On the eve of this weekend’s annual San Francisco Pride Celebration and Parade, one of the largest LGBT gatherings in the nation, California public health officials on Friday issued a health advisory about a meningococcal disease outbreak in Southern California, primarily among adult gay and bisexual men.

Meningococcal disease is caused by the bacteria Neisseria meningitidis and can cause meningitis and bloodstream infections. Although rare, the disease is serious and potentially fatal.

Since May, nine men living in Los Angeles and Orange counties — most of whom were gay or bisexual — have contracted the disease, said officials. One patient has died. No cases have surfaced in the Bay Area, according to the state.

“We are concerned that gay and bisexual men in Southern California may be at increased risk for meningococcal disease,” Dr. Karen Smith, the state’s public health officer, said in a statement.

“We encourage men who partner with other men to be aware of the risk of meningococcal disease and consider getting vaccinated.”

Meningococcal bacteria are transmitted through close personal contact and can be spread from person to person by small droplets of respiratory secretions from the nose and throat.

Public health officials said gay and bisexual men may be at increased risk of meningococcal disease if they have close or intimate contact with multiple partners, regularly visit crowded venues such as bars and parties, or smoke cigarettes, marijuana or illegal drugs.

Symptoms of the disease may include fever, vomiting, severe headache, stiff neck, confusion, rash and generalized muscle pains. The time from exposure to the start of symptoms is typically a few days. Anyone who experiences these symptoms should seek medical care immediately, public health officials said.

Six of the nine Southern California cases are known to be caused by a particular strain (serogroup C) of meningococcal bacteria and one other case is awaiting serogroup confirmation, according to the state.

Several outbreaks and clusters of serogroup C meningococcal disease among gay and bisexual men also have been reported in New York City and Chicago since 2014 and recently in Europe, officials said.

As a result, the U.S. Advisory Committee on Immunization Practices this week recommended that all HIV-infected persons ages 2 months and older be routinely vaccinated with the meningococcal vaccine that protects against serogroups A, C, W and Y disease.

State public health officials urge that all HIV-infected adults receive two doses of the vaccine. Gay and bisexual men who are at increased risk for meningococcal disease and are not HIV-infected should receive one dose of the vaccine, they said.

Anyone who has not been tested for HIV within the past year should be offered an HIV test along with vaccination. Adults may locate meningococcal vaccines in their area by using the Centers for Disease Control and Prevention’s Adult Vaccine Finder.