The New York City Council unanimously passed legislation Thursday regulating cooling towers, the kind the government blames for the city's worst-ever Legionnaires' disease outbreak that has killed 12 people and sickened 109 others.

By a vote of 42-0, lawmakers sent a bill to Mayor Bill de Blasio's desk that requires a building owner to register a tower with the city, test it quarterly, and if the results are positive for Legionella bacteria, disinfect the tower.

The towers are now mostly unregulated. The de Blasio administration has acknowledged having no precise count on the number of towers but has said the number is at least 2,500.

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Speaking Thursday at Lincoln Medical Center, a South Bronx hospital that has treated many of the infected patients, de Blasio said he expects to sign the bill Tuesday -- the soonest possible time he can legally do so.

Violators face maximum punishments of $25,000 or a year in jail. The council's leader, Melissa Mark-Viverito, said bill drafters included strict penalties "because of the potential here" for people to get sick.

The mayor said 121 people have been diagnosed with Legionnaires' disease since the outbreak began in early July.

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The investigation into the outbreak's source has focused on the South Bronx. There have been no new diagnoses since Aug. 3, de Blasio said.

A prisoner at Rikers Island was diagnosed recently with the treatable bacterial pneumonia but the city said a DNA test showed the case is unrelated to the South Bronx flare-up.

The law would supplement an interim order issued Aug. 6 by city Health Commissioner Dr. Mary Bassett that mandates testing of every cooling tower in the city.

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Bassett said she expects laboratory test results within days that will answer questions including whether the bacteria in the contaminated cooling towers are linked.

The city legislation on registering cooling towers and setting standards for testing and disinfecting "will form the basis" of statewide regulations to be announced by Gov. Andrew M. Cuomo, de Blasio said.

"The state liked the model that was being developed between the mayor's office and the City Council," de Blasio said, adding: "It was very helpful to have all those brains around the table."