New York City is dealing with an unusual outbreak of a rare, sometimes fatal disease spread through rat urine, called leptospirosis. At least 15 locals have contracted the bacterial disease in 2021 so far, according to health officials, with most hospitalized and one person dead as a result. It’s not known why cases have been more common this year, though warmer weather conditions fueled by climate change may be a factor.
Leptospirosis, also called Weil’s disease, is caused by thin, corkscrew-shaped Leptospira bacteria. It’s a zoonotic disease, meaning that infections are transmitted to humans through animals, in this case their infected urine. This can happen through direct contact with urine or when the urine contaminates the environment, such as our food and water. The bacteria can still be contagious for weeks to months once introduced to the environment under the right conditions.
Not everyone becomes sick after getting the infection, and its vague symptoms can make diagnosis difficult at first. These symptoms include high fever, chills, muscle aches, and jaundice (yellowed skin and eyes). Sometimes, people may recover from this first bout only to experience a worse and more life-threatening second phase of illness, one that can severely damage the liver, kidneys, and brain. This second stage is more common when the infection isn’t promptly treated with antibiotics.
Leptospirosis is found all over the world, according to the Centers for Disease Control and Prevention, and it may cause more than 1 million infections and around 59,000 deaths annually. But in the U.S., it’s rarely reported, with around 100 to 200 cases documented yearly, with most coming from Puerto Rico. In New York City, according to health department data, 57 cases of leptospirosis were documented over a 15-year span from 2006 to 2020, or fewer than 4 cases a year on average. That makes 2021 a big outlier for the city.
In late September, the NYC Department of Health issued a public advisory after they had documented 14 cases of leptospirosis; since then, a 15th case has been found. The cases are scattered across all boroughs, save Staten Island, and, of the first 14, only one is thought to have been caught during travel elsewhere. In its advisory, health officials said that 13 people had been hospitalized with acute kidney and liver failure, with two developing serious lung problems as well. One person died from their infection, though others hospitalized have since been discharged.
Leptospirosis can be transmitted through a wide range of animals, including our pets. But historically, cases in NYC are associated with rat infestations. All of the local cases were found in people exposed to environments with severe rat problems, including three people without housing. Health officials say they’ve conducted inspections of suspected hot spots and have tried to remedy the rat infestations when needed. Rat sightings in the city this year have gone up in 2021 compared to last year, though this may represent greater social activity on our part rather than any rat resurgence.
It’s known that the risk of leptospirosis in an area can climb after flooding from hurricanes and other extreme weather. That’s because infected urine trapped in the soil or elsewhere can easily contaminate floodwater, which can be hard for people to avoid touching. In 2017, for instance, the U.S. reported a high of 195 cases, with most of the increase coming from Puerto Rico and the U.S. Virgin Islands after they experienced Hurricanes Irma and Maria back to back that September.
Though NYC did experience historic flooding caused by the tail end of Hurricane Ida this year, none of the cases this year seem to be related to that event. But the same warmer climate that has made hurricanes like Ida more powerful is also likely to make diseases like leptospirosis more common here as well.
“The bacteria may persist in warm moist environments. Changes in climatic conditions that allow the bacteria to persist (warmer and moist climate conditions), could contribute to an increase in human cases,” a health department spokesperson told Gizmodo in an email.
New Yorkers are being told to report rat infestations to 311, while they and medical providers should keep an eye out for suspected cases. A full rundown of symptoms and tips to avoid the disease can be found here.