Is there a statistical bias against Salinas in the food safety numbers?
The underlying question surrounding this E. coli outbreak on spinach is whether there is a specific problem in the Salinas Valley. Known as the “Salad Bowl of the World”, Salinas is both headquarters and source for much of the product that gets hit with these types of outbreaks.
On November 4, 2005, the Center for Food Safety and Applied Nutrition of the U.S. Food and Drug Administration sent a “Letter to California Firms that Grow, Pack, Process, or Ship Fresh and Fresh-cut Lettuce”, which basically “encouraged” the California industry to work on issues such as eliminating the environmental reservoirs for E. coli 0157:H7, to follow “Good Agricultural Practices” and “Good Manufacturing Practices” and to fully implement the FDA’s 2004 Produce Safety Action Plan — all to reduce the frequency and severity of food safety outbreaks.
Why send a specific letter to California lettuce growers? Why not just establish good procedures for all lettuce growers? The justification is in the letter:
FDA is aware of 18 outbreaks of foodborne illness since 1995 caused by Escherichia coli O157:H7 for which fresh or fresh-cut lettuce was implicated as the outbreak vehicle. In one additional case, fresh-cut spinach was implicated. These 19 outbreaks account for approximately 409 reported cases of illness and two deaths. Although tracebacks to growers were not completed in all 19 outbreak investigations, completed traceback investigations of eight of the outbreaks associated with lettuce and spinach, including the most recent lettuce outbreak in Minnesota, were traced back to Salinas, California.
But the letter is odd in that it doesn’t relate the number of cases to production quantity. In other words, it doesn’t establish that California, in general, or the Salinas Valley, in particular, has had disproportionate numbers of food safety outbreaks.
In addition, the nature of food safety outbreaks is that larger producers are always more likely to get caught. Why? Well first, only a tiny percentage of those affected by an outbreak ever go to doctors. As of 1:00 PM Monday, September 25, 2006, the FDA was reporting 175 cases of illness due to E. coli 0157:H7 infection — which implies thousands, maybe tens of thousands or more were sickened in this outbreak. But healthy people generally just get sick and then get better. They don’t go to doctors.
So, on this major outbreak, with worldwide publicity, we only have 175 people who we know were affected.
If another growing area grows, say 5% of the volume of spinach grown in Salinas and had an outbreak of the exact same severity, we would only expect 8 to 9 people to be known to be sick. If the spinach was distributed in, say, the New York Metro area — so three people were sick in New York State, two in New Jersey, two in Connecticut and, say, one in Pennsylvania and one in Vermont. — the odds are the connection would never be made. The numbers are too small.
And how many of the 175 reported in the current outbreak only went to their doctors because of the national news? Perhaps normally only half that number would have gone.
And, Salinas is not only disproportionately large in total production but the companies that ship are disproportionately large with the best known brand names in the business. Meaning they are far more likely to be identified in food safety outbreaks.
Remember, the way spinach was tied to this initially was through a survey. The governmental agencies asked people to fill out a form and check off what they ate. The government noticed a statistical discrepancy between the forms filled out by a “control group” and the people coming in with the current case of E. coli 0157:H7. If you don’t have enough people who are sick to fill out the survey, you can’t do the survey and get any useful information.
There is talk that the government of California is going to try to help rebuild the reputation of the Salinas Valley. This is probably needed and a good idea for the state to protect such a valuable resource. But Salinas may be getting a bum rap. The statistics the FDA has published do not persuade me that Salinas has any more food safety outbreaks than other places. And the focus on Salinas may be giving other areas a false sense of security. If so, the FDA’s pursuit of Salinas may improve food safety statistics more than food safety.
