Hepatitis A, also spread primarily through feces, infected more than 1,000 people in Southern California in the past two years. The disease also has erupted in New Mexico, Ohio, and Kentucky, primarily among people who are homeless or use drugs.

Public-health officials and politicians are using terms like disaster and public-health crisis to describe the outbreaks, and they are warning that these diseases can easily jump beyond the homeless population.

Read: The next plague is coming. Is America ready?

“Our homeless crisis is increasingly becoming a public-health crisis,” California Governor Gavin Newsom said in his State of the State speech in February, citing outbreaks of hepatitis A in San Diego County, syphilis in Sonoma County, and typhus in Los Angeles County.

“Typhus,” he said. “A medieval disease. In California. In 2019.”

The diseases have flared as the nation’s homeless population has grown in the past two years: About 553,000 people were homeless at the end of 2018, and nearly one-quarter of homeless people live in California.

The diseases spread quickly and widely among people living outside or in shelters, helped along by sidewalks contaminated with human feces, crowded living conditions, weakened immune systems, and limited access to health care.

“The hygiene situation is just horrendous” for people living on the streets, says Glenn Lopez, a physician with St. John’s Well Child & Family Center, who treats homeless patients in Los Angeles County. “It becomes just like a Third World environment, where their human feces contaminate the areas where they are eating and sleeping.”

Those infectious diseases are not limited to homeless populations, Lopez warns: “Even someone who believes they are protected from these infections [is] not.”

At least one Los Angeles city staffer said she contracted typhus in City Hall last fall. And San Diego County officials warned in 2017 that diners at a well-known restaurant were at risk of hepatitis A.

There were 167 cases of typhus from January 1, 2018, through February 1 of this year, up from 125 in 2013 and 13 in 2008, according to the California Public Health Department.

Typhus is a bacterial infection that can cause a high fever, stomach pain, and chills but can be treated with antibiotics. Outbreaks are more common in overcrowded and trash-filled areas that attract rats.

The recent typhus outbreak began last fall, when health officials reported clusters of the flea-borne disease in downtown Los Angeles and Compton. They also have occurred in Pasadena, where the problems are likely due to people feeding stray cats carrying fleas.

Last month, the county announced another outbreak in downtown Los Angeles that infected nine people, six of whom were homeless. After city workers said they saw rodent droppings in City Hall, Los Angeles City Council President Herb Wesson briefly shut down his office to rip up the rugs, and he also called for an investigation and more cleaning.