A deadly cluster of bacterial meningitis has erupted among HIV-infected gay men in New York City. It's left one person dead in the last month and another in critical condition.

The city's health department on Thursday alerted local doctors about the outbreak. It 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.

Investigators are trying to find out how the infection spread. People the men were in close contact have been treated with antibiotics.

Bacterial meningitis and an associated blood 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.