Are you allowed to go daven with a minyan when you have the flu or other highly contagious illness? Is it considered potentially damaging someone else's health, or are the chances of someone else getting it from you small enough that that shouldn't be a factor? In addition, can you trust the others members of the minyan falling under "Shluchei Mitzvah Einan Nizokim"?
Preventing the Flu: Good Health Habits Can Help Stop Germs
- Avoid close contact. Avoid close contact with people who are sick. When you are sick, keep your distance from others to protect them from getting sick too.
2. Stay home when you are sick. If possible, stay home from work, school, and errands when you are sick. You will help prevent others from catching your illness.
I have not seen any specific halachic references to this point.
I think Hillel's maxim דעלך סני לחברך לא תעביד (Shabbos 31) is applicable.
Would you like to daven in a minyan with someone who had the flu?
R. Akiva Eiger (Igrot Sofrim 29) was asked whether minyanim should be held during a cholera outbreak or whether public gatherings should be avoided altogether. His response was that they should continue holding minyanim but in an open area, in groups no larger than 15, where the same 15 people always daven together. This is a compromise where one limits the spread of the disease without giving up tefillah b'tzibbur.
Of course, cholera is more severe than flu for most people, but in R' Eiger's case, no one yet had cholera in the group. My answer would be different if the minyan one goes to is populated by college students than if it were populated by octogenarians.