Men who have sex with men are at risk for a potentially deadly strain of meningitis, warns the New York City Department of Health, which is urging gay and bisexual men to get vaccinated against the virus.

Health-department officials first made an announcement about the outbreak in September:

The Health Department is currently investigating a cluster of invasive meningococcal disease, commonly known as meningitis, among gay men and men who have sex with men. Invasive meningococcal disease is a severe bacterial infection that has a high fatality rate. Within the past four weeks, there have been four cases; one died and one person is in critical care. The cases are spread across several boroughs and among men ages 31 to 42 years old.

At that time, the warning was primarily for HIV-positive men, as the four infected men were all HIV-positive. But now they’ve widened their net, saying “all men who are intimate with other men they’ve met on a website or an app or at a bar or a party need to get vaccinated now.”

Some 17 cases have been reported locally since 2012, and seven deaths have attributed to the disease since 2010.

Symptoms of meningitis—which include high fever, headache, stiff neck and rash—can appear as quickly as two days after exposure. “The time from being infected to being horribly sick and possibly dying is very short,” Deputy Health Commissioner Dr. Jay Varma told WCBS 880. “We’ve had several cases who have been actually found dead in their apartment before they’d even gone to see a medical provider. So that is, to us, absolutely terrifying.”

Health Commissioner Dr. Thomas Farley says vaccination is the best defense: “I urge all men who meet these criteria – regardless of whether they’re identify as gay – to get vaccinated now and protect themselves from this disease before it is too late.”

If you live in New York, find the nearest clinic with the Health Department’s Site Locator.