Respiratory virus risk factors: Close contact for COVID, youth for rhinovirus

The greatest risk factor for COVID-19 was close contact with an infected person (adjusted odds ratio [aOR], 3.89) (although the difference in risk of infection after exposure to an asymptomatic or symptomatic person was not significant), followed by loss of smell or taste (aOR, 3.49). Both associations weakened after the Omicron variant became predominant.

The odds of COVID-19 test positivity were lower after contact with an infected, vaccinated person (aOR, 2.03) than with an infected, unvaccinated person (aOR, 4.04). Sore throat was a risk factor for Omicron (aOR, 2.27) but not Delta infection. COVID-19 vaccine effectiveness (VE) for participants who had received a primary series plus a booster dose was 93% for Delta but was not significant for Omicron.

Participants vaccinated with a primary COVID-19 series and those who also received a booster within the past 6 months and those with a previous positive test at least 90 days earlier or who reported attending or working at a school in the past 14 days were all significantly less likely to test positive. Among symptoms, loss of smell or taste (aOR, 3.5), cough (aOR, 2.5), and fever (aOR, 2.4) were most associated with a positive test.

Risk factors for rhinovirus infection were age younger than 12 years (aOR, 3.92) and a stuffy or runny nose (aOR, 4.6). Black race (aOR, 2.0), Hispanic race (aOR, 2.1), residence in a high-risk census tract (aOR, 1.5) or in a household with five or more people (aOR, 1.4), attending or working at a school (aOR, 2.0), and international travel in the past 14 days (aOR, 2.3) were associated with both COVID-19 and rhinovirus positivity.

Improving targeted interventions

The study authors noted that early US COVID-19 studies identified close contact and workplace and community exposures as important risk factors, and many studies also found that Black, Hispanic, and socioeconomically vulnerable populations were disproportionately infected. But few studies have revisited these risk factors in the context of broad vaccination, increasing infection-conferred immunity, and circulation of new variants.

"Estimated risk factors and symptoms associated with SARS-CoV-2 infection changed over time," they wrote. "There was a shift in reported symptoms between the Delta and Omicron variants as well as reductions in the protection provided by vaccines."

The higher COVID-19 risk in Black and Hispanic people and those of lower socioeconomic status may be explained by the need to work onsite and larger household size, the researchers said.

"We did not have data for other variables that may influence disparities in exposure risk, such as household crowding (people per room), household income, and access to health care, transportation, or personal protective equipment, but acknowledge these could be important variables," they wrote. "Continued efforts to understand the drivers of respiratory virus infections in the postpandemic period remain important to improve targeted interventions."