Digging Deeper: Was the E. coli Investigation in Big Chico Creek Missing Pieces?

You've probably heard about the E. coli O157:H7 outbreak linked to Big Chico Creek in Butte County. It's a serious issue, and public health officials, including the CDC, have been hard at work trying to figure out where this harmful bacteria is coming from. But what if the investigation, as thorough as it might seem, missed some crucial spots? Let's take a closer look at how they decided where to sample and what they found.

What We Know About the Outbreak So Far

First, the good news (sort of): E. coli O157:H7 was definitely found in the creek's water and sediment at popular spots like Sycamore Pool, the Chico Creek Nature Center (CCNC), and the Five Mile Recreational Area. Even more importantly, the specific type of E. coli found in the creek matched the bacteria that made people sick. This tells us the creek was indeed the source of the outbreak.

To try and pinpoint where the contamination was coming from, scientists used something called Microbial Source Tracking (MST). This technique looks for specific DNA markers that tell you what kind of animal (or human) waste is present. Here's what they detected:

• Avian (bird) fecal marker: This was found in all water and sediment samples.
• Goose-specific DNA marker: This was only found at Horseshoe Lake, an area known for geese. Interestingly, even with goose markers present, no E. coli O157 was detected at Horseshoe Lake or Alligator Hole.
• Ruminant (like cows, deer) fecal marker: This was detected in water from Sycamore Pool, CCNC, and Five Mile, and also in sediment at Five Mile. However, they didn't find any cow-specific markers.
• Human fecal marker: This was also detected in water from Sycamore Pool, CCNC, and Five Mile. This is a pretty significant finding, as it suggests human waste could be contributing to the problem. It is likely either encampments or septic systems.

Officials started sampling downstream and moved upstream to help track the flow of contamination.

Could There Be Selection Bias?

Now, here's where things get interesting and a bit concerning. The way sampling sites were chosen raises questions about whether the investigation truly covered all potential sources.

The sources clearly state that Horseshoe Lake was explicitly selected as a sampling site "due to goose exposure". This makes sense, as geese have been linked to E. coli outbreaks in other places, like the Lake Wildwood incident. The CDC recommended sampling at the three main swimming sites, a location downstream of the golf course, and an upstream area with wildfire sediment.

However, what about other potential sources that might have been overlooked? Our review of the 801 pages of the CPRA response from which these documents were drafted reveals something important: the specific human fecal marker, HF183, is not once mentioned. While the sources do confirm the detection of a "human fecal marker", the absence of the specific HF183 reference leaves some detail out regarding the exact MST methods for human waste.

Even more, while internal discussions acknowledged concerns about "encampments" and "bad septic tanks" as possible factors in the E. coli problem, the provided documents do not include any records identifying proposed, but ultimately not selected, sampling sites that might have targeted these areas or storm drain outfalls. This omission is crucial because if areas with known human activity, like encampments, were not thoroughly investigated, it could create a "selection bias" – meaning the chosen sites might not represent all possible sources of contamination.

The Public Health Officer, Jarett Beaudoin, himself recognized the challenge of Microbial Source Tracking, saying,

"The trouble is, you never really know if the high-volume crappers are the crappers you are looking for".

This highlights how difficult it can be to connect fecal markers directly to the specific E. coli strain causing the outbreak.

Looking Ahead: Towards a More Complete Picture

The genetic analysis indicated a "common, continuous source" for the bacteria, which has yet to be definitively found. There were discussions about potentially doing more animal testing, specifically for deer scat, if the water board investigation hit delays, and Butte County was open to funding this. There were also questions raised about the City of Chico possibly using creek water for irrigation in parks and if this was a risk.

For a truly comprehensive understanding of the E. coli problem in Big Chico Creek, it's vital that all potential sources are considered and openly investigated. Transparency in site selection and thorough documentation of all samples and results are key to building public trust and finding lasting solutions to keep our recreational waters safe.