'More Than Expected' Cases Of Rat-Borne Disease Reported In Chicago: Department Of Health

CHICAGO — Considering they historically only see around two cases per year, officials from the Chicago Department of Public Health are warning residents that the number of reported leptospirosis cases has already tripled for 2025. The disease is transmitted to humans by exposure to infected animal urine, often through contaminated water or soil.

Of the six cases in Chicago, four were reported between July and August, and all involved direct exposure to animal waste (particularly from rats) or indirect exposure to rodent waste through gardening/yard work.

According to CDPH, the majority of clinical cases of leptospirosis are mild, but approximately 10 percent of cases become severe and life-threatening, including hepatic and renal failure, and in some cases, pulmonary hemorrhage.

In the United States, health officials said approximately 100 to 150 cases of leptospirosis occur annually. Outbreaks are more likely to happen after heavy rain and flooding. Over the last 10 years, 28 cases have been reported in Chicago. The local cases have mostly occurred in men and tend to peak in summer months. CDPH said the recent cases have been largely clustered around the Logan Square and West Town community areas.

Symptoms commonly include fever, chills, body aches (especially in the calves and lower back), nausea, vomiting, diarrhea, abdominal pain, cough, conjunctival suffusion and sometimes, skin rash.

All cases of leptospirosis must be reported to CDPH through I-NEDSS or by calling 312-743-9000, option number 7. See the complete CDPH health alert here.