February 2009
A new, more accurate method of characterising selected micro-organisms helped pinpoint the cause of a recent Salmonella Typhimurium outbreak. The method was developed from ESR's CBRE, microbial and chemical forensics programme.
It was the first time it was applied to the investigation of a disease outbreak in New Zealand. The outbreak source, contaminated flour, was identified and a voluntary recall of the product by the manufacturer undertaken.
Dr Virginia Hope, Programme Manager at ESR’s science centre at the National Centre for Biosecurity and Infectious Disease, said the new method enabled investigators to identify linked cases of disease more accurately.
MLVA typing (multiple locus variable number tandem repeat analysis) enables scientists to pinpoint the exact strain of bacteria causing a disease.
“This meant the epidemiological investigations, which identify what infected people have in common, was more accurate as we were able to exclude people who did not have the exact same type of Salmonella Typhimurium Phage Type 42.
“Our new technique has a number of other 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,” she said.
Late last year ESR, through its national disease surveillance system, identified an outbreak of Salmonella Typhimurium PT 42 among people from several different regions.
On behalf of the NZFSA and the Ministry of Health ESR undertook a detailed outbreak investigation in collaboration with public health units.
This involved the public health units collecting detailed information and environmental samples that could be relevant to a case. ESR collated the ‘epidemiological’ data and case information and undertook detailed laboratory analysis of samples and organisms.
Analysis and cross matching of all this information led to the identification of the contaminated flour as the source of the outbreak.
- At mid January there were 65 reported cases linked to the specific outbreak. Epidemiological analysis and microbiological investigation has confirmed exposure to contaminated flour as the cause of the illness.
- ESR’s CBRE (microbial and chemical forensics programme) was developed using Crown Research Capability Funding from the Ministry of Research, Science and Technology.