How many conferences were happening in the US at the same time? Why would one of them be singular, or unusual, in terms of spread, aside from a conference that simply had no infected attendee?
And aside from some conference, we had "business as usual" congregations, meetings, churches, hotels, bars, concerts, you name it, not to mention cruise ships etc.
Atlanta is a major convention city, and no doubt held major conventions in Jan/Feb as well (none since March).