Notes from the Field: Genomic and Wastewater Surveillance Data to Guide a Hepatitis A Outbreak Response — Los Angeles County, March 2024–June 2024

In April 2024, the Los Angeles County (LAC) Department of Public Health (DPH) identified three cases of hepatitis A virus (HAV) infection among persons experiencing homelessness (PEH) through routine surveillance,* compared with one case identified among PEH during the preceding 6 months.HAV is a highly infectious fecal-oral transmitted virus that infects the liver.Most infected persons recover without sequelae, but it can rarely cause liver failure and death.Inadequate access to hygiene and sanitation services is a risk factor for HAV infection.Traditional case-based surveillance for HAV is challenging because persons with HAV are infectious for ≤2 weeks before symptom onset, and approximately 30% of infected persons do not experience symptoms.Further, health care providers might not suspect HAV infection because the early symptoms of HAV infection can be nonspecific (e.g., fever, nausea, abdominal pain, and diarrhea), and 30% of symptomatic cases will not develop jaundice to indicate hepatitis.Genomic and wastewater surveillance data helped confirm an outbreak and guide response activities by illustrating the magnitude of HAV transmission potentially undetected by case-based surveillance.