Effect Measure

The Wall Street Journal (WSJ) calls it a “reality check,” meaning, in their terms, a check against the mistaken idea that there is more foodborne illness these days. That’s one way to look at it. Another is a look that is reality based. The reality is that there is a tremendous health burden from tainted food that is unaddressed, at least going by the same CDC Morbidity and Mortality (MMWR) report the WSJ was citing. MMWR was reporting on 2008 data from FoodNet on the incidence of infection from enteric pathogens commonly transmitted via food:

Despite numerous activities aimed at preventing foodborne human infections, including the initiation of new control measures after the identification of new vehicles of transmission (e.g., peanut butter–containing products), progress toward the national health objectives has plateaued, suggesting that fundamental problems with bacterial and parasitic contamination are not being resolved. Although significant declines in the incidence of certain pathogens have occurred since establishment of FoodNet, these all occurred before 2004. Of the four pathogens with current Healthy People 2010 targets, Salmonella, with an incidence rate of 16.2 cases per 100,000 in 2008, is farthest from its target for 2010 (6.8). The lack of recent progress toward the national health objective targets and the occurrence of large multistate outbreaks point to gaps in the current food safety system and the need to continue to develop and evaluate food safety practices as food moves from the farm to the table. (Morbidity and Mortality Weekly Reports, CDC)

FoodNet is an active surveillance system using disease diagnosis laboratories in 10 states. “Active surveillance” means CDC actively queries the laboratories on a regular basis rather than waiting passively for voluntary reporting. Moreover the system is “population-based,” meaning that it is designed to collect all laboratory confirmed cases from selected pathogens from a defined population base. This allows calculation of rates of new cases appearing in the 10 states, an estimate of risk. The enteric pathogens currently in the FoodNet system are Campylobacter, Listeria, Salmonella, STEC (shiga-toxin producing E. coli, the “Jack-in-the-Box outbreak” E. coli) O157, Shigella, Vibrio, and Yersinia (since 1996), Cryptosporidium and Cyclospora (since 1997), and STEC non-O157 (since 2000). Since 2004 FoodNet has also been relating the infections to reported outbreaks. While only covering 15% of the US population (those in California, Colorado, Connecticut, Georgia, Maryland, Minnesota, New Mexico, New York, Oregon, Tennessee), the system provides important information not otherwise available. And the reality it allows us to glimpse is not very comforting.

The infection with the highest incidence rate in the surveilled population was Salmonella, with 16.2 new cases per 100,000 population in 2008. That’s an average for all 10 states, but there is significant variation between states. New Mexico had the highest (26.40 cases/100,000 population), New York the lowest (10.15). For a more average state, like Tennessee, whose incidence rate was 14.63/100,000 population (Table 1 in the MMWR report), it means is that if you live in a city like Memphis, Tennessee, with a population of about 650,000, you might expect 6.50 times 14.63, or about 95 cases of Salmonella in 2008. Overall, the most affected age group for most agents was children under the age of 4. This may be an artifact of more active diagnosis in children compared to adults. The risk of ending up in the hospital, however, was greatest for people over the age of 50. Most (75%) of the reported infections were not part of recognized outbreaks. Two big Salmonella outbreaks (the produce and peanut butter multi-state events) were captured in the FoodNet data.

Food safety experts know the laboratory confirmed cases provide a gross underestimate, however. Most people with foodborne salmonella infection aren’t diagnosed by any doctor or clinical laboratory. The rule of thumb is that for every diagnosed case there are probably 10 unrecognized ones, so that would mean about 1000 salmonella cases in Memphis last year. Assuming this is an avoidable illness (and it is), this is a pretty expensive bill to pay in terms of lost work days, productivity, cost for medical care or over the counter meds, not to mention pain and discomfort. If part of a recognized outbreak, there is also the econommic losses of the restaurant or recalled food items to consider (the salmonella peanut product contamination is estimated to have costs in the billions of dollars). And while it is the most common laboratory confirmed foodborne illness, some of the other less common ones can be much more serious and hence much more costly.

While valuable, the data remain limited. As the authors point out, changes in laboratory diagnostic practices (like increased use of non-culture testing) may distort trends and estimates for specific pathogens. Moreover some common agents, principally viruses like norovirus, are not routinely tested for in these laboratories. We also know that different demographic groups (like people of different races or ages) have different care seeking behaviors, which means that the likelihood of diagnosis will differ along with risk in these different groups. Finally, we are dealing with a 15% possibly non-representative sample of the US population.

In fairness to the WSJ they also state that the report observes there are ?gaps in the current food safety system,” although only at the end of a short squib whose lede is the notion that there is no recent increase, an uncertain and minor element in the MMWR report. The overall impression given by the WSJ piece is that the current situation is nothing special to worry about (because it’s not much different than previous years). That’s like saying that illiteracy or crime are nothing to worry about because they’re not much different than previous years. The real lede should have been this one, from the report itself:

The lack of recent progress points to gaps in the current food safety system and the need to continue to develop and evaluate food safety practices as food moves from the farm to the table.

Comments

  1. #1 sondaze wybory demokracja
    April 15, 2009

    It really scares me that nowadays we are endangered with what we eat.
    I don’t meant socalled junk food but almost all victual within our reach. Pathogenic factors are literally everywhere – on (sometimes in as well) fruit and vegetables, in eggs, not to mention meat… Technology that was believed to protect us turned out to be harmful product of humankind.
    We try to fight with ‘bio’ and ‘organic’ food, but isn’t it just a comeback to what our ancestors ate? It’s funny that with our whole development we need to learn a lot from them.
    But better late than never. The first step is already done – we are becoming more and more aware, that we are what we eat.

  2. #2 ebohlman
    April 15, 2009

    It seems to me that there are two completely separate questions here:

    1) How does the incidence of food-borne illness compare to the past?

    2) What level of harm results from the current incidence of food-borne illness?

    It’s certainly possible that the incidence is down, yet the level of harm is still unacceptable. There’s no contradiction there. In fact it’s even possible that while the incidence has decreased, the level of harm has increased (analogy: while illiteracy has greatly declined, it’s become more of a problem because it’s much harder for illiterate people to get by now than in the past).

  3. #3 revere
    April 16, 2009

    ebohlman: You are right that these are two separate question, which is why I was a bit taken aback by the emphasis in the WSJ. In this case, incidence isn’t down. It just isn’t obviously up.

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