- PDF Version (1.0M) - Print Friendly - Help

Food Focus June 2009

FBI under surveillance

A day off work with a squiffy tummy which we blame on a dodgy dinner is a commonplace experience for thousands of New Zealanders. It’s a scenario that is thought to cost the country around $86 million a year, mostly in lost productivity due to time off work. It’s also a cost that NZFSA is working to reduce.

New Zealand Food Safety Authority (NZFSA) public health principal advisor Donald Campbell says having accurate, detailed data is vital in developing public health policies that improve food safety and reduce the cost to society of foodborne illness. Counting the numbers is called ‘FBI (foodborne illness) surveillance’.

“It’s important not just to count the numbers – it’s got to translate into public health action, and that’s what we’re doing with our three public health strategies for Campylobacter, Salmonella and Listeria,” Donald says.

FBI surveillance is an important first step in making sensible decisions about where to focus energy and resources. To get data, NZFSA relies on the national communicable disease notification system (EpiSurv) run by Crown research institute, the Institute of Environmental Science and Research (ESR), under contract to the Ministry of Health. Doctors and laboratories are required by law to notify public health units of patients with anything on the list of 54 notifiable diseases. NZFSA’s interest is food safety, so it has ESR extract annual data for potentially foodborne illnesses, especially those traced back to infected food or linked to a food source.

Acute gastroenteritis illness is a general term for stomach upsets which may or may not be traced to a specific bug. Common foodborne bugs (which include bacteria, protozoa or viruses) are Campylobacter, Salmonella, Listeria, Escherichia coli (E.coli), and norovirus. Campylobacter etc is the name of the pathogen that makes you sick, while campylobacteriosis is the name of the disease the bug causes.

The tip of the iceberg

The actual numbers notified are just the tip of the iceberg, says Donald.

“It’s very difficult to get accurate information about the causes of many acute gastro illnesses – especially which of them are from food, as opposed to contact with infected animals, water, or people. We rely on data that has been officially notified by doctors or laboratories and then where the type of illness has been confirmed by laboratory tests.

“The reality is, many people don’t go to the doctor in the first place, or if they do go they don’t have lab tests done, or they might have tests which then fail to identify the pathogen that’s caused the illness. There is fallout all the way through the system and this affects the accuracy of the information we get.”

This pattern is called the ‘notification pyramid’.

“We don’t know the number of cases of foodborne illness that go either unrecognised or unreported, but we do know that it is much greater than we see in actual numbers notified,” Donald says.

Estimates of the true impact of foodborne illness on human health and costs to the community are based on two kinds of studies. The first are localised studies undertaken by choosing a random sample of general practices, then taking stool samples from every person with diarrhoea who walks in the door to screen for the kinds of bugs that cause acute gastro illnesses. It’s very expensive, with one such study in Britain costing £5m.

In New Zealand, we’ve approached it by doing a community survey, Donald says. Over a year, about 300 people a month are surveyed randomly by phone. They are asked if they have had diarrhoea or vomiting or other symptoms of acute gastro illness, and time off work as a result.

“The trouble with that approach is that you can only say they’ve had acute gastro-intestinal illness, but you don’t know what type they’ve had. But it helps build a picture of the cost to the community in terms of work days lost due to acute gastro-intestinal illnesses.”

NZFSA then uses the British or USA localised studies to estimate how many of those illnesses are from food sources.

“We can use the UK and US figures and extrapolate information for the New Zealand situation using different multipliers for different diseases. We know for example that almost 100% - or 1 in 1 of listeriosis cases get notified because almost everyone who gets ill from Listeria seeks medical help and ends up in the system. But for Salmonella it’s about 1 in 3 and for Campylobacter is more like 1 in 8.”

Shaping public health goals

So, counting the numbers gives good baseline information and allows for ongoing monitoring and evaluation of programmes. But what about the all-important action? Information from the foodborne illness surveillance data was used to select NZFSA’s three strategic public health goals: reducing campylobacteriosis by 50% and salmonellosis by 30% over five years, and seeing no increase in the incidence of foodborne listeriosis despite an increasing range of higher risk foods becoming available.

“We chose these diseases because two are the most commonly notified (campylobacteriosis and salmonellosis) and listeriosis is one of the most severe,” Donald says.

Campylobacteriosis and listeriosis between them create the highest human health burden in New Zealand. In 2007 more than 12,776 cases of campylobacteriosis were reported with the majority of them attributed to food. Listeria had just 26 cases notified, but 20 were attributed to food, and the potential effects of listeria are the most severe as it can cause abortion or stillborn births in pregnant women and death in other vulnerable groups.

Salmonellosis came a distant second in the numbers game, with just 1,274 notifications – around 60% of those due to food. The choice of salmonellosis as a public health goal also allows us to see how New Zealand’s monitoring programme stacks up against those in the United States and United Kingdom, providing international comparisons on the effectiveness of our food safety strategies.

In developed countries, effective surveillance of foodborne illness is fundamental to food safety systems. Because of this, the World Health Organization is developing a global approach to improve foodborne disease surveillance. New Zealand is part of that initiative.

“It is useful to be part of the global network for foodborne illness surveillance because it allows us to share approaches and to compare and validate the results. It allows us to get more bang for our buck,” Donald says.