A deadly bacterial infection has killed two people in New York City

A bacterial infection that primarily attacks the lungs has broken out in New York.

So far, the deadly outbreak has killed two people and sickened 31. It's currently under investigation in the South Bronx section of New York City, health officials said on Wednesday.

The new wave of Legionnaires' disease, a type of pneumonia caused by bacteria, has been recorded since July 10, the city's health department said in a statement.

Legionella, the bacteria that causes Legionnaires' disease, is mainly spread through water, which means it's typically not passed between people. Instead, the bacteria lives in certain plumbing systems, including hot tubs, humidifiers, cooling towers and hot water tanks.

It was double the number of cases recorded in the last outbreak, in which 12 people in the Bronx fell ill in December 2014. The cause was traced to contamination in cooling towers at Co-op City, the world's largest cooperative housing development, according to the health department.

The health department said it was testing water in the area to determine the cause of the outbreak. Symptoms for Legionnaires' include fever, cough, chills and muscle aches.

"We are concerned about this unusual increase in Legionnaires' disease cases in the South Bronx," Health Commissioner Mary Bassett said in a statement.

Legionnaires' disease can be treated with antibiotics, but if left undiagnosed, it can lead to death as is the case with this outbreak.

"We are conducting a swift investigation to determine the source of the outbreak and prevent future cases. I urge anyone with symptoms to seek medical attention right away," she said.

(Reuters reporting by Katie Reilly; Editing by Barbara Goldberg and Doina Chiacu)