The agency said there have been no further confirmed cases since the first week of October and noted a peak in September. 38 people had been hospitalised, according to an earlier update.
MPI released case-control studies, commissioned by the Ministry of Health, which provided direction for investigation but did not identify any affected or contamination food or its source.
Not a simple situation
Scott Gallacher, MPI deputy director general regulation and assurance, said health data points to a contamination in August, which was identified as an outbreak of illness on 23 September.
“We are getting a lot of information, building a picture and investigating many avenues,” he said.
“It is not a simple situation where we can recall a single product. It is not definitively linked to any one producer, distributor, wholesaler or retailer.”
Gallacher said the case-control studies from Environmental Science and Research’s (ESR) identify a range of foods that need further investigation to establish if they are the source of this illness.
“In the case of lettuce, which is identified as a food to investigate, there are numerous varieties of whole lettuce, leaves, leaves of mixed varieties, and premixed salads, covered by many brands,” he said.
“Lettuce is a very commonly consumed food, which was consumed throughout this outbreak with the vast majority of consumers not becoming ill.
“Most of the patients surveyed remembered eating some kind of lettuce, with 8 out of 96 remembering one brand, but the vast majority of those surveyed could not specify the type or brand of product.”
Confidence in standards
Dr Hans Maurer, United Fresh knowledge officer, said it is providing advice and support to 84 members as authorities work to identify the source of this illness.
The national pan-produce industry organisation said it was confident that systems and processes used by its members meet standards which are being checked by MPI.
“We are also working closely with MPI to understand the level of risk associated with the spread of the bug. It is our understanding the source may never be confirmed.
“It is important to note the MPI’s investigation is over a range of foods, and not isolated to fresh fruit and vegetables and the early speculation has been somewhat unhelpful.
“The ESR report…unfortunately does little to assist in authoritatively pinpointing the source of the outbreak, and one has to question the effectiveness of an after the event logistic regression model approach to providing meaningful answers to the valid food safety related questions that have arisen.”
MPI criticised
Damien O’Connor, Labour’s food safety spokesperson, criticised the decision not to release the information from ESR when it was first received.
“When it comes to food safety, MPI surely knows it is always better to be safe rather than sorry, yet it has been anything but helpful to consumers since the outbreak was confirmed last month, leaving it up to a concerned medical specialist to warn the public about potential sources.
“Given the investigation is ongoing, it is now up to MPI to relay any further material it receives from ESR to consumers so they can make informed decisions about their food purchasing choices.
“MPI’s handling of this reinforces concerns about resourcing at the Ministry and adds fuel to Labour’s repeated calls for an independent food safety agency.”