Before the national infectious-disease rollout, health officials spent months urging Americans to limit social gatherings and keep celebrations to within members of their household. Now, a study assessing the association between informal social gatherings and SARS-CoV-2 transmission suggests that birthday parties, especially those involving children taking place in counties with the prevalence of virus, resulted in increased rates of diagnosed COVID-19.
The study, published in JAMA, analyzed the potential increased risk of COVID-19 around small social gatherings by studying changes in COVID-19 rates after birthday parties. The study, which specifically looked at the changes in household COVID-19 infection rates after the presence of a birthday in the household, included data from January through November 2020.
The researchers also separated children’s birthdays and adult birthdays into two different categories. Overall, data from over 6.5 million individuals from 2.9 million households were analyzed. The researchers found that a presence of a birthday within a household was associated with greater rates of COVID-19 diagnosis, with the risk highest in counties with a high prevalence of the disease.
“The estimated increase in COVID-19 infections in households with birthdays was larger in magnitude in households that had a recent child’s (vs adult’s) birthday, suggesting an increased likelihood of gathering around children’s birthdays, a large number of participants, relaxed masking and social distancing behavior, or a combination of these,” the researchers wrote. “Households may also be more likely to have a social gathering for a child’s birthday than for an adult’s birthday.”
The researchers noted that the increase in infections was not greater for milestone birthdays, nor was there a decrease in infections in households located in counties with an active shelter-in-place order.
The authors noted that the study was observational in nature and that it relied on administrative health care data for COVID-19 diagnoses rather than lab-confirmed data. The study was also “unlikely to capture asymptomatic cases” that did not require medical attention, as the diagnoses included in the data appeared in medical claims data.