Study: 56% of adults infected with Omicron did not know they were contagious

Observational study of 210 adults in California with detectable antibodies to SARS-CoV-2 during an Omicron variant wave shows 56% were unaware they had been infected, fueling concerns about transmission asymptomatic, according to a report published today in Open JAMA Network.

Researchers at Cedars-Sinai Medical Center conducted the study on adult employees and patients at Los Angeles County Hospital who had at least two SARS-CoV-2 antibody tests at 1 month or more d ‘interval. The first test took place after the Delta variant surge on September 15, 2021 and the second was carried out in the middle of the Omicron wave from December 15, 2021 to May 4, 2022. Participants also completed surveys on vaccinations, viral exposures and symptoms at baseline. and throughout the study.

Investigators called the study the first to assess sensitization to Omicron infection, which is critical for timely self-isolation, in a diverse urban area in the United States.

10% had symptoms attributed to a cold or another illness

Of the 210 participants, the median age was 51, 65% were female, 44% knew they had a recent Omicron infection, and 56% said they did not know they were infected. Of the 118 participants who were unaware of their infection, 12 (10%) reported having symptoms but attributed them to a cold or other non-COVID infection.

A multivariate analysis showed that overall awareness was low but center staff were more likely than patients to know they were infected (odds ratio adjusted [aOR]2.46).

“This finding may be explained not only by differences in general health awareness and literacy between employees and non-employees, but also by the mandatory daily screening protocols for employees that are supported by health policies. ‘COVID-19 sickness benefits, which were expanded at the institution during the Omicron Variant Surge,’ the study authors wrote.

Of the 92 participants who were aware of their infection, 67 (73%) had a positive polymerase chain reaction (PCR) result recorded in their electronic health record, self-reported the result, or both.

An unadjusted analysis showed that participants who knew they were infected were more likely to be younger than those who didn’t (47 versus 53). Men were also more likely than women to know they were infected (OR, 1.87).

“If these results prove generalizable, they could be associated with the tendency of some individuals to develop a greater symptomatic response or more severe forms of infection with the Omicron variant,” write the authors. “The extent to which self-reported awareness of the Omicron variant or symptoms of infection appeared lower in older participants may be associated with poorer recall in survey ratings.”

Of the 92 participants who were aware of their Omicron infection, 62 (67%) indicated awareness when surveyed, with 56 (90%) reporting symptoms attributable to COVID and 6 (10%) reporting no symptoms .

Prior to detection of SARS-CoV-2 antibodies, 94% of participants had received a COVID-19 vaccine and 93% of previously vaccinated participants had completed a series with at least one mRNA vaccine.

Role of antibody tests

The researchers noted that while general access to COVID-19 testing may have improved over time, Omicron has been linked to milder disease than that caused by previous strains of SARS-CoV-2. The milder nature of the infection may have led infected people to spread the virus unknowingly.

“Lack of awareness of infection with the Omicron variant, either due to the relative absence of symptoms or lack of timely testing, likely played a role in the rapid transmission within communities across the country. Los Angeles County,” they wrote.

They added that antibody tests can complement rapid antigen tests and household and wastewater surveillance programs to understand trends in susceptibility to emerging strains of SARS-CoV-2.

“The greater availability and use of rapid antigen tests may be associated with increased awareness and, in turn, reduced rates of person-to-person transmission of the Omicron variant,” the researchers concluded. “Further studies are needed to more fully understand the factors associated with ignorance of infection status, particularly factors that could be mitigated by available interventions.”

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