Public health officials in Los Angeles County have declared an outbreak of hepatitis A, a highly contagious liver infection driven by a virus that can, in rare cases, cause severe illness.
The condition, which is typically identified in fewer than 50 people in L.A. County each year, infected at least 138 people in 2024 and cases have remained unusually high so far in 2025. Officials say that levels of the virus in local wastewater suggest these figures are an undercount.
Here’s what to know.
How is hepatitis A transmitted?
The hepatitis A virus is spread through the so-called oral-fecal route, which means it is ingested through food or drinks that have been contaminated by microscopic bits of stool from an infected person. It can also spread through close contact with someone who is carrying the virus, even if they don’t show any symptoms.
Unhoused people are often at greater risk of contracting hepatitis A because they have limited access to proper toilets and hand-washing facilities. The virus is also more common among travelers to places with poor sanitation, men who have sex with men and people who use drugs.
But officials say many of the recent cases have occurred in people without those risk factors. They do not yet know why, but Dr. Timothy Brewer, an infectious disease physician and epidemiologist at U.C.L.A., said it had led him to worry about two things: food contamination, and community circulation.
“If you’re practicing good hygiene in a community that has access to potable water, you really should not be seeing a lot of this,” he said. “Something is going on — but exactly what that something is, we don’t yet know.”
What are the symptoms of a hepatitis A infection?
The first signs of the infection can look a lot like a classic stomach bug: fever, fatigue, nausea and a loss of appetite, followed by vomiting and diarrhea. Over time, people who become infected can also experience yellowed skin and eyes, dark urine and pale stools.
One of the challenges to halting a hepatitis A outbreak is that contact tracing can be nearly impossible. The infection can incubate for up to seven weeks before symptoms appear, and a person carrying the virus can spread it for up to two weeks before they feel ill.
In addition, a significant proportion of people who become infected don’t experience major symptoms, said Dr. Edward Jones-Lopez, an infectious disease specialist with Keck Medicine of the University of Southern California, so they do not visit their doctor, who in turn does not run a blood test and report the case.
Severe symptoms are most often seen in older adults, people with chronic liver conditions, and those with weakened immune systems or H.I.V. On rare occasions, a hepatitis A infection can be fatal. In this outbreak, at least seven people have died. That may seem like an unusually high fatality rate, but officials believe far more people have been infected than the official numbers show. Most have probably been asymptomatic, or shown symptoms mild enough to have been misidentified.
How is hepatitis A treated?
There is no specific antiviral medication for hepatitis A. The infection usually resolves on its own within a few weeks, and most people do not face lasting liver damage. But for some, hospitalization can be necessary.
In rare cases, the infection can devolve into an acute liver failure called fulminant hepatitis, which may require a transplant, said Dr. Jones-Lopez. “It can progress very, very quickly — that’s a very serious disease.”
If you think you might be infected, be sure to visit your doctor, drink lots of fluids, and get adequate rest.
How can I avoid it?
The best way to prevent a hepatitis A infection is through vaccination. The regimen — two doses of vaccine, at least six months apart — provides protection for life. It has been routinely given to children for the last two decades, but many adults 25 and older have not gotten the shots unless they were in a high-risk group.
The fact that the outbreak is occurring outside of traditional populations “underscores the need to reassess how — and where — we target prevention efforts,” said Dr. Anne Rimoin, an epidemiology professor at U.C.L.A., since “an infection anywhere is potentially an infection everywhere.”
If you are unvaccinated but know you have been exposed to a person carrying the virus, a prompt vaccination can prevent your becoming infected. Experts say that some people with weakened immune systems who are exposed could also benefit from receiving immune globulin as well. And good hygiene is a wise protective measure for everyone; wash your hands with soap and water, especially after using the bathroom, and before preparing food.