At the party, there were 42 people present. 16 got sick. In many cases husbands got sick first, then wives. All of these are in a close social network (they either work together, or are married to an employee) - so keeping tabs on each other is very likely. Many of them were socially distancing before hand (I can attest to 4 of them, directly) - so external infections are unlikely, but possible.
Due to the timing, the general consensus is that the husbands contacted the disease from one male (close hugging or extended talking) and then gave it to their wives that night.