When a bacteria is everywhere, how do you find the source of an outbreak?

That’s the challenge facing Multnomah County Public Health. An outbreak of Legionnaires’ disease has sickened at least 13 residents of Rosemont Court, a Portland affordable housing project for seniors, since January. One has died.


The outbreak prompted the evacuation of the entire building. Almost 100 seniors were relocated to hotels while Northwest Housing Alternatives, which runs Rosemont Court, worked to stop the outbreak

Legionnaires’ disease is waterborne and, when inhaled, infects peoples’ lungs. Multnomah County health officers and Portland Water Bureau staff worked with the nonprofit to empty water lines, add chlorine and a disinfecting system, and install filters to showerheads and faucets.

But it didn’t work.

Residents moved back into the building in early March, “and unfortunately since then, we’ve now had our third confirmed case of Legionella in a Rosemont resident,” said Dr. Jennifer Vines, lead health officer for Multnomah County and neighboring counties. Northwest Housing Alternatives is now relocating residents who want it to different housing.

Legionella pneumophila, the bacteria that causes Legionnaires’ disease and Pontiac fever, is found just about anywhere there is fresh water. It is very likely that every person has, at some point, inhaled this bacteria and been none the wiser. A few might catch Pontiac fever, which is a mild, flu-like illness.

But when it’s inhaled by someone who is immune-compromised, or has lung disease, or who is elderly, the bacteria can cause Legionnaires’ disease, a quick-moving lung infection with a 10% fatality rate.

That means you often don’t know there is a risk of Legionella until it’s too late.

”When you find out you have a problem because someone is very ill, you don’t want to be in that position,” Vines said.

Killing hay in a haystack

Back in January, a case of Legionnaires’ was found in a resident of a building near Rosemont. But authorities were never able to connect it to the Rosemont Court outbreak.

”We worked with the Portland Water Bureau, the Oregon Health Authority, and the Centers for Disease Control. It’s really difficult with a bacteria that’s just naturally found in the environment,” Vines said.

That’s the problem — Legionella is present in low levels in most fresh water. So techniques usually used to look for a bacteria aren’t very effective; how do you distinguish between a false and real positive?

“Water samples can be tricky to interpret for that reason,” Vines said.

Similarly, the presence of the Legionnaires’ bacteria in a water system doesn’t mean people, even those who are immune compromised, will get sick. Our bodies are inhospitable places for bacteria, so you usually need to inhale a lot to get infected.

Legionella outbreaks occur when water stagnates, like it sometimes does in rarely-used pipes, and the bacteria start to form colonies. Eventually, chunks of the colony can slough off, travel through pipes, and be dispersed through the air by faucets and showers. Kill the colony, and presumably, the outbreak will stop.

But these colonies, called biofilms, are incredibly hard to kill. Bacteria use biofilms to survive in all sorts of harsh environments. The biofilms form layers, and bacteria in it will share resources. Some, on the outer edge, might die — sacrificed for the common good. Many of the most common ways to sterilize pipes fail against biofilms, given the right circumstances: if a chlorine treatment only kills the top layer of the colony, it won’t take long to regrow. The biofilm can also protect the bacteria from drying up when pipes are drained. And they give the bacteria a place to grow in fast-moving water.

The colonies are even harder to kill when you can’t find them. Things like disinfecting systems are useless if the colonies live downstream. And in order to remove bacteria by fixing the plumbing, you need to know which pipes to replace.


That’s why, at Rosemont Court and elsewhere, point-of-use filters attached to faucets and showers have become the go-to solution for Legionella-caused illnesses.

But those filters can slow water pressure and make it hard to use.

”The three more recent cases look like maybe an improper use of filters could have been a part of it,” Vines said, stressing that she wasn’t placing blame on the people who got sick. Water is an important tool, and “we certainly heard frustration from residents who had bad experiences with the filter slowing flow.”

It’s unclear if that led people to use the filters improperly, said Vines, but she has been working with Rosemont Court’s maintenance team to install filters with a higher flow in apartment units in the building where people have chosen to stay.

A growing problem

Single cases of Legionnaires’ disease aren’t terribly rare. But outbreaks are less common.

”This is the first one I’ve worked on,” Vines said.

An outbreak requires two things: a lot of vulnerable people and a lot of bacteria. Outbreaks often occur on cruise ships. Water can be stagnant when a room isn’t occupied, and cruise ships often have an older population.

But while advances in vaccines and water treatment have caused other diseases to decrease, Legionnaires’ disease has become the most common waterborne illness in the United States. For a decade, Legionella bacteria have accounted for 60% of all outbreaks of water-borne diseases.

And because Legionnaires’ disease responds to the same antibiotics most commonly used to treat pneumonia, cases are only reported if a doctor thinks to test for Legionella. In 2018, the CDC counted 10,000 cases of Legionnaires’ disease in the United States. And another study estimated that the true number of cases could be 1.8 to 2.7 times higher than the official count.

Chris Edens, an epidemiologist with the Center for Disease Control and Prevention, told Smithsonian the increase was likely due to a combination of factors, including aging populations and aging infrastructure.

Rosemont Court, which used to be a girls’ industrial school and has a wing listed on the National Historical Register, has both.

According to a 2016 Portland Water Bureau article, “approximately 20 percent of pipes with known ages in our system are 100+ years old. The average age of our pipes is 64.”

Looking forward

Giving residents the option to relocate was a last resort. But with infections continuing despite mitigation efforts, it became necessary.

“People truly love their homes, their neighbors, and the community at Rosemont Court,” said Trell Anderson, executive director of Northwest Housing Alternatives, in an email. “Yet they understand this prudent next step.”

Vines echoed that sentiment: “I got to talk to a handful of people. It’s a gorgeous building, people there really help each other out, there’s a real sense of community.”

And relocating those who choose to leave is difficult. “The affordable housing market is really tight, which is why we will be calling on our partners to ensure residents find safe and affordable housing options,” Anderson said.

Then, Northwest Housing Alternatives needs to find housing that fits residents’ specific needs, transfer rent assistance to the new property, make sure they are connected to disability services, and coordinate the move.

And some, of course, have chosen to stay and try out the new filters.

“It’s easy to take water for granted when it’s clean and comes out at the temperature you want,” Vines said. “I think we’re on a good path with these new filters. I really hope they work well, so we can do right by these residents.”


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