The latest batch of four Baker City water samples did not contain crypto, according to the city.
The city also received test results from feces samples of mountain goats, elk and cattle.
A key aspect of the crypto investigation is trying to link the species of crypto - there are more than 20 - that infected local residents, with any crypto found in feces or in water samples, Dr. Emilio De Bess, Oregon state epidemiologist, said this morning.
Of the seven human stool samples tested from local residents who were sick, all seven contained a crypto species called parvum, and all seven also had the identical genotype, De Bess said.
None of the animal feces samples tested so far contained that species of crypto, De Bess said.
Of 81 goat feces samples tested, one was positive for a species of crypto called ubiquitum.
Of 64 elk feces samples tested, one was positive for crypto, but the species was not definitely identified. It was not, however, either the parvum or hominis species, which are the ones most commonly responsible for outbreaks in people.
Of the four cattle feces samples tested, all were negative for crypto.
However, De Bess noted that there were far fewer cattle feces samples - four - than elk or goat samples. He said he collected only cattle feces samples that were "fresh" and thus most likely to have active crypto oocysts (the organism can survive for several months in certain conditions).
That none of the four cattle feces samples contained crypto does not mean cattle weren't the source of the crypto outbreak, De Bess said.
In fact, statistically speaking cattle are a more likely source than are elk, mountain goats and other wildlife. The reason, he said, is that the parvum species of crypto, the species that caused the illness in Baker City residents, is very common in cattle.
When the parvum species is found in people, De Bess said, researchers tend to ask "where are the cows?"
If feces samples from, say, 80 cattle were tested, it's very likely that at least some would contain crypto, De Bess said.
"We know crypto parvum species is correlated to cattle," De Bess said. "That's the only conclusion we can make. Beyond that we can only hypothesize."
Besides feces samples, it's also possible to test water samples for crypto and, if oocysts are present, to pinpoint the species and genotype.
The key sample in Baker City's case was a10-liter sample, taken from Elk Creek on Aug. 4, that contained 913 oocysts. No other water sample from Baker City has contained more than three oocysts.
Elk Creek is the only water source in the city's collection system that has an active cattle-grazing allotment adjacent to the site where the city diverts water into its pipeline.
The city has not used Elk Creek water since Aug. 7, the day the city received the test result showing 913 oocysts.
The city was using Elk Creek water during July, when the first cases of crypto were confirmed in city residents.
De Bess said the Elk Creek water sample was tested to determine whether crypto was present, and if so, how many oocysts. In preparing the slides needed to do so, the oocysts were in effect destroyed, he said, making it impossible to determine the species and genotype.
He said it would have been possible to preserve some oocysts for a more detailed analysis, but that the goal at the time, in early August, was to determine whether Elk Creek and other water sources were safe to use.
"Hindsight is 20/20," De Bess said.
The city could try to work with CDC to have another sample of Elk Creek water tested to determine whether there's any crypto and, if so, its species and genotype.
"We have talked about doing that," De Bess said.
Check back to www.bakercityherald.com, and see Wednesday's issue of the Baker City Herald, for more information about the latest test results.