Epidemiologist: Baker City crypto outbreak historic

Written by Jayson Jacoby August 06, 2013 09:16 am

By Jayson Jacoby

This e-mail address is being protected from spam bots, you need JavaScript enabled to view it

Baker City’s cryptosporidium outbreak is historic, and possibly in more ways than one.

Dr. Bill Keene, senior state epidemiologist with the Oregon Health Division, said Monday afternoon that if the city’s water is definitely proved to be the source of the rash of illness — and that’s the most plausible theory, he said — then this probably would be the largest outbreak in a municipal water system since a 1994 episode in Las Vegas.

“It’s a significant outbreak,” Keene said. 

Most of the confirmed crypto cases in the U.S. over the past 20 years — there were 7,656 confirmed or probable cases in 2009, and 8,951 in 2010 — were linked to sources such as swimming pools and daycare centers, not municipal drinking water, according to the federal Centers for Disease Control and Prevention.

If another theory about the Baker City outbreak pans out — that the crypto source was feces from mountain goats that live near Goodrich Reservoir — that likely would be the first such case in crypto annals, at least in the U.S., Keene said.

“I’m pretty sure mountain goats have never been tested (for crypto),” Keene said.

The parasitic protozoa is commonly found in wild animals as well as in domestic cattle, he said.

 

Although cattle graze on Forest Service and private land near the city’s 10,000-acre watershed in the Elkhorn Mountains, about 10 miles west of town, City Manager Mike Kee said water department employees who surveyed the watershed last week found no evidence that cattle had been roaming in areas where the city diverts water from streams into its supply pipeline.

Although crypto “oocysts” were found in city water samples taken on July 31, the numbers were lower than what would likely be necessary to cause widespread infections among people, Keene said.

The largest number in a single water sample was 3 oocysts. Some studies have shown than as few as 10 oocysts can cause illness in a person, although people's susceptibility to crypto varies widely. Many people don't have any symptoms even when they have been infected. Those people can, however, spread crypto through their feces. 

(The oocyst is the protective shell that makes crypto resistant to the chlorine the city adds to its drinking water to protect against other bugs, such as giardia.)

He believes that at some point a large number of oocysts entered the city’s water supply. For perspective, a single bowel movement from a human can contain millions of oocysts, according to lab tests.

Keene said such crypto “flushes” have been attributed in other outbreaks to heavy rain that washed crypto-infected feces or soil into a water source.

“Is that what happened here? At this stage we don’t know for sure,” Keene said.

The heaviest rainfall near Baker City this year happened on June 19, when a record 1.57 inches fell at the airport.

There is no rain gauge at Goodrich Lake, but snow fell in the mountains, including at Goodrich’s 6,871-foot elevation, during the June 19 storm.

Keene said crypto “has been around forever,” and that small numbers of oocysts likely are present in most surface water.

But given the rarity of outbreaks caused by municipal water supplies — including ones, like Baker City’s, that use unfiltered surface water — it seems that Baker City’s ordeal could be “the exception proving the rule,” he said.

A complicating factor is that there are at least 22 species of crypto, and not all of them are known to make people sick. Ninety percent of cases in humans are caused by either of two species, according to a 2012 article in the journal "Tropical Parasitology"

According to a 2004 article in Clinical Microbiology Reviews, crypto species "originating from wildlife... are mostly not human pathogens." 

Although federal statistics show a sharp increase in crypto cases starting in the 1980s, Keene said that trend likely reflects more widespread testing rather than an actual spread in crypto.

Until the 1980s crypto tests were rare, and they required a high level of expertise.

What helped to bring the bug into the mainstream, so to speak, was the AIDS epidemic of the 1980s. Because AIDS patients have severely compromised immune systems they are especially vulnerable to crypto.

“People were dying from this,” Keene said.

Today, crypto tests are easier and more effective, and doctors and other officials are much more likely to suspect crypto than they used to be, he said.

Speaking of tests, Keene said the “official” count of 14 crypto cases in Baker City certainly doesn’t reflect the total number of infections.

That’s almost always the case in outbreaks, he said, because with otherwise healthy people the infection usually doesn’t cause symptoms that require medical attention, so relatively few people ever have stool samples tested.

That’s one reason the CDC compiles lists of both confirmed and probable cases of crypto infection.

Keene, who was in Baker City for several days before returning to his Portland office on Monday afternoon, said he and colleagues visited 21 Baker City homes and talked with 62 residents.

Of those, 18 had had symptoms consistent with crypto, Keene said — 29 percent of the total.

Keene said he wouldn’t conclude from that small sample size that one-third of residents were infected — that would be almost 3,000 people — but he said the total cases “could easily be in the hundreds.”

He said he hopes to have more door-to-door surveys, as well as phone interviews, conducted soon.