NEW YORK (Reuters) - New York City's historic Opera House Hotel, identified as the source of a deadly spate of Legionnaires' disease, said it will go beyond newly imposed regulations in testing its cooling system even as officials declared an end to the outbreak.

City officials on Thursday announced an end to the outbreak, which killed 12 people and sickened 128 people. Of those, two had been guests of the South Bronx hotel, according to the New York City Department of Health and Mental Hygiene.

Health officials matched the strain of Legionella bacteria found in the hotel cooling tower with the strain found in Legionnaires' patients, the department said.

The hotel's cooling tower and all other cooling towers in the affected area were disinfected, and no new patients have contracted Legionnaires' since Aug. 3, city officials said. Health experts are still locating and testing all cooling towers in the city, they added.

New York City Mayor Bill de Blasio this week signed an unprecedented law regulating cooling towers throughout the city, requiring building owners to inspect all towers quarterly and to report and disinfect towers with dangerous levels of bacteria.

The Opera House Hotel said as an extra precaution, it will test its cooling tower every 30 days when the tower is in operation.

Legionnaires’ disease, a severe form of pneumonia, is caused by inhaling mist infected with the bacteria Legionella. Symptoms include fever, cough, chills and muscle aches.

"Given recent events, we have decided to be especially cautious going forward," the hotel said in a statement on Thursday, adding that new tests completed this week confirmed the hotel's tower is clear of the bacteria.

"It's particularly disappointing because our system is two years old, has the most up-to-date technology available and our maintenance plan has been consistent with the regulations that both the city and the state are putting in place," the hotel said.

The hotel was formerly the Bronx Opera House, which opened in 1913 and hosted entertainers, including the Marx Brothers comedians and illusionist Harry Houdini.

(Reporting by Katie Reilly; Editing by Barbara Goldberg and Susan Heavey)