Last week, Baltimore city officials announced that extremely low-levels of a microscopic parasite were found in a city drinking water reservoir. The contamination affects roughly half of Baltimore City along with parts of Baltimore and Howard counties.

Out of an abundance of caution, the city is telling residents who are elderly, small children or immunocompromised to boil their water before drinking or stick to bottled water. According to the Centers for Disease Control and Prevention that includes people with HIV/AIDS, some inherited immune diseases and cancer or liver treatment patients who may be taking certain immunosuppressant drugs.

According to city officials, no one has yet reported an infection to the city or been hospitalized.

Richard Luna, interim director of the Department Public Works, told reporters at an unrelated press conference on Monday morning that DPW is conducting additional testing. Samples were taken from Druid Hill Reservoir last week and sent out to an independent laboratory for analysis, Luna said he expects the results to be back on Wednesday.

Marcia Collins, chief of Legislative Affairs for DPW, stressed to WYPR in an interview that the amount of cryptosporidium detected in the reservoir is “extremely low.”

“You have the ability to test to certain levels and this is at the very lowest part to detect anything. So you can detect its presence, but it's extremely minute,” she said.

There are different kinds of cryptosporidium and according to Collins, the department does not yet know which kind is contaminating the reservoir. The cause of contamination is still under investigation.

The Druid Hill Reservoir is uncovered; the Environmental Protection Agency has ordered the city to cover that reservoir and the one in Ashburton by the end of 2023 but the city has repeatedly missed federal deadlines to complete those projects in the past.

“One possibility is because of the rains, there was a lot of [water] washed into it… it's just very hard to pinpoint where it's coming from,” said Collins. The parasite could have entered the water system through overflow but it’s also spread through animal feces.

What is cryptosporidium and what does it do? 

Cryptosporidium is a microscopic parasite typically found in rivers and lakes. Natalie Exum, an environmental scientist at the Johns Hopkins Bloomberg School of Public Health says the parasite can cause severe gastric distress like watery diarrhea, stomach cramps and even fever. She says that infection has “an average of seven days.”

“So this isn't just like a quick thing that you get over the next day, this is a meaningful enough episode of diarrhea that you’re going to notice it,” she said. Dehydration is the biggest concern when it comes to diarrheal infections, she explained.

It can spread person to person so caution and proper hygiene need to be taken, especially in the bathroom around fecal matter. Exum stresses the importance of hand washing and wiping.

The Baltimore City Health Department is looking for cases of cryptosporidium infection related to the drinking water so Exum recommends contacting your doctor if you have diarrhea that doesn’t clear up within one day.

“It is in both your interest and the community's interest to contact your medical provider and see if they want to get a stool sample from you and test to see where that infection is coming from,” she recommended.

The parasite is tolerant to chlorine, which is used in most water treatments. That’s why those at most risk should boil their water.

The cryptosporidium was detected during routine water quality testing. Unlike last year’s e.Coli contamination, Exum noted that this contamination is not due to an infrastructure failure.

“This is actually the system working to guarantee that the water coming out of your tap is safe, because that monitoring is so critical… before people get sick,” she said.

According to a weekend news release, “DPW has initiated bottled water delivery to senior centers, senior buildings, nursing homes, and assisted living facilities with 20 or more residents, that are in the impacted area within Baltimore City.”