A hepatitis A virus (HAV) outbreak moving through San Diego’s homeless population has killed at least three people and hospitalized more than 60, according to a public health alert released last week by the city, The San Diego Tribune reports.

The county’s Health and Human Services Agency is advising anyone who has close contact with homeless individuals to get vaccinated in order to prevent an infection. Hepatitis A is transmitted orally through shared food, drink or drugs — typically when an infected person fails to wash his or her hands after using the bathroom — but investigators have not identified the source of the outbreak.

In addition to affecting homeless people, seven of the 80 hepatitis A cases confirmed by the county since it started tracking the epidemic in November 2016 have occurred in local detention facilities. Most of those infected individuals, health authorities noted, were previously homeless, though the city is reporting a few secondary cases of hep A transmission (instances in which an inmate was infected by a newly arrived arrestee).

Local health officials also say tracking the hep A outbreak has been difficult, as most infected patients interviewed at the hospital do not appear to have fixed addresses. What’s more, San Diego health authorities say that by the time they get a report of a new HAV infection, patients have often already been discharged from care.

Over the last few weeks, San Diego county has conducted several mass hepatitis A vaccination clinics with the help of organizations across the city that serve the homeless. But since new infections continue to pop up, the city has decided to put together small public health teams to dispatch into the community within the next two weeks.

Although there is currently no treatment for a hepatitis A infection, those exposed to the virus can be treated with immunoglobulin antibodies within two weeks to help their body fight off the infection. San Diego authorities also noted that anyone who is age 23 or older was born before the hepatitis A vaccine existed and may not be protected from the virus.