As they attempt to curb an outbreak of invasive meningococcal disease in Los Angeles County, health experts say they don't know why it's disproportionately affecting gay and bisexual men.
Twelve L.A. County residents have contracted meningitis in the past two months; seven of them have been gay or bisexual men.
"In L.A. County there are an estimated 300,000 self-identified gay or bisexual men, in a population of more than 10 million," said Dr. Jeffrey Gunzenhauser, interim health officer for the County Department of Public Health. "Seven cases occurring among this group, during a two-month period, is much higher than expected."
Meningitis is spread through close contact with an infected person. People can contract it through kissing, coughing or sneezing, or sharing cigarettes or drugs. It also spreads among people in group settings – like dorms, jails or shelters.
Gunzenhauser offered several possible explanations as to why gay and bisexual men seem more susceptible to contracting meningitis.
"There's one theory that it's all about the organism," he said, adding that it's possible that some strains of the organism that cause meningitis are more infectious than others.
When the organism gets into a community, "perhaps in a community where there's some type of autoimmune issue, or even in a community where there's a lot of contact, where people get together socially regularly, that organism would be more likely to spread," said Gunzenhauser.
"There's another theory that it's about the person," he said.
"There's quite a few people that are carrying the organism, but it really doesn't pose any risk to them," said Gunzenhauser. "But there's the rare person – we don't really know what the percentage is – but if they get this infection, they are susceptible to this invasive disease and very serious outcomes."
Symptoms of meningitis usually occur within five days. They include high fever, stiff neck, skin rash, severe headache, low blood pressure, sensitivity to bright lights and generalized muscle pains. The infection can cause brain damage, hearing loss and death. It progresses quickly, so immediate diagnosis and treatment is imperative, health experts say.
Gunzenhauser said the county has failed to find commonality among those who have contracted the disease.
"We really interview each case, ask them where they’ve been – the incubation period for this disease is 10 days – so we normally go back about 10 or 14 days, ask them where they’ve been, who they’ve been with, then we compare all of the cases to see if there’s any locations or common connections," he said.
"To date we have not been able to find a single connection between any of the cases," he said.
Dr. Robert Bolan, medical director of the L.A. LGBT Center, speculates that social factors could make gay men more vulnerable to meningitis.
"Anecdotally, some people think that gay men are more demonstrative towards one another than the general population - there's more kissing, more deep kissing," Bolan said. "I don't know whether that's true or not."
He pointed to another commonly held belief, that "gay and bisexual men are said to have more sexual partners than average heterosexual individuals. I suspect that is in fact true."
The surge in meningitis cases is not without precedent: Since 2014, outbreaks of a particular strain of meningitis have been reported among gay and bisexual men in L.A. County, New York City and Chicago, according to the California Department of Public Health. Similar outbreaks have also been reported recently in Europe.
In the 2014 L.A. County outbreak, there were 11 cases, and six were among gay and bisexual men, according to County Public Health.
Following the 2014 outbreak, the L.A. LGBT Center's Bolan urged the Centers for Disease Control and Prevention to determine why gay and bisexual men seem to be at greater risk of exposure to, and transmission of, meningitis than the general population.
As a result, he said, the CDC and the New York City Department of Public Health recently launched a study of 800 people at two clinics in New York City.
"This study should help answer some of the important questions and point the way to broader screening and prevention policies," Bolan said.
Whatever the reasons for gay and bisexual men's greater susceptibility to meningitis, health officials are urging them to get vaccinated. This includes those who have multiple partners, who seek partners using digital apps, or who use drugs and/or share cigarettes or marijuana.
All HIV-infected people routinely receive the meningococcal vaccine, according to the U.S. Advisory Committee on Immunization Practices.