Variables and data sources/measurement

Objective outcome: The main outcome was the participants' SARS-CoV-2 antibody laboratory test result. The virus can cause an immune response in both symptomatic and asymptomatic individuals [^14,15]. The antibody test kits we used were SARS-CoV-2 IgM/IgG rapid assay kit (Colloidal Gold method). These kits can detect IgM and IgG antibodies against SARS-CoV-2 in the blood and provide accurate and rapid results at the testing site. If the antibody test result was negative for both IgM and IgG antibodies, the antibody test result was coded as negative. Otherwise, if the test kit results for any of the two types of antibodies were positive, the outcome was coded positive.

Self-reported outcome: The second outcome of interest was self-reported SARS-CoV-2 testing history. This was measured by the following questions in the baseline survey.

“Have you ever been tested for SARS-CoV-2 (COVID-19) before? Note: By this, we mean testing for active infections, usually done with a nasal swab or saliva test” (Responses: “Yes,” “No,” “Don't Know”).

[Displayed if one equals Yes] “Have you ever tested positive for a SARS-CoV-2 (COVID-19) infection?" (Responses: “Yes,” “No,” “Don't Know”)

Participants who responded “Yes” to both questions were categorized as ever tested positive for SARS-CoV-2.

We collected data on the following baseline characteristics and potential risk factors for a positive SARS-CoV-2 test result: age (≥22 years vs. <22 years), sex at birth (female vs. male), race (Asian, black, multiracial, other, White), Hispanic or Latinx ethnicity (yes vs. no), year in school (first through fifth), residence (on-campus vs. off-campus), Greek membership (yes vs. no), relationship status (multiple partners, single partner, no partner), and know others who were infected (yes vs. no). Moreover, among those who self-reported a positive SARS-CoV-2 testing history, we collected data about their symptoms, symptomatic (yes vs. no). Age was collected as a continuous variable but was dichotomized for analysis. Undergraduate students are mainly 18–22 years of age. We recoded this continuous variable as categorical with 22 years of age as the cutoff point.

Moreover, we collected alcohol use data using the following two variables: (1) Number of days per week drinking alcohol: This variable was collected continuously and could range from 0 to 7 days a week. In our inferential analyses, we used the median of one as the cutoff point for this variable (>1 day in a week vs. ≤1 day in a week). (2) Number of people hanging out with while drinking: This continuous variable measured the number of people students hung out with while drinking. It was only measured among those who reported drinking alcohol (i.e., drinking more than 0 days a week) and could range from 0 to 1,000. In our inferential analyses, we used the median of five as the cutoff point for this variable (>5 people vs. ≤5 people). All the aforementioned predictors were self-reported in the online baseline survey. ^{Appendix A} includes the survey questions used. Figures in ^{Appendix B} show the distribution for continuous variables.