Beware of lemon meringue pie
Microbe of the month: Bernard Dixon on the return of salmonella
Monday 15 April 1996
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.
- 1 BBC election debate: The one photo that summed up the whole 90-minute leaders debate
- 2 A bottle of wine a day is not bad for you and abstaining is worse than drinking, scientist claims
- 3 18th century sex toy found in 'toilet of sword fighting school' in Poland
- 4 'I wish my teacher knew...': Young students share their 'heartbreaking' worries in notes
General Election 2015: David Cameron catching up in polls – but he badly needs a clear lead
The Hubble Space Telescope's amazing journey 25 years on
South Africa xenophobic attacks: Shops looted and violence on streets of Johannesburg as foreigners are forced to hide in police stations
Earthworms rain down from skies over Norway, puzzling scientists
18th century sex toy found in 'toilet of sword fighting school' in Poland
The only black face in the Ukip manifesto is on the page about overseas aid
Ukip is the only main political party to not address LGBT rights in its manifesto
If I’m being racially abused I don’t need a white stranger with a saviour complex to rescue me
BBC election debate: The one photo that summed up the whole 90-minute leaders debate
Religion isn't growing, it is becoming vigorous in its demise, says philosopher AC Grayling
Russian warships in English Channel 'to conduct anti-aircraft and anti-submarine military drills'
£30000 - £40000 per annum + Benefits: Ashdown Group: Front-End UI Application ...
£18000 - £26000 per annum: Recruitment Genius: They work with major vehicle ma...
£27000 per annum: Recruitment Genius: Domestic Service Only Engineers are requ...
£23600 - £27500 per annum: Recruitment Genius: The Employability Service withi...