Dozens of additional water-cooling towers on the Upper East Side have tested positive for Legionella, the bacteria that causes Legionnaires’ disease, amid the city health department’s ongoing investigation into an outbreak of the severe form of pneumonia.

The number of building sites affected by the outbreak has more than doubled since initial test results were released late last week.

City health officials released a list of 45 new buildings whose cooling towers tested positive for Legionella bacteria Tuesday evening, adding to an earlier list of 31 sites that was released on Friday.

All owners of the buildings whose towers tested positive have been ordered to drain, clean, and disinfect their buildings to remove the bacteria, city health officials said.

As of Tuesday, 57 building owners had completed the remediation process, and another 19 were ordered to complete it by Thursday, according to the city health department.

Cooling towers were tested in the three ZIP codes affected by the outbreak, stretching from the East River to Central Park: 10028, 10128 and 10075. City officials said Tuesday that the initial testing is now complete. No additional buildings were expected to test positive.

“There is no additional risk associated with being inside one of these buildings,” Dr. Alister Martin, the city health commissioner, said Tuesday.

Identifying and remediating the cooling towers is a step forward in the city’s effort to contain the Legionnaires’ outbreak, which has so far sickened 60 people and sent 49 to the hospital, according to the city health department. No deaths have been reported so far.

But city officials say more testing will be needed to determine which of the buildings’ cooling towers is responsible for the Legionnaires’ outbreak. Legionella bacteria can grow in the water that sits inside buildings’ cooling towers. It is then spewed into the air along with water vapor, which passersby can inhale.

The number of new Legionnaires’ diagnoses has slowed in the affected area in recent days, after peaking on July 6, according to city data. Martin said on Friday that he expected new diagnoses to start tapering off as cooling towers in the neighborhood that tested positive for Legionella were remediated.

Additional buildings that tested positive for Legionella and have completed remediation:

1130 Fifth Ave. 1150 Madison Ave. 1239 Madison Ave. 1275 Madison Ave. 1020 Park Ave. 1157 Lexington Ave. 1755 York Ave. 60 East End Ave. 188 East 78th St. 200 East 78th St. 124 East 79th St. 201 East 79th St. 211 East 79th St. 511 East 80th St. 444 East 82nd St. 500 East 83rd St. 7 East 86th St. 401 East 86th St. 444 East 86th St. 445 East 86th St. 51 East 87th St. 9 East 90th St. 410 East 92nd St. 40 East 94th St.

Additional buildings that tested positive for Legionella and have been ordered to complete remediation by Thursday:

980 Fifth Ave. 1000 Fifth Ave. 920 Park Ave. 1249 Park Ave. 1025 Madison Ave. 1381 Lexington Ave. 1513 First Ave. 1520 York Ave. 80 East End Ave. 90 East End Ave. 100 East End Ave. 155 East 79th St. 40 East 80th St. 25 East 83rd St. 13 East 84th St. 40 East 84th St. 108 East 89th St. 22 East 91st St. 200 East 95th St. 235 East 95th St.

Unregistered cooling tower that tested positive for Legionella and completed remediation:

300 East 83rd St.