Hygiene Alert

A sea change is taking place in the way public health professionals are combating the threat posed by two of the most significant foodborne pathogens. Surveillance and testing and improvements in food hygiene and safety practices on their own can no longer be relied on to reduce the incidence of food poisoning.

Public health experts are noticing disturbing new patterns of disease that are targeting the over-60s, which may be linked to food hygiene in the home.

Anecdotal evidence suggests the types of food they are buying, how they are storing it and preparing it and their consumption patterns could explain the sudden spike in listeria and, more recently, campylobacter.

Now the Health Protection Agency (HPA) and the Food Standards Authority (FSA) are combining their areas of expertise to investigate the causes.

Cases double

In 2004/5 HPA surveillance experts noticed a marked change in the epidemiology of human Listeria monocytogenes infection in the UK. The incidence of listeriosis among the over-60s had doubled since 2001.

“Listeria is more or less ubiquitous. Most people will come across it but not get an infection or one that gives rise to disease,” says Dr Bob Adak from the HPA’s Centre for Infections, who is briefing the FSA’s Advisory Committee on the Microbiological Safety of Food (ACMSF).

“For certain groups, mainly pregnant women and the elderly, it can give rise to severe illness. So there must be some sort of host factors that determine whether such people, when exposed to the same levels of listeria as others, then manifest illness.”

Public health experts are baffled as to why the elderly suffer most from the disease. During the 1990s the number of cases of listeriosis among pregnant women rose sharply and the FSA advised against eating risky foods such as paté or unpasteurised cheese.

Surprisingly, HPA data shows that the incidence of listeria among traditionally vulnerable groups such as pregnant women and newborn babies has remained relatively constant since 2001. This suggests that the spike in listeria among the over-60s is the result of other, unexplained, factors.

High mortality

According to Dr Adak there are fewer than 200 cases a year. But listeriosis has a high mortality rate. With one third of sufferers dying, it claims more lives each year than salmonella and E. coli 0157 combined.

Until March, the rise in cases of listeria was distinct from trends in other gastrointestinal diseases, where numbers were stable or declining. But now a similar pattern is emerging with campylobacter, where the over-60s are at greatest risk of infection. 

Campylobacter is rarely fatal – 45 deaths were recorded between 1993-2006 – but it is unpleasant and about 10 per cent of laboratory confirmed cases require hospital treatment. The number of cases has been increasing since 2005 and between 1990 and 2007 cases among the over-60s trebled.

Dr Iain Gillespie from the HPA Centre for Infections suggests the rise in campylobacter is unlikely to be explained by improved case recognition, as the age distribution of cases of laboratory-reported salmonellosis or cryptosporidiosis has not changed to the same extent.

The unexpected rise of listeria and campylobacter among the over-6os has prompted the FSA to explore wider behavioural factors, such as shopping habits, storage and preparation of food in the home and consumption patterns.

“If you look at the kind of products where listeria is an issue, it’s going to be ready-to-eat foods,” says Jenny Morris, CIEH’s food policy expert. “The particular issues you’ve got are about temperature control and date labelling and how people use their fridges.

“When you bring campylobacter into the mix, some of the risk factors are different because that’s about raw food. It involves proper cooking and avoiding cross-contamination.”

The FSA believes that one reason for the listeria increase is that people are not following the use-by dates on chilled ready-to-eat foods, such as pre-packed sandwiches, salads, cooked sliced meats, smoked salmon, soft cheeses and patés.

“There are some indications that problems in this age group could be linked to eating cold meats past their use-by date,” says Ms Morris.

“One hypothesis that needs testing is that larger packs are purchased, as they are better value for money. If consumption rate is low, then shelf life may be exceeded, increasing the food safety risks.”

If elderly people are ignoring the use-by date, this may not be the result of ignorance. Many of the body’s functions become impaired with age and problems with vision are common, making it difficult to read expiry dates and preparation instructions.

Hygiene alert

To reverse this trend, the FSA is promoting food hygiene advice for the over-60s in its annual Food Safety Week, which runs this month.

Catherine Clarke, FSA senior marketing manager, says the main focus is on listeria but the agency also plans to promote a broader message by highlighting the importance of the four Cs – cooking, cleaning, chilling and cross-contamination – to help reduce foodborne disease.

From 15-21 June, it will attempt to raise awareness of the dangers of listeria in the home by using GP surgeries and pharmacies in areas with a high proportion of over-60s. It is producing leaflets and posters and handing out fridge thermometers to encourage people to think about their behaviour.

Local authorities that participate in Food Safety Week are also being encouraged to promote this information.

“We are looking at some of the behaviours that can help to reduce the risk of listeria growing such as using food by its use-by date, making sure things are stored properly, reading the instructions on the label and also keeping the fridge at the correct temperature between 0°C and 5°C,” says Ms Clarke.

The focus on behaviour in the home came about after the ACMSF set up a study of vulnerable groups in June 2007, which identified four hypotheses to explain the increased incidence.

