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Lake Advisory Remains in Effect

Chemical Results Confusing

and Monitoring to Continue

By Lake Wildwood Administration

 

We received a number of updates late last Friday pertinent to the Lake. Let me say at the outset that solving this problem, and finding out exactly what made all of these people sick, and being assured that our Lake is safe, is a complex and lengthy process. We hope the following brings you up-to-date on the science of solving this problem. The bottom line is that it is too early to answer these difficult questions and reopen the Lake.

First, testing in the area of the August 13 sewage spill showed that E. coli levels in the upper end of Lake Wildwood Creek bay had decreased to very low levels, with all sample points measuring 4 E. coli per 100 mL or below. The EPA recreational limit we use as guidance is a single sample maximum of 235 per 100/ mL. Postings related to the sewage spill were removed, but the general “No Swim” advisory due to the E. coli O157:H7 outbreak remains in place.

In our last update we reported that the Placer County Health Department (PCHD) lab had not detected E. coli O157:H7 in water or scat samples, but using genetic testing they detected shiga toxin genes, but not related to E. coli O157:H7. It was emphasized that these results were considered “Preliminary”. PCHD reported last week that they had not been able to confirm the preliminary test results.

Scat samples had also been submitted to the California State Health Department Lab (CDPH). In addition, 50-liter concentrated water samples from Commodore Beach and Meadow Park Beach, and a wet sand sample from along the shoreline at Commodore were shipped to Centers for Disease Control (CDC). Preliminary reports from both labs were received late Friday evening.

CDPH analyzed 3 goose scat samples and 3 deer scat samples. They reported they isolated E. coli O157:H7 from one of the goose scat samples. The isolate possessed the shiga toxin 2 gene (stx2). There are two genes commonly associated with shiga toxin production, stx1 and stx2. The other two goose samples and the 3 deer scat samples were negative for E. coli O157:H7. CDPH is still in the process of conducting strain typing to determine if the E. coli O157:H7 strain isolated from the goose scat is the same strain isolated from the infected children and adults. We do not know that yet. We also do not know how widely distributed the E. coli O157:H7 bacteria is in our goose population. Three samples is too small a sample size for a reliable assessment.

CDC reported they were not able to isolate E. coli O157:H7 by standard culture procedures from the 50-L concentrated water samples or the wet sand sample. They did detect genes specific for E. coli O157:H7 and the stx2 gene in the Commodore sand sample and the 50-L water sample from Meadow Park. The stx1 gene was not detected. CDC recommended that further testing be conducted using microbial source tracking techniques (genetic “finger printing”) to determine if the indicator E. coli that are being detected in the shoreline beach samples can be traced to specific animals.

Our routine lake E. coli monitoring continues to show the same pattern we’ve reported. All samples from the beach swim zones at waist deep water and at the rope-line are well below the recreational limits. Both the County testing and our own testing detect sporadic high counts at the shoreline. Recent data suggests those shoreline high counts may be dropping, but it is too soon to tell if that is a significant trend or just random. At this time the No Swim Advisory remains in place.

Our County Health Department and Environmental Health staff are planning a conference call with CDC and CDPH this week to discuss the next steps in the investigation and what criteria should be used for reopening the beaches for swimming. Detecting E. coli O157:H7 in the one goose scat sample may complicate that assessment.

We caution again, this is still an ongoing investigation. The data are not conclusive yet regarding the source of the E. coli O157:H7 outbreak. We are getting some hints, but it would be inappropriate to draw any final conclusions at this point. We understand the importance of this issue to the entire community and will keep you updated as we learn more.

 


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