9 Howard schools test positive for bacteria Legionella, results show

Nine Howard County schools tested positive for the bacteria known as Legionella last month, according to results posted in a school system announcement Friday.

“Out of an abundance of caution and based on industry best practices, [the Howard County Public School System] began proactively testing for the bacteria Legionella in September 2019,” the news release says.


Exposure to Legionella bacteria can cause Legionnaires’ disease, a “serious type” of pneumonia, and a less serious illness called Pontiac fever, according to the Centers for Disease Control and Prevention.

Occurring naturally in freshwater environments, such as lakes and streams, Legionella “can become a health concern when it grows and spreads in human-made building water systems,” according to the CDC.


According to the school system, it is “not uncommon to find various Legionella species in building water systems. There are at least 50 Legionella species, only 20 of which cause human diseases.”

The school system tested all schools and buildings with cooling towers. Twenty-three schools and the Department of Education building have cooling towers.

When the genus Legionella is detected at elevated levels, above 100 colony-forming units, additional treatment and maintenance is warranted, the school system said.

At the high school level, Atholton, Hammond, Howard, Long Reach, Marriotts Ridge, Mt. Hebron and River Hill tested positive for Legionella. Howard had two tests done, one in the school’s ground cooling tower and one in its roof cooling tower, both of which came back positive.


Two elementary schools — Laurel Woods and West Friendship — exhibited positive findings for Legionella. No middle schools came back positive.

Remediation efforts include conducting additional chemical treatment and maintenance, such as super chlorination.

Schools with positive results will communicate with their communities, the school system said.

The school system will test for Legionella annually during the fall, when the water in cooling towers can become idle for an extended period of time due to low cooling load conditions.

Samples were taken from all schools with cooling towers:

  • Atholton Elementary
  • Atholton High
  • Department of Education
  • Centennial High
  • Clarksville Elementary
  • Cradlerock Elementary/Lake Elkhorn Middle
  • Dunloggin Middle
  • Forest Ridge Elementary
  • Hammond High
  • Harper’s Choice Middle
  • Howard High
  • Laurel Woods Elementary
  • Long Reach High
  • Marriotts Ridge High
  • Mt. Hebron High
  • Oakland Mills High
  • Oakland Mills Middle
  • River Hill High
  • Reservoir High
  • St. John’s Lane Elementary
  • Talbott Springs Elementary
  • West Friendship Elementary
  • Wilde Lake High

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