The first query was whether the rise in cases of listeriosis in people over 60 was the result of improved case recognition. Were clinicians now detecting infections previously missed because patient management and/or laboratory testing protocols for the diagnosis had changed?

The study also explored whether the over-60s had become more susceptible to Listeria monocytogenes as a side-effect of changes in treatments for common conditions.

Dr Gillespie says there is a possible link. “We are surviving for longer with chronic conditions and some of the treatments increase our susceptibility to infectious disease, including food poisoning organisms.”

The third hypothesis examined whether the strains of Listeria monocytogenes responsible for the recent rise in cases in the over-60s were more virulent than those in the past.

Finally, the study examined whether the levels of listeria exposure had increased as a result of food contamination, changes in the processing and composition of foods, or changing patterns of consumption, or food storage at home.

The study was able to eliminate the first hypothesis as a factor in the increase in listeriosis cases.

The second hypothesis indicated other factors were mainly responsible for the rise among the over-60s and raised queries about vulnerabilities and susceptibilities that need further research.

“As we live longer, we will be on more drugs to control blood pressure, diabetes, malignancies, so by the time you are in your sixties you might, on a daily basis, be having four or five different tablets,” says Dr Adak. “How they interact and what it means in terms of your susceptibility to disease is something that I think needs to be looked at.”

One group of drugs identified is proton pump inhibitors, whose main action is a pronounced and long-lasting reduction of gastric acid production. This is a concern because stomach acid levels can act as a natural defence against listeria multiplying in the gut.

Food changes

In the case of the third hypothesis, the group concluded that changes in the food chain, including food preservation technologies, may have allowed an increased infection among the over-60s but there was no definitive evidence to support this.

Increasingly, the finger appeared to point to the final hypothesis. “That’s the interesting one because one of the things that showed was that we really don’t know an awful lot about what people do in the home with food,” says Ms Morris.

“We don’t really know a great deal about practices generally or within this age group. There are a number of assumptions made but the supporting evidence is sparse.”

The study group’s draft report for the ACMSF acknowledges that data on food shopping and behaviour and consumption patterns among the over-60s is limited and calls for more information to inform them about the factors contributing to the risk of listeriosis.

“Elderly people might have certain patterns of consumption, which are different,” says Dr Adak. “It could be that people are buying food less frequently and keeping it longer.

“You are more frugal. Your income has declined and, particularly in times like this when those members of the population who may be dependent on their savings have seen the interest rates cut, they might have less money to spare. So their food buying habits and how they look after their food might change.”

People who have been widowed may be particularly vulnerable. When there is only one person to cook for, there may be a temptation to take the easier option of ready-to-eat foods.

The importance of social research into behaviour in the home is vital to complement surveillance, as it is hard to collect sound data on food habits from older people with listeriosis.

“We aim to capture data on all cases of listeria to try to determine what might have caused their illness. The problem is approximately 50 per cent of the cases in the older age groups die because it is a severe infection and they are often very ill with other conditions,” says Dr Gillespie.

“When it comes to food eaten, we only choose the last 30 days because this generally covers the time from exposure to illness for listeriosis. It is a good cut-off point for people when they try to recall what they have eaten. Even then, there is always a possibility that there will be things that they have forgotten or alternatives that they report.”

Progress is being made. After the publication of the draft report on listeriosis in March, the ACMSF asked the FSA’s social science research committee to advise how it could help explain the rise.

A working group has been formed to provide an interim advice paper, which will be presented to the next ACMSF meeting in September.

Brad Smythe at the FSA says its objectives will include commissioning research to find out what foods elderly households consume, how they store them and how they prepare them.

Dr Adak believes the research will be valuable in a range of areas. “If we are looking at ‘can elderly people read labels because the writing is so small?’ the result applies to a whole range of other things that will benefit them in terms of avoidance.

“Are you reading the cooking instructions properly? Are you microwaving your food for the correct time? There will be wider spin-offs from doing things like this, which don’t just apply to listeriosis but might apply to diet and other things as well.”

Early reports suggest the focus of the social science research will be on the domestic setting, although the working group is being encouraged to include carers’ awareness of older people’s behaviour and their own behaviours, which could present risks.

Other research will also be commissioned to look at those aged over 60 who have weakened immune systems as a result of illness/medication to reflect the fact that the majority of cases have an underlying condition.

International dimension

There may also be an international dimension to some of the research. Cases are rising in other European countries and similar changes have been reported in Germany, Belgium, Denmark, France and Lithuania.

In a novel move, Dr Adak’s team at the HPA has been asked to collaborate with the social scientists to investigate the increase in incidence of listeria.

He is excited about the new working arrangement. “We have to engage with a wider range of specialists to do the work because it’s not as straightforward as it was in the past. The organisms change and evolve.

“We’re now at the stage where in terms of public health, you have to deal with clinicians, social scientists, environmental health specialists and a whole panoply of people working together to bring expertise from all these areas and looking at these things far more closely than we did.”