Authorities now say four buildings at the Melrose Houses NYCHA complex have preliminarily tested positive for legionella, the bacteria that causes Legionnaires' disease.

Officials say four of the nine buildings at the complex returned positive results in a preliminary test for the bacteria. Four people have been diagnosed with Legionnaires' at the Melrose Houses in the past six months.

The buildings are located at 304 E. 156th St.; 346 E. 156th St.; and 320 E. 156th St. Health officials had already reported that another building, located at 681 Cortlandt Ave. also tested positive for the bacteria earlier this week. Authorities say they've already cleaned that building and installed filters in each apartment after one person there was diagnosed with Legionnaires'.

NYCHA crews are now cleaning the other buildings that tested positive at the complex. They say they've shut off hot water at the three buildings, and are installing ionizers to get rid of the bacteria.

At its peak, the Legionnaires' outbreak in the Bronx swelled to 128 cases and caused 12 deaths, according to health officials.

Authorities are urging anyone who experiences flu-like symptoms to see a doctor immediately.