The Chicago Department of Public Health says six human cases of leptospirosis have been reported so far in 2025, exceeding the city’s expected numbers for the rare disease, according to an alert issued Tuesday.
Four of the most recent cases involve exposure in the city’s Logan Square and West Town neighborhoods, said Jacob Martin, a spokesperson for the city’s department of public health. All four cases involved direct contact with animal urine or droppings, particularly from rats, or indirect exposure to rodents through gardening or yard work, he said.
The recent spike in leptospirosis cases started in mid-July. The other cases from this year did not all involve exposure in Chicago, Martin said.
Leptospirosis is caused by the Leptospira bacterium and spreads when urine from infected animals contaminates water, soil or food and enters the body through cuts or mucous membranes, the alert states. Outbreaks are more likely after heavy rain and flooding.
Communities around Chicago have dealt with multiple incidents of flooding this summer.
The U.S. Centers for Disease Control and Prevention describes leptospirosis as an infection found worldwide, though more often in tropical climates.
Chicago typically sees about two cases per year. And some years there are as few as one case. From 2015 to 2025, there were 28 reported cases in the city, according to the alert.
“Most people don’t know what leptospirosis is,” said Dr. Emily Landon, the executive medical director of infection prevention and control for the University of Chicago.
Landon noted that while the disease is associated with warmer climates, “climate change is happening and diseases are changing in terms of where they appear.”
Alerts like CDPH’s help doctors consider testing sooner for certain diseases, she said. The illness can resolve on its own, though for some patients it can cause more serious diseases that affects the kidneys and liver, she said.
Landon said outbreaks have been tied to freshwater exposure and cited a past cluster linked to a triathlon swim in Lake Springfield in Illinois.
“You don’t need to freak out if you see a rat,” Landon said, but residents should avoid contact with rodent waste and take precautions when working in soil or around standing water.
According to the city health department alert, symptoms can begin five days to two weeks after exposure and may start with fever, chills, muscle aches, nausea, vomiting, diarrhea, abdominal pain and cough.
Martin said residents can reduce risk by avoiding contact with floodwater and not eating food contaminated by floodwater.
Residents are also encouraged to report rodent sightings to 311, secure lids on trash bins and seal entry points where possible to keep rats out of yards.
When working near animal urine or feces, people should wear plastic gloves, disinfect thoroughly and wash their hands afterward.
When gardening, doing yard work or standing in water, cover wounds with waterproof bandages and wear waterproof gloves and closed‑toe shoes or boots.
Pet owners should also talk to their veterinarians about leptospirosis vaccination for dogs, he said.