The immunocompromised, young kids and seniors advised to avoid drinking water in parts of Baltimore area after parasite detected

Baltimore City officials are advising immunocompromised individuals, as well as some young children and the elderly, to avoid drinking tap water across a large swath of its service area in the city, Baltimore County and a small part of Howard County due to parasitic contamination.

Testing has detected low levels of a microscopic parasite called cryptosporidium in the drinking water reservoir at Druid Lake in Baltimore, officials announced Thursday.

Vulnerable people in the affected area are advised to boil their drinking water for one minute, to drink bottled water or water sent through filters equipped to remove objects 1 micron or larger.

The affected area stretches across city from southwest to northeast Baltimore, including much of West and North Baltimore, and north and east into Baltimore County, from Towson up through Hunt Valley to Cockeysville and Sparks and including Parkville, Perry Hall and Overlea, according to a map shared by Baltimore City’s Department of Public Works. It also reaches in southwest into Baltimore County to include Arbutus and into Howard County’s Elkridge along Route 1.

Officials said the low concentration of the parasite presents a low risk to the general public, but cryptosporidium can cause gastrointestinal problems, including diarrhea, stomach cramps and nausea.

Therefore, immunocompromised people, including those with HIV/AIDS and cancer, transplant patients taking immunosuppressive drugs and those with other conditions of the immune system, are particularly urged to take precautions. They are more likely to develop severe or life-threatening symptoms, according to the Centers for Disease Control and Prevention.

Young children and the elderly also are more likely to become infected, and the city’s Department of Health advises that “those who attend childcare centers, including diaper-aged children” and those 75 and over should take the precautions, spokesperson Yianni Varonis said.

So far, no cases of cryptosporidiosis, the illness caused by the bacteria, have been reported in the city within the last two months, said Tamara Green, chief medical officer at the Baltimore City Department of Health, during a news conference Thursday.

“For most people, if they have a healthy immune system, they will not have any symptoms,” Green said. “But we want people to be vigilant and monitor their symptoms.”

Cryptosporidium is a leading cause of waterborne illness in the United States, according to the CDC, and high concentrations of the parasite have caused serious outbreaks in the past. In 1993, hundreds of thousands of people were infected with cryptosporidiosis after a malfunction of a city water treatment plant in Milwaukee, Wisconsin, and 69 people died, many of whom were battling AIDS at the time.

“The levels that they found today are much, much lower, compared to these huge outbreaks,” said Natalie Exum, an environmental health scientist at the Johns Hopkins Bloomberg School of Public Health.

The main reason cryptosporidium is concerning is that the parasite is resistant to chlorine, Exum said. That means that the residual amount of chlorine within the drinking water system, which is introduced to kill bacteria, wouldn’t be able to eliminate the parasite.

On Tuesday, the city received the results from a laboratory indicating that samples collected Sept. 19 contained a 0.09 oocycst per liter concentration of the parasite, said Richard Luna, the interim director of the city’s Department of Public Works. The city announced the contamination Thursday morning.

Luna said that the city notified the Maryland Department of the Environment and the federal Environmental Protection Agency on Tuesday, and the agencies have been collaborating on the public communication strategy.

“For us, it’s really important to give you the right information as quickly as possible, but to really look at those communications prior to, so that they’re clear and understandable for the public,” Luna said.

The city also collected follow-up samples Wednesday, but it must wait 5-7 days for the next round of results, Luna said.

The city was heavily criticized last year for what some called a slow response to and announcement of the discovery of E. coli bacteria in tap water in West Baltimore during routine testing. In that instance, the city also took about two days to notify the public.

During Thursday’s news conference, City Administrator Faith Leach drew a distinction between the E. coli contamination and the cryptosporidium contamination. The E. coli contamination resulted in a weeklong “boil water advisory” for all residents in the affected area — not just vulnerable residents — because it was considered more dangerous.

“I don’t want to conflate E. coli with cryptosporidium. These two are completely different things,” Leach said. “The big takeaway ... is that we believe that our drinking water remains safe for the general population.”

Exum said she understands the city taking some time to prepare communications for the general public, especially when the risk is lower than with E. coli contamination.

“You want to be able to tell the full story about why you’re not shutting off the water for the whole city, and saying everyone has to start boiling their water,” Exum said.

It’s possible that the levels detected earlier this month at Druid Lake were a “one-off,” perhaps caused by animal feces reaching the reservoir, Exum said. Future samples will show whether the contamination is more extensive, or whether it has dissapated.

The Druid Lake Reservoir holds water that already has been treated by the city’s facilities, and is later sent to homes and businesses in the city and surrounding counties. Construction crews are working to replace the open-air reservoir with underground storage tanks in an effort to protect the treated water from contaminants.

It’s a project that has been marred by years of delays, and earlier this year, the federal Environmental Protection Agency served the city an order to cover the reservoir, and a second open-air reservoir at Lake Ashburton, by the end of 2023.

The order also included a mandate that the city initiate monthly testing for giardia and cryptosporidium while the reservoirs remained uncovered. That testing began in late July and early August, Luna said. Those initial samples indicated no evidence of contamination.

The raw water from the city’s reservoirs at Loch Raven, Prettyboy and Liberty, which is later treated for contaminants like cryptosporidium, also does not show evidence of contamination, according to a news release from the city.

Luna said the efforts to get the covered water sources online are proceeding according to the EPA-mandated schedule, with the Ashburton project expected to finish by Nov. 30, and the Druid project by Dec. 30.

The levels of cryptosporidium in the water at Druid Lake were “so low that it was even hard for the laboratory analyst to detect” the parasite, Luna said.

“They stated to us that it would be too difficult to pinpoint the exact source,” Luna said.

City officials studied the water system in order to determine all of the possible areas in the city and surrounding counties that could have received the contaminated water, which already would have been distributed by the time the city received the positive result, Luna said.

“Our analyzers looked at all of the modeling data to see: Water that was released through Druid Lake: Where did that end up in our system?” Luna said. “And so overall, that map that you see is probably the largest capture of where that water could have gone.”

The city has yet to announce whether there are plans to distribute bottled water in impacted areas, but that is being “coordinated internally,” Luna said.

City Councilwoman Odette Ramos said she and other members of council whose districts were impacted were notified about the contamination Thursday morning. The council members did not receive a map of affected areas, however, until it was distributed publicly, she said.

”I would have liked to see the map ahead of time, because when people started calling — which is exactly what happened — then we would have had the information,” she said.

Councilman John Bullock, whose district also is impacted, said he felt the communication from the city had improved since last year’s E. coli contamination.

“In the last situation, a lot of us really found out via social media,” Bullock said.

Councilman Ryan Dorsey said Thursday’s announcement “helps us understand some of why our drinking reservoirs are safer if they’re covered up, despite the inconvenience of projects like covering the Druid Lake Reservoir.”

Baltimore Sun reporter Emily Opilo contributed to this article.