Thursday, May 26, 2011

Sarah Carter - confusion reigns

On 12th March, 2011, I wrote about the tragic death in Chiang Mai of Sarah Carter.

Originally, her death was blamed on consumption of toxic seaweed.  At the time, I suggested that this was a highly suspect conclusion, based on the symptoms and the circumstances.

A short while later, it was claimed that Sarah and her two friends had been infected by an ECHO virus.  The symptoms matched.

However, more information came to light - a Thai tourist guide had died in the next room in the same hotel and a week earlier, two other tourists had died in a room one floor below. 

The New Zealand TV3 channel discovered that a total of seven tourists had died in Chiang Mai in similar circumstances.  Sara Hill, an investigative reporter for TV3, went to Chiang Mai and made a programme screened here a couple of weeks ago.

In an interview with Sarah Carter's friend, Sara Hill discovered that none of the three girls had eaten seaweed and had eaten two different meals.  They all developed sore stomachs and vomiting and were hospitalised.  According to a Thai cardiologist, Sara Carter suffered very low blood pressure, dehydration and low blood flow to the kidneys, with ultimate kidney failure.

The reporter managed to obtain swab samples from the room occupied by Sarah and returned them to New Zealand for testing.  Traces of chlorpyrifos, an organo-phosphorus insecticide used in corn and cotton farming, were found in the swabs.  Dow Chemical Company voluntarily withdrew the registration of chlorpyriphos for domestic use in 2001.  Mr. Ron McDowell, a UN scientist, hypothesised that Sarah had been exposed to chlorpyrifos as a result of over-zealous spraying of the hotel room to control bed bugs by a pest control operator.  McDowell claimed that the symptoms and pathology all fitted with chlorpyrifos poisoning.

However, the swabs were taken three months after the room was occupied by Sarah, so spraying could have occurred at any time during those three months. The report form was shown in the programme.  The level in Sarah's room was given as <0.1 microgram/sample, which probably means "below the limit of detection".  A sample from an air conditioner was 0.24 micrograms/sample, but the film of the sample being taken suggested that the area swabbed was uncontrolled.

The half life of chlorpyrifos in the human body is about one day, so, although it is absorbed quickly, it also disappears from the body quickly.  Thus tests at the hospital may not have shown its presence in Sarah's body.

I'm not convinced that we are much further forward.  The Thai authorities were not being particularly cooperative with the TV3 investigation and recently refuted the chlorpyrifos theory.  Three toxicologists in New Zealand have issued a statement criticising the programme and the conclusions drawn by the experts consulted by Sarah Hill.

It looks as though seaweed is off the hook and food poisoning seems a bit unlikely, as the three girls ate different meals, but suffered similar symptoms not commonly seen in microbial food poisoning.  Food contamination is not completely ruled out, as several meals could have been contaminated with a chemical.

I don't know if we will ever know the true story

Friday, May 13, 2011

Kiwifruit dumped

It's been a mixed year for New Zealand kiwifruit growers.  Earlier in the season, some vines were found to have been infected by Pseudomonas syringae pv actinidiae (Psa) - a bacterial disease first identified in Japan about 25 years ago.  The Asian strain causes leaf spotting and some die-back of vines, though it is far less savage than the Italian strain that has also been found in one area.

In the last week, 100,000 trays of kiwifruit have been withdrawn from the market (some had already been shipped and will be intercepted) and will be destroyed.  It appears that a worker on a harvesting gang has been diagnosed with typhoid, picked up overseas before arrival in New Zealand.  Since it is not possible to isolate the specific fruit handled by the worker, all the fruit picked by that gang has been withdrawn.

The risk of infection being carried on the fruit is very low, but Zespri, the main marketer of New Zealand's $1.5 billion kiwifruit export industry, has been cautious and manned up, taking the pro-active response to prevent any possible disease risk for consumers.  This action is in stark contrast to those of some overseas companies that have attempted to conceal the potential of their products to cause harm to consumers.

The value of the withdrawn fruit is around $800,000 and represents less than 0.1% of this year's expected kiwifruit exports.  However, the unfortunate growers may not be insured, so this will be a serious loss to some orchardists.

Tyhpoid is caused by Salmonella enterica enterica, serovar Typhi, a bacterium that infects the intestine, resulting in damage to the intestine and fever.  Resultant diarrhoea can lead to transmission of the bacteria to other people and the environment.

The disease was named from the spike in infections observed after severe typhoons.  The contaminated water and poor sanitary conditions that followed the typhoons provided the conditions for increased numbers of infections.

  Mary Mallon was an itinerant cook, having arrived in America around 1874 from Ireland.  She became a domestic servant and eventually a cook in New York.  Though she appeared healthy, between 1900 and 1907, Mary had seven cooking jobs where 22 people  became ill and one died of typhoid.  After an investigation, Mary was taken by force and held against her will without trial.  This occurred at a time when the symptomless carrier state was unknown, so the investigation was quite innovative.  Mary was effectively imprisoned under sections 1169 and 1170 of the Greater New York Charter and lived alone in a cottage on North Brother island.

After her release, Mary eventually went back to cooking and this time was sent to the island for a period of 23 years, which ended only when she had a stroke.  She died six years later.

Mary was then and is still known as Typhoid Mary.

If you want to read more about Mary Mallon, go to Jennifer Rosenberg's 20th Century History page:

Sunday, May 8, 2011

Hazard or Risk?

The words "Hazard" and "Risk" are often used rather loosely in everyday speech. e.g.  "Cycling to work in Auckland is a risk". What does this mean?

I read an article today that attempted to clarify the situation.  Unfortunately, the writer got it wrong and increased the possible confusion.

In terms of food safety, a hazard is something that has the potential to harm the health of the consumer, such as the presence of a piece of glass in a cheesecake.  Hazards may be biological, chemical or physical.

The risk is the probability of the hazard occurring.

The other thing we need to consider is the severity of the outcome.

Let's take a non-food example to show the importance of understanding these terms.

The hazard under consideration is getting hit by a wheel falling from an airliner.

We know that the risk (probability) of this happening is very low.

But if the event does occur, the severity of getting hit by falling debris is very high, possibly lethal.

Now think about hazard, risk and severity in the food safety context.