Four years ago, there were almost no recalls of beef for E. coli O157:H7 contamination and later the federal Centers for Disease Control and Prevention in Atlanta reported on a big drop in illnesses from the pathogen.

Just a year later, in 2007, the number of E. coli O157:H7 recalls, outbreaks, and illnesses exploded.   Beef recalled for E. coli O157:H7 contamination totaled almost 34 million pounds in 2007.

The spike in E. coli contamination sent regulators, researchers, and the industry all out looking for the cause.  Just over 7 million pounds of recalled beef was added to the total in 2008 to bring the total to over 40 million for just two years.

Then last year, the levels fell back to Earth with just over 1.1 million pounds of E. coli-contaminated beef recalled in 2009.

That brings us to 2010.  On one hand, this year’s total beef recalls for E. coli total over 6.1 million to date, bringing the four-year total to over 48 million pounds.

However, the largest recalls in this year’s total were for 5.764 million pounds of beef from California’s Huntington Meat Packing Co. last Jan. 18 and Feb. 12.  At the time, USDA’s Food Safety and Inspection Service (FSIS) said the Huntington recalls were associated with an ongoing criminal investigation.

Since the big Huntington recalls last winter, there have only been another half dozen E coli-related recalls totaling 389,476 pounds of beef and bison.  Only 105,476 pounds have been recalled this summer, including 66,776 of bison from Colorado’s Rocky Mountain Natural Meats.

E. coli O157:H7 knows no season, but is a season-peaking phenomenon.  Food safety attorney Bill Marler knows this not only from his law practice, but from the research he has done on the subject.  He points to these studies into E. coli “seasonality in humans.”

-A review of E. coli O157:H7 diarrhea in the U.S. by Slutsker et al (1997) found that E. coli O157:H7 was isolated most frequently from patients during the summer months.

-Results from an epidemiologic review of E. coli O157:H7 outbreaks in the U.S. (1982-2002) showed that outbreaks involving ground beef peaked in summer months (Rangel et al, 2005).

-In a review of non-O157 Shiga toxin-producing E. coli infections in the US from 1983-2002 revealed that these infections also were most frequent during the summer (Brooks et al, 2005).

-In Scotland, HUS and E. coli O157:H7 infections peaked in patients under 15 years of age in July/August, followed by a plateau from June to September (Douglas et al, 1997).  The prevalence in Scottish beef cattle at slaughter was found to be highest during the winter, but the concentration of E. coli O157:H7 (number of bacteria shed in cattle feces) was highest during the warmer months (Ogden et al, 2004).

Marler also found support for “seasonality in ruminants” in these findings:

-Numerous studies in cattle indicate that fecal shedding of E. coli O157:H7 is typically low in the winter, increases in the spring, peaks during the summer and tapers off in the fall (Edrington et al, 2006; Hancock et al, 2001; Hussein et al, 2005, etc.).

-Barkocy-Gallagher et al (2003) found that the prevalence of E. coli O157:H7 in cattle feces peaked in the summer, and prevalence on hides (a known risk factor for beef contamination) was highest from spring through fall.
 
-A survey of ground beef samples in the US showed that they were 3 times more likely to be contaminated with E. coli O157:H7 from June – September (Chapman, et al 2001).

-A survey in the UK found that the majority of retail meats that tested positive for E. coli O157:H7 were collected between May and September.

Among the reasons Marler thinks there are seasonal differences in the prevalence of O157:H7 in both humans and cattle are:

-Differences in handling and cooking food, or differences in consumption patterns during the summer, especially ground beef (outdoor BBQs, picnics, summer camps).
 
-Higher prevalence of E. coli O157:H7 in cattle feces and hides entering the slaughterhouse.

-More outbreaks linked to swimming pools, recreational water, and agriculture fairs during the summer.

-Speculation that temperature may affect shedding or survival in feces (warmer months promoting survival and/or growth of E. coli O157:H7).

-Studies by Edrington et al (2006 and 2008) suggested that day length and effects on hormones such as melatonin secretion from the gastrointestinal tracts might be the underlying mechanism for seasonality in cattle. The authors hypothesized that the seasonal variation is a result of physiological responses within the host animal to changing day-length. Hormones have been shown to play a role in the regulation of bacterial populations and host immunity.

This is why there is so much interest in monitoring what is actually happening on the E. coli front during the summer months.  Fewer recalls are usually going to translate into fewer outbreaks and illnesses.

This summer’s trend line is pretty positive, according to Drew Falkenstein, one of Marler’s associates.

“Compared to recent years, only two summer recalls totaling just under 40,000 pounds of product–particularly when the recalls were not known to be associated with any illnesses–is progress indeed,” Falkenstein says.