Chicago Health Officials Report Rise in Rare Rat-Linked Illness
Introduction to Leptospirosis
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.
Causes and Spread of Leptospirosis
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.
Recent Spike in Cases
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. 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.
Expert Insights
“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.
Prevention and Precautions
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.
Reducing Risk
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.
Conclusion
The rise in leptospirosis cases in Chicago is a concern for public health officials, and residents are advised to take precautions to reduce their risk of exposure. By understanding the causes and spread of the disease, as well as taking steps to prevent it, residents can help mitigate the risk of leptospirosis. It is essential for residents to be aware of the symptoms and to seek medical attention if they suspect they have been exposed.
FAQs
Q: What is leptospirosis?
A: Leptospirosis is a rare disease caused by the Leptospira bacterium, which spreads through contact with contaminated water, soil, or food.
Q: How can I reduce my risk of exposure?
A: Avoid contact with floodwater, do not eat food contaminated by floodwater, report rodent sightings, secure trash bins, and seal entry points to keep rats out of yards.
Q: What are the symptoms of leptospirosis?
A: 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.
Q: Can leptospirosis be prevented in pets?
A: Yes, pet owners should talk to their veterinarians about leptospirosis vaccination for dogs.
Q: Is leptospirosis a serious disease?
A: While the illness can resolve on its own, it can cause more serious diseases that affect the kidneys and liver in some patients.
