In San Diego, 14 people have now died as a result of a hepatitis A virus (HAV) outbreak, which experts now believe to be the deadliest outbreak of the liver virus in the United States in almost 20 years, The Guardian reports.

The ongoing health crisis has largely affected the city’s homeless community — so far, 264 people have been hospitalized, roughly 70 percent of them unsheltered, in an outbreak that began last November. San Diego health officials report that nine of the 14 deaths have occurred since mid-July, a troubling acceleration of the death toll.

According to a county spokesperson, epidemiologists have yet to determine the cause of the outbreak. Since hepatitis A can be transmitted through contaminated food, some experts are wondering whether the outbreak might have originated in food that various groups distribute to the city’s homeless residents. The virus can also be transmitted through sharing drugs or beverages, sex, and close personal contact with an infected person. Hepatitis A also has a long incubation period — up to 28 days — which means that people often spread the virus before they’re aware they have it.

Local housing advocates note that San Diego’s homeless community has had to contend with a major lack of 24-hour public restrooms across the city, even though handwashing is one of the best defenses against infection. For this reason, hepatologists are recommending that anyone who is homeless get vaccinated against the virus as soon as possible.

Meanwhile, the speed of San Diego’s response to the crisis has come under scrutiny. While city outreach officials are now officially letting people know where to get free vaccinations and educating them on how to avoid the spread of hepatitis A, many say it’s too little too late. Although the county is now in the process of securing a permit from the city to set up 24-hour handwashing stations, local homeless advocates argue that the stations should have been set up months ago, when the city first detected the outbreak.

Those individuals whose health is already compromised as a result of alcoholism, drug use, exposure or other illnesses also face a much higher risk of death from hepatitis A. Without more urgent action on the part of the city to control the outbreak, many fear the death toll will continue to rise.