A deadly cluster of bacterial meningitis has erupted among HIV positive gay men in New York City.

It’s left one person dead in the last month and another in a critical condition – according to the Associated Press.

The city’s health department on Thursday issued an alert for “gay men and men who have sex with men.”

The outbreak includes a dozen cases in the last two years, but it seems to have accelerated with four cases in the last four weeks.

Of the 12 total cases, four died.

All four of the men – between the ages of 31 and 42 – who contracted the disease are HIV positive, which the department says puts them at a much greater risk than the general population.

Investigators are trying to find out how the outbreak has managed to spread.

People the men were in close contact with have been treated with antibiotics.

Bacterial meningitis can cause swelling of the membranes covering the brain and spinal cord.

The disease is rare, but people with HIV-weakened immune systems are more susceptible to infection.