AS cases of meningitis, a rare and potentially fatal disease, popped up in cities nationwide over the past several years, public health officials noticed a trend: many of those infected were gay men. There’s no known medical reason why meningitis, which is transmitted through saliva, would spread more among gay and bisexual men. Yet New York, Chicago and now Southern California have experienced outbreaks disproportionately affecting that population. “It is perplexing,” said Dr. Rachel Civen, a medical epidemiologist at L.A. County’s Department of Public Health. Of the 13 cases of meningitis this year in L.A. County — excluding Long Beach,...