An outbreak of Salmonella typhimurium (one of the many bacteria that can cause food poisoning) in 2009 was quickly identified and contained and the source of infection located thanks to techniques developed by ESR (Environmental and Scientific Research) scientists.

Noticing the outbreak

At the end of 2009, more people than usual had gone to their local doctor or hospital complaining of gastroenteritis. Several doctors decided the illness needed further investigation, and collected poo samples from their patients. These were sent off for further testing. The testing laboratory grew bacteria from the poo samples on an agar plate and identified the bacteria as Salmonella. The bacteria sample was then sent on to ESR to determine the exact strain of Salmonella involved.

Tracking the outbreak

A new technique called MLVA typing (multiple locus variable number tandem repeat analysis) enabled the scientists to work out the exact strain of Salmonella causing the outbreak. This meant that related cases could be linked and people who had other types of Salmonella poisoning could be ruled out.

The type of bacteria was identified as Salmonella typhimurium phage type 42. The scientists then carried out epidemiological investigations to identify what the infected people had in common.

As at mid-January 2009, there were 65 identified cases of this particular strain of the disease. Curiously, the infected people were from several different regions of New Zealand. It turned out that the people who were sick had all been baking and had eaten some of the raw product (for example, they had licked the spoon they were cooking with) or they had been playing with home-made playdough. The bacteria was traced to contaminated flour. It’s likely that the flour was from the same batch, but several different companies had packaged the flour for selling in shops and supermarkets. The companies all issued recall notices for the flour through radio, television and newspapers.

Dr Virginia Hope, Programme Manager at ESR’s science centre at the National Centre for Biosecurity and Infectious Disease, said the new MLVA typing technique has a number of advantages over the methods previously used to analyse microbiological samples. “It produces much faster results, a larger number of samples can be processed simultaneously and the data is easy to compare.”

Find out more about food poisoning and being a food detective.

Useful link

ESR (the Institute of Environmental Science and Research) is New Zealand’s Crown Research Institute that specialises in science relating to people and communities.


    Published 6 April 2009