Food Engineering

E coli outbreak not surprising

November 1, 2006




According to a recent FDA report, the September 14th CDC-confirmed E coli outbreak affecting 204 people in 26 states was traced back to Monterey County spinach grower and producer, Natural Selection Foods in San Juan Bautista, CA. But contamination is not a new problem for producers of leafy vegetables from this region. In fact, an FDA Update from October 6, 2006 states there has been a long history of E. coli O157:H7 outbreaks involving leafy greens from central California. In its November, 4, 2005 letter to California lettuce growers and packers, FDA cited 18 E coli outbreaks since 1995, of which eight completed tracebacks lead to Salinas, California.

FDA is checking several potential sources for the E coli, which is known to come from cattle feces, but has yet to list a definitive root cause. With cattle ranches nearby the producer, potential sources under investigation by the California Department of Health Services include improper handling of manure as fertilizer, agricultural runoff, stray cattle, and infected irrigation water, the latter of which has been suspect for some years by some government officials. Farms in the area use recycled sewage-derived water for spray irrigation, which is transported in underground pipelines from a public water treatment center.

Although effluent water meets all EPA guidelines, the USDA suspects pathogen "regrowth" in the transmission of the water. A USDA lab study assessed the survival and regrowth potential present in tertiary effluent as it passed through a model distribution system over an 11-day period. It found that population numbers of bacteria increased by three to four orders of magnitude, potentially placing the water out of compliance at its point of intended use.

There have not yet been tests with published results that show bacteria growth on plant leaves when delivered by spray irrigation. The USDA is diligently working on "recycled water" issues but reports several unknowns. "Using present technologies, municipal wastewater treatment may not completely disinfect recycled irrigation waters, allowing pathogenic microbial populations to re-grow in water storage and transmission systems. As a result, recycled water used for agricultural and municipal irrigation can contain enough pathogenic organisms to threaten human health."