KEY POINTS:
Health authorities are investigating an outbreak of salmonella which is implicated in the death of an elderly woman.
Food that was distributed around the country is thought to be the cause - but scientists testing leftovers from people's fridges have not yet found infected samples.
Nationally, health boards have reported 28 cases of people being infected with the mbandaka strain of salmonella, which is rarely seen in New Zealand.
Ten of the cases occurred in Nelson-Marlborough, where a woman who had been infected with the strain died in February in Nelson Hospital.
Other areas affected include Auckland (one case), Waikato, Wellington, Christchurch and Dunedin.
Salmonella infection typically causes diarrhoea, stomach cramps, fever, nausea, vomiting and headache. The elderly and the very young are at increased risk of complications, such as dehydration.
This year to mid-March, 259 cases of salmonella - there are many strains - were reported nationally, compared with 307 in the first three months of last year.
The Ministry of Health's director of public health, Dr Mark Jacobs, said last night that in 15 cases of the outbreak the mbandaka strain involved had been genetically typed. In 14 cases they were identical and the other was "96 per cent the same".
"It's a very strong indication, if we find there's numbers of cases of a particular species, if they are identical genetically, it means it's part of the same outbreak. In all likelihood we are talking about a food."
This theory was strengthened by the fact there had been relatively little recent travel by the 28: one had been overseas, one had been in contact with someone who had, and some had travelled within New Zealand.
