Cases of Leptospirosis Have Surged in New York City—What to Know About This Infectious Disease Spread by Rats

New York City's health department has reported an unusually high number of cases of a rare and potentially fatal bacterial disease often spread by rats.

As of late September, the city has seen 14 cases of leptospirosis (also known as Weil's disease) in 2021, according to an advisory issued by the New York City Department of Health and Mental Hygiene, with one confirmed death from the disease.

While that doesn't sound like a lot, the department points out that it's more than the total number reported to the agency in any previous year. City health officials only have 57 cases of leptospirosis on record between 2006 and 2020, with up to seven cases reported each year. This year, "cases have been identified in all boroughs except Staten Island, with no obvious clustering," the health department advisory says.

Thirteen of the 14 people were hospitalized with kidney and liver failure, and two of them had lung issues as well. Aside from the person who died from the infection, all of the hospitalized patients were treated and discharged.

The people afflicted with leptospirosis didn't necessarily catch the disease out of the blue. "One person acquired their infection while traveling," the advisory stated. "Among the thirteen locally acquired cases, most cases had a clear history or risk factor which exposed them to an environment with a severe rat infestation. Three cases reported homelessness."

Symptoms of leptospirosis tend to be flu-like and can be confused with many other health conditions, which is why New York City public health officials are urging health care providers to be on the lookout for the disease.

Never heard of leptospirosis before? Though cases appear globally, it's rare in the US. Still, whether you live in New York City or not, you're probably curious about this infectious disease and whether you're at risk. Here's what you need to know.

What is leptospirosis?

Leptospirosis is a zoonotic disease, which means it can spread from animals to humans. It's caused by bacteria of the genus Leptospira and can spread through the urine of an infected animal, according to the Centers for Disease Control and Prevention (CDC). Leptospirosis can be transmitted by many different animals, including dogs, cattle, pigs, horses, and other wild animals. New York City public health officials are pointing the finger at rats in the particular cases identified there.

How do people get leptospirosis?

People can become infected with leptospirosis after having direct contact with urine or other bodily fluids from infected animals, or contact with water, soil, or food that's been contaminated by an infected animal. If a person gets the bacteria in their eyes, nose, mouth, or through broken skin like a cut or scratch, they can develop the disease.

What are the symptoms of leptospirosis?

People can become sick anywhere from two days to four weeks after they've been exposed, according to the New York City Department of Health and Mental Hygiene. Some people have no symptoms, while others may experience symptoms that mimic a cold or the flu, such as the following:

• Fever
• Headache
• Chills
• Muscle aches
• Vomiting
• Diarrhea
• Red eyes
• Jaundice (yellow skin and eyes)

In rare situations, people can develop kidney failure, liver failure, meningitis, which is inflammation of brain and spinal cord membranes. As in one of the New York City cases, the disease can be fatal.

How is leptospirosis treated?

Leptospirosis is treated with antibiotics like doxycycline or penicillin which, ideally, are given earlier on in the infection, per the CDC. People with more severe symptoms will need IV antibiotics, though, the agency says.