A 30-year-old man from Chula Vista died on December 10. A 30-year-old man from Los Angeles died on December 16.
West Hollywood resident Brett Shaad, 33, died last week from bacterial meningitis.
The AIDS Healthcare Foundation wants to know whether all three cases of meningitis may be linked to the same bacterial strain.
The foundation's president, Michael Weinstein, says his organization has provided more than 1,000 free meningitis vaccines, and he has challenged LA County to do more.
The Associated Press contributed to this report.