The iconic Guggenheim Museum is among 31 Upper East Side buildings where water-cooling towers have tested positive for Legionella — the bacteria that causes Legionnaires’ disease — amid the city’s ongoing investigation into an outbreak of the severe form of pneumonia, the city health department said Friday.

The Guggenheim, at 1071 Fifth Ave., and owners of 18 other properties have already completed the process of cleaning and disinfecting their water-cooling towers to rid them of the harmful bacteria, according to the city health department.

Dr. Alister Martin, the city health commissioner, said at an afternoon press briefing that the remaining cooling towers that tested positive will be remediated by Saturday.

“What we are doing is going to the source [of the outbreak] and taking that off the map,” Martin said. “When that happens, my expectation is, that is going to cause the resolution of this cluster.”

The release of the test results represented the closest city has come to pinpointing the cause of the outbreak. The city has tested 183 cooling towers on the Upper East Side for Legionella bacteria since identifying an outbreak of Legionnaires’ disease in the neighborhood on July 2, city health officials said.

Since then, 46 people have tested positive for Legionnaires’ disease and 22 have been hospitalized in the ZIP codes 10128, 10028 and 10075, stretching from Central Park to the East River. No deaths have been reported.

Allegra Thoresen, a spokesperson for the Guggenheim, emphasized in a statement on the museum’s positive test that the city’s investigation into the source of the outbreak is ongoing.

“The Guggenheim continues to follow all New York City cooling tower requirements and regulations using third party expert companies, as we always do,” Thoresen said.

With rare exceptions, the 31 properties identified by the city are high-end residential dwellings, some with ground-level retail. Seven people died in an Legionnaires' disease outbreak last summer in Central Harlem.

City health officials say the cluster of cases on the Upper East Side is likely linked to a cooling tower emitting mist containing Legionella bacteria, and Martin said remediating the towers that tested positive should cut off the source of the outbreak.

But he said he expects that more people will still test positive for Legionnaires’ disease in the coming days before cases start to taper off. Symptoms of Legionnaires’ can take up to two weeks to show up after exposure, according to the U.S. Centers for Disease Control and Prevention.

City health officials emphasized that people living in a building with a cooling tower that tested positive for Legionella are not more likely to get sick. They said anyone in the three ZIP codes that have been identified could have been exposed to Legionella bacteria since the end of June.

Martin said more testing will be required to narrow down which cooling towers are responsible for the outbreak, since the initial PCR tests that were conducted this week capture both live and dead bacteria.

He said the city will now conduct culture analyses to identify live bacteria and then use whole-genome sequencing to try to match the strains found in the cooling towers to those found in people who tested positive for Legionnaires’ disease. That process could take weeks, according to the city health department.

In a letter to Martin earlier this week, City Council Speaker Julie Menin criticized the health department’s approach. She said the city should have ordered the owners of all buildings with cooling towers in the affected area to clean them proactively, instead of waiting for testing results to come in.

Chantal Gomez, a spokesperson for the city health department, said in response that the city had been “aggressively identifying cooling towers that test positive for the presence of Legionella bacteria and ordering building owners to clean and disinfect.”

City health officials are urging anyone who lives on the Upper East Side or has visited since late June to visit their doctor if they experience symptoms of Legionnaires’, including shortness of breath, cough, fever, fatigue or gastrointestinal issues.

This story has been updated with additional information.