Meningitis is a rare and potentially fatal disease that has popped up in cities nationwide over the past several years and public health officials are noticing a trend: Many of those infected were “gay men”. This has left experts puzzled because there’s no known medical reason why meningitis, which is transmitted through saliva, would spread more among gay and bisexual men.

Excerpt from New York Times:
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.