Following up on our recent coverage of an atypical Hepatitis A outbreak in Michigan, we wanted to bring attention to another unusual Hepatitis A outbreak ongoing in San Diego, California. As of September 12, this outbreak, which began early this year, has resulted in 421 cases, 16 deaths, and 292 hospitalizations. The San Diego outbreak is particularly noteworthy because traditional methods of containment--vaccination and educational campaigns--have so far not worked to stop the spread, which has prompted public health officials to pursue new strategies.

Hepatitis A is typically spread by eating or drinking food or water contaminated with the virus, and it can often be traced back to a common food source, such as a 2016 outbreak of Hepatitis A in Hawaii linked to raw scallops from the Philippines and a 2016 multistate Hepatitis A outbreak linked to frozen strawberries from Egypt. However, Hepatitis A can also be spread through direct person-to-person contact when an individual does not wash their hands properly after using the restroom and proceeds to touch objects or food or through sexual contact. Officials believe that San Diego’s outbreak is being spread via person-to-person transmission, and through “contact with a fecally contaminated environment,” as no common sources of food or drink have been identified.

According to San Diego’s Health and Human Services Agency, the majority of individuals infected during this outbreak are homeless and/or illicit drug users-- similar to the Michigan outbreak covered previously. Homeless individuals are at particularly high risk for infectious diseases like Hepatitis A because of inadequate sanitation, poor personal hygiene, and risky behaviors such as unprotected sex and drug use, including needle sharing. For example, one seroprevalence study of homeless adults in San Francisco found that 52% were anti-HAV positive, which “was 58% higher than the expected prevalence based on age-specific prevalence rates from the general population.” Hepatitis A outbreaks have occurred previously in homeless populations, including in Bristol, Australia in 2000, in Rotterdam, the Netherlands in 2004, and in Hennepin County, Minnesota in 1999/2000.

The city of San Diego began to combat this outbreak earlier this summer through the promotion of good hand washing practices and increased street cleanings, along with the implementation of vaccination efforts. Additionally, the San Diego Public Health Officer declared the outbreak a health emergency in early September, increasing availability of funding for sanitation measures including portable hand washing stations and power-washing of contaminated surfaces. So far, 40 hand-washing stations have been installed, with plans to add more next week, and street washing were set to begin this week.

Stopping this Hepatitis A outbreak will be difficult, as it has been propagated by numerous highly mobile—and traditionally hard-to-reach—sources (unlike outbreaks that can be traced to one specific food or beverage source) who also lack access to the basic hygienic measures needed to prevent transmission. Additionally, the implementation of hand washing stations does not guarantee their use, and the city will have to rely upon proactive education and outreach campaigns to encourage individuals to use them.

Go here to listen to our colleague, Dr. Amesh Adalja, talk about the San Diego Hepatitis A outbreak.


Outbreak Observatory aims to collect information on challenges and solutions associated with outbreak response and share it broadly in near-real time to allow others to learn from these experiences in order to improve global outbreak response capabilities.