The death toll from California's hepatitis A outbreak has reached 19, one week after the state's governor issued a health state of emergency.
More than 500 people in California have contracted the viral disease since November, many of whom are homeless.
Hepatitis A, which attacks the liver, is usually spread through faecal matter, transmitted through sex or by touching contaminated food or objects.
It is the second-largest US outbreak of hepatitis A in the past 20 years.
Nearly 500 of the diagnoses have been reported in San Diego, where officials have taken steps to combat the outbreak by disinfecting city streets with bleach and setting up hand-washing stations.
A local city councilman has called for state environment researchers to test San Diego's drinking water for faecal contamination, which causes the liver disease.
The outbreak has taken a severe toll on the state's large homeless populations, which are most at risk as they do not have access to basic hygiene and sanitation, experts say.
The virus is transmitted from faeces to mouth, which means it is most likely to spread in unsanitary conditions.
More than 5,000 people are sleeping unsheltered in San Diego - a 10% increase from the year before - according to a recent study by the Regional Task Force on the Homeless.
Cases have also been reported in Santa Cruz and Los Angeles counties as well as in San Francisco in northern California, where officials say they have vaccinated thousands of homeless people.
Typically only one out of every 100 patients die from Hepatitis A, according to officials, but the disease has killed at a higher rate in California due to the vulnerable populations it has affected.
Symptoms include fever, fatigue, abdominal pain, nausea and vomiting. Jaundice, or yellowing of the skin and eyes, is also a possible symptom.
On 13 October, Governor Jerry Brown issued a state of emergency in order to ensure that vaccines reach medical clinics who are working with the homeless.
Health officials have advised that it may take months or years before the outbreak tapers off.