... A new, casually transmittable infection — a unique strain of bacterial meningitis — has cast a pall over the gay night life and dating scene, with men wondering whether this is AIDS, circa 1981, all over again. Seven men have died in New York City, about a third of diagnosed cases, since 2010. And in the last few months, the contagion seemed to be accelerating. It has targeted gay and bisexual men, and nobody knows exactly why. The city’s best hope to curb the outbreak is to vaccinate as many at-risk men as possible, focusing on those most in...