In a late September advisory, the city's Department of Health and Mental Hygiene reported that 14 cases of human leptospirosis had been identified this year, a number it said was more than the total number reported to the city's health department in any previous year.
Cases had been identified in all boroughs except Staten Island with "no obvious clustering."
Thirteen out of the 14 people were hospitalized with acute renal and hepatic failure and two of the patients reportedly also had severe pulmonary involvement.
One person died as a result of infection and all others were treated and discharged.
Three of those infected were reported to be experiencing homelessness and one person was traveling when infected.
Most of the cases had a "clear history or risk factor" that exposed them to an environment with a severe rat infestation, the advisory noted.
A health official reportedly told Insider that there was a 15th case of the zoonotic disease last week and that the person infected appears to have recovered.
The department's Division of Disease Control Deputy Commissioner Celia Quinn noted that the health department had been conducting inspections and working with property owners to conduct rat remediation.
Last May, the U.S. Centers for Disease Control and Prevention (CDC) warned that rats were likely to become more aggressive due to the impact of the COVID-19 pandemic.
The department said New York City has documented a total of 57 cases between 2006 and 2020.
In 2017, a Bronx neighborhood was targeted by the health department after one person died and two others became severely ill from leptospirosis, including a man with the first documented case of testicular swelling associated with the disease.
Animals and pets can also fall ill and New York issued a veterinary medical alert that same year.
The Big Apple is home to millions of rats and placed third on Orkin's list of America's "Rattiest Cities," behind Chicago and Los Angeles.
According to the CDC, leptospirosis infection in humans happens through contact with urine from infected animals or other bodily fluids – with the exception of saliva – or contact with water, soil or food contaminated with the urine of infected animals.
Symptoms of the disease include high fever, headache, chills, muscle aches, vomiting, jaundice, red eyes, abdominal pain, diarrhea and a rash. However, some people may experience no symptoms at all.
The time between a person's exposure to the contaminated source and becoming sick ranges from two days to four weeks.
After the first phase of the disease, the patient may recover but become ill again and the second phase is more severe, leading to kidney damage, meningitis, liver failure, respiratory distress and death.
The illness lasts anywhere from a few days to more than three weeks and recovery could take several months without treatment.
Leptospirosis is treated with antibiotics, such as doxycycline or penicillin, which should be given early on in the course of the disease.
People can reduce the risk of acquiring the illness by not swimming in contaminated water or eliminating contact with potentially infected animals.
The agency noted that leptospirosis is most common in temperate or tropical climates and that incidence of leptospirosis infection among urban children appears to be increasing.
The Associated Press contributed to this report.