December 12, 2016

Why no chicken enquiry?

There’s an inquiry into the water contamination in Havelock North. However,  Otago’s Michael Baker points out there are about that many cases of disease caused by Campylobacter in chicken every two months. He asks “So why aren’t we having a national enquiry about that problem?”

Prof Baker was presumably intending this as a rhetorical question, but thinking of it as a serious question is a good illustration of risk perception.  It’s pretty clear that we do (as a society) care more about Havelock North’s water supply than about chicken contamination. Why?

  • Control.  Most people would think (largely correctly, not that it matters for the perception) that they could protect themselves from Campylobacter in chicken by taking reasonable care in preparing it. There aren’t any simple, everyday measures to protect yourself from your water supply.
  • Purity. We’re trained to think of raw chicken as dirty, but to think of NZ aquifer water as clean and uncontaminated — to the extent that people aren’t willing to even consider chlorination of some of these water supplies.  The Havelock North incident was a desecration.
  • Salience (reporting): The Havelock North cases happened all in one place, over about the ideal length of time for a news story — long enough for reporters to get there and interview people, and have news every day, but not long enough for it to get boring. It was all over the news. The media don’t report the sporadic cases. Stuff has a story today about Consumer NZ testing raw chicken, but the last reports I could find there of individual cases were smaller outbreaks due to raw milk contamination in 2014 and liver contamination in 2012. The most recent individually-described case report I could find from food that wasn’t a specific contamination incident was in 2009.
  • Salience (topic): Water pollution is becoming an increasingly important environmental issue in New Zealand, and even though nitrate and phosphate in streams is a different problem from Campylobacter in tap water, they feel connected through intensive agriculture (the inquiry should tell us something about this, not that it matters for the perception).

A more difficult question is whether the higher concern about Havelock North is evidence that we’re not thinking about this right, or evidence that comparing the case numbers isn’t the right way to think about it.

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Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »

Comments

  • avatar
    Megan Pledger

    Possibly also governance – the media holds the government to a higher standard of protection than it does of private industry. Possibly because the media is a private industry but also because it resonates with readers.

    7 years ago

  • avatar
    Beatrix Jones

    An outbreak is scarier because it has the potential to overwhelm the health system (although it sounds like they did OK in Havelock North). They did close schools, which wouldn’t happen with sporadic cases. So because of the outbreak (rather than sporadic) nature, even people who didn’t get sick were affected.

    7 years ago