Beware of lemon meringue pie

Microbe of the month: Bernard Dixon on the return of salmonella

With summer around the corner, a warning to campers. Life under canvas can provide the perfect conditions for bacteria to proliferate in foodstuffs, according to a new report of a gastroenteritis outbreak caused by Salmonella enteritidis during a camping holiday in north Wales. Thirty-three people were admitted to hospital with diarrhoea, vomiting and abdominal pain.

Describing the incident in Epidemiology and Infection, Ruairi Brugha of the Central Public Health Laboratory in Colindale, with colleagues in Cardiff and Bangor, points out that infected eggs pose a particular danger to campers. The victims in the Wales case - the first reported outbreak caused by a new type of S. enteritidis discovered in 1993 - were on a trip organised by a Boys and Girls Brigade group. The 12 adults and 37 children (aged nine to 17) brought tents, ovens, cooked and uncooked food from their home town 300 miles away. But they had no refrigeration facilities. Three days after they arrived, 46 of the 49 members of the party went down with gastroenteritis. The condition of 33 of them soon deteriorated, and ambulances ferried the victims to hospital. Thirty-one of them had to be intravenously rehydrated.

The bacteriologists who investigated the incident found the campers had discarded the remains of the meal consumed the evening before the first symptoms appeared. Though they could not test the foods, the investigators screened samples of faeces from all the campers for disease-causing bacteria.

A comparison of these results with the food items eaten by individual campers quickly highlighted lemon meringue pie as the most likely - indeed the only - source of infection. Every one of the 42 individuals who had eaten the pie had become ill. And every one of them had S. enteritidis in their faeces, except one who had eaten only three or four spoonfuls. None of the faecal samples contained any other hazardous microbes.

The pie had been made from eggs, pastry, sugar and lemon powder. The eggs came from a batch laid 13 days before theoutbreak, transported from the campers' home town and stored at the camp in warm summer temperatures for two days before the pie was made. Two cooks produced the pie mixture, containing 20 egg yolks, boiled it for one or two minutes and then left it at ambient temperature for four hours. They added a meringue topping, made with egg white that had also been standing for four hours, and put portions of pie into three ovens at gas mark 6 for five to 10 minutes to brown. The pie then stood at ambient temperature for another 2-3 hours before being eaten.

Tests on the remaining six eggs failed to show S. enteritidis, so the investigators could not pinpoint the source of the outbreak with 100 per cent certainty. However, the dangers posed by this bacterium in eggs and egg products have become clear over the past decade (though Edwina Currie exaggerated the risk in 1988). Together with other evidence, this makes the origin of the Welsh incident virtually certain.

Given that the bacterium can occur in eggs, the ways of preventing it from causing illness are to reduce its chances of growing (by refrigeration) and to kill it (by thorough cooking). On this occasion, S. enteritidis had ample opportunity to multiply while the eggs, pie mixture and pie were left at ambient temperature and the gas ovens were probably too small for the amount of food being cooked, so they did not reach a temperature high enough to kill the bacteria.

Three years ago, the Government's Advisory Committee on the Microbiological Safety of Food produced a report on the dangers posed by bacteria such as S. enteritidis in eggs. It included clear guidelines on the handling and storage of eggs. However, these need to be supplemented by advice specifically directed at campers. Meanwhile, people holidaying outdoors should use cold boxes to carry eggs, and should not prepare lightly cooked egg products under field conditions. Safer still, give up eggs completely for a few days.

