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.

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“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.

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New York City, where the majority of the homeless population lives in shelters rather than on the streets, has not experienced the same outbreaks of hepatitis A and typhus, says Kelly Doran, an emergency-medicine physician and assistant professor at New York University. But Doran says different infections occur in shelters, including tuberculosis, a disease that spreads through the air and typically infects the lungs.