials and scientists became aware, upending initial thinking about how early and quickly it emerged.

The routine blood donations were collected by the American Red Cross from December 13, 2019, to January 17, 2020, from residents in nine states (Getty Images)

“These findings indicate that SARS-CoV-2 reactive antibodies were detected in 106 specimens, a small percentage of blood donations from California, Oregon, and Washington as early as December 13-16, 2019. The presence of these serum antibodies indicate that isolated SARS-CoV-2 infections may have occurred in the western portion of the US earlier than previously recognized or that a small portion of the population may have pre-existing antibodies that bind SARS-CoV-2,” write researchers in the journal Clinical Infectious Diseases. They add, “Similarly, antibodies to SARS-CoV-2 were identified among donations occurring in early January in Connecticut, Iowa, Massachusetts, Michigan, Rhode Island, and Wisconsin prior to known introduction of SARS-CoV-2 into those states.”

While positive antibody tests suggest a prior infection with Covid-19, they cannot prove that a person was infected. According to experts, there is a chance that antibodies against other coronaviruses may “cross-react” to give a positive result. Of the 106 “confirmed-reactive specimens,” 90 were available for further testing to account for such cross-reactivity. The investigators found antibodies specific to SARS-CoV-2 in 84 of the samples. Overall, these findings “make it very unlikely that all reactive specimens (positive results) represent false positives,” the findings state. In other words, the team implies that at least some of these positives from December 2019 and early January 2020 were likely due to prior coronavirus infections. They, however, could not confirm whether these infections were community- or travel-associated.

According to scientists, the report also highlights the value of blood donations as a source for conducting SARS-CoV-2 surveillance studies. Data from US blood donation screening have been previously used for population-based incidence and prevalence monitoring during infectious disease outbreaks, most recently the Zika virus epidemic. 

“CDC is continuing to work with federal and non-governmental partners to conduct ongoing surveillance using blood donations and clinical laboratory samples for SARS-CoV-2 infection in multiple sites across the US. Understanding the dynamics of SARS-CoV-2 pandemic from early introduction throughout further progression will advance understanding of the epidemiology of this novel virus and inform the allocation of resources and public health prevention interventions to mitigate morbidity and mortality associated with Covid-19,” the authors conclude. 

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