PROMOTED VIDEO
News
Lane Del Rey performing on the Pyramid Stage at Glastonbury 2014
people... but none of them helped me get a record deal, insists Lana Del Rey
Arts and Entertainment
Dwayne 'The Rock' Johnson stars in Hercules
filmReview: The Rock is a muscular Davy Crockett in this preposterous film, says Geoffrey Macnab
News
i100
Arts and Entertainment
British author Howard Jacobson has been long-listed for the Man Booker Prize
books
Life and Style
tech
Arts and Entertainment
Standing the test of time: Michael J Fox and Christopher Lloyd in 'Back to the Future'
filmA cult movie event aims to immerse audiences of 80,000 in ‘Back to the Future’. But has it lost its magic?
Sport
Louis van Gaal watches over Nani
transfers
Arts and Entertainment
Flora Spencer-Longhurst as Lavinia, William Houston as Titus Andronicus and Dyfan Dwyfor as Lucius
theatreThe Shakespeare play that proved too much for more than 100 people
News
exclusivePunk icon Viv Albertine on Sid Vicious, complacent white men, and why free love led to rape
Sport
New Real Madrid signing James Rodríguez with club president Florentino Perez
transfersColombian World Cup star completes £63m move to Spain
News
ebookA unique anthology of reporting and analysis of a crucial period of history
Arts and Entertainment
Stir crazy: Noel Fielding in 'Luxury Comedy 2: Tales from Painted Hawaii'
comedyAs ‘Luxury Comedy’ returns, Noel Fielding on why mainstream success scares him and what the future holds for 'The Boosh'
Life and Style
Flow chart: Karl Landsteiner discovered blood types in 1900, yet scientists have still not come up with an explanation for their existence
lifeAll of us have one. Yet even now, it’s a matter of debate what they’re for
Arts and Entertainment
'Weird Al' Yankovic, or Alfred Matthew, at the 2014 Los Angeles Film Festival Screening of
musicHis latest video is an ode to good grammar. But what do our experts think he’s missed out?
Travel
Hotel Tour d’Auvergne in Paris launches pay-what-you-want
travelIt seems fraught with financial risk, but the policy has its benefits
Arts and Entertainment
booksThe best children's books for this summer
Independent
Travel Shop
the manor
Up to 70% off luxury travel
on city breaks Find out more
santorini
Up to 70% off luxury travel
on chic beach resorts Find out more
sardina foodie
Up to 70% off luxury travel
on country retreats Find out more
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Insight Analyst – Permanent – Up to £40k – North London

£35000 - £40000 Per Annum plus 23 days holiday and pension scheme: Clearwater ...

SQL Developer - Permanent - London - Up to £50k

£45000 - £50000 Per Annum 23 days holiday plus Pension scheme: Clearwater Peop...

Primary Teacher EYFS, KS1 and KS2

£85 - £130 per day: Randstad Education Preston: Randstad Education are urgentl...

KS1 and KS2 Primary NQT Job in Lancaster Area

£85 - £110 per day: Randstad Education Preston: Randstad Education is urgently...

Day In a Page

Noel Fielding's 'Luxury Comedy': A land of the outright bizarre

Noel Fielding's 'Luxury Comedy'

A land of the outright bizarre
What are the worst 'Word Crimes'?

What are the worst 'Word Crimes'?

‘Weird Al’ Yankovic's latest video is an ode to good grammar. But what do The Independent’s experts think he’s missed out?
Can Secret Cinema sell 80,000 'Back to the Future' tickets?

The worst kept secret in cinema

A cult movie event aims to immerse audiences of 80,000 in ‘Back to the Future’. But has it lost its magic?
Facebook: The new hatched, matched and dispatched

The new hatched, matched and dispatched

Family events used to be marked in the personal columns. But now Facebook has usurped the ‘Births, Deaths and Marriages’ announcements
Why do we have blood types?

Are you my type?

All of us have one but probably never wondered why. Yet even now, a century after blood types were discovered, it’s a matter of debate what they’re for
Honesty box hotels: You decide how much you pay

Honesty box hotels

Five hotels in Paris now allow guests to pay only what they think their stay was worth. It seems fraught with financial risk, but the honesty policy has its benefit
Commonwealth Games 2014: Why weight of pressure rests easy on Michael Jamieson’s shoulders

Michael Jamieson: Why weight of pressure rests easy on his shoulders

The Scottish swimmer is ready for ‘the biggest race of my life’ at the Commonwealth Games
Some are reformed drug addicts. Some are single mums. All are on benefits. But now these so-called 'scroungers’ are fighting back

The 'scroungers’ fight back

The welfare claimants battling to alter stereotypes
Amazing video shows Nasa 'flame extinguishment experiment' in action

Fireballs in space

Amazing video shows Nasa's 'flame extinguishment experiment' in action
A Bible for billionaires

A Bible for billionaires

Find out why America's richest men are reading John Brookes
Paranoid parenting is on the rise - and our children are suffering because of it

Paranoid parenting is on the rise

And our children are suffering because of it
For sale: Island where the Magna Carta was sealed

Magna Carta Island goes on sale

Yours for a cool £4m
Phone hacking scandal special report: The slide into crime at the 'News of the World'

The hacker's tale: the slide into crime at the 'News of the World'

Glenn Mulcaire was jailed for six months for intercepting phone messages. James Hanning tells his story in a new book. This is an extract
We flinch, but there are degrees of paedophilia

We flinch, but there are degrees of paedophilia

Child abusers are not all the same, yet the idea of treating them differently in relation to the severity of their crimes has somehow become controversial
The truth about conspiracy theories is that some require considering

The truth about conspiracy theories is that some require considering

For instance, did Isis kill the Israeli teenagers to trigger a war, asks Patrick Cockburn