Science: Life in the time of cholera: a new fear of flying

The international flight, the seafood salad and Vibrio cholerae. Bernard Dixon tells a cautionary tale

In January 1991, for the first time this century, a cholera epidemic erupted in South America. Within a year, it had spread to 11 different countries, affected 400,000 people and killed more than 4,000 of them. The disease is still raging in that region.Butthebacterium responsible for cholera is a capable traveller, especially through water. That is why this month's Epidemiology and Infection contains a disturbing report of an outbreak of the disease contracted from food served on a passenger flight between Lima, Peru, and Los Angeles. Written by Richard Besser, of the University of California, and his colleagues, it describes the largest airline-associated epidemic of cholera ever recorded.

Most people infected by Vibrio cholerae do not become ill, especially if they are well-nourished and in good health. Nevertheless, the disease is understandably feared. It is a vile infection, largely attributable to a poison produced by V. cholerae, which causes diarrhoea so bad it can lead to death within hours. V. cholerae is invariably spread through contaminated water or food, only rarely passing from person to person.

The South American epidemic began in January 1991, when a Chinese grain boat brought the bacterium into Lima. Paradoxically, it was able to proliferate and spread there because the authorities had suspended chlorination of some of the city's wells. Their motive for doing so was to combat a far less tangible hazard associated with chemicals which may be formed when chlorine reacts with other substances in soil and water.

The recent incident came to lightwhentheLAhealth department received reports that bacteriologists had found V. cholerae in stools from five people who had been admitted to hospital with severe diarrhoea. One of the patients, a 70-year-old man, had died. All five had been passengers on a flight five days earlier, which had arrived in LA from Buenos Aires, calling at Lima en route.

Investigators set out to trace the other 331 people on the flight. They managed to locate 189 of them. Including the five who had been hospitalised, 100 of the passengers proved to be infected with V. cholerae. Seventy- five of them had also suffered from diarrhoea since arriving in the US. Ten had cholera and were treated accordingly.

All but one item of the food and drink consumed during the flight - including potentially suspect iced drinks and chicken sandwiches - were at most very weakly associated with infection. The exception was a seafood salad. It had been chosen by 87 per cent of the passengers whose stools contained V. cholerae, but only by 36 per cent of those who were free of the bacterium.

A caterer in Lima had prepared the salad, but how it becamecontaminatedis unclear. The most likely explanation is that the shrimps it contained were caught in waters containing V. cholerae and the bacterium had not been killed when they were cooked.

Before this incident, the biggest outbreak of cholera associated with airline travel occurred in 1972, when 47 passengers developed the disease after a flight from London to Sydney. Cold hors d'oeuvres, taken on board in a cholera-affected country, were the source of infection. The latest incident clearly demonstrates the risk associated with eating cold foods prepared in a place where cholera is raging.

Richard Besser and his co-authors strongly recommend that one conventional piece of advice, often given to travellers inareaswithinadequate hygiene and sanitation, should also be followed on flights originating from, or stopping in, such countries. This is to eat only foods that have been thoroughly cooked and are still hot.

"It is unlikely that the epidemic in Latin America will end soon," they conclude. "With thousands of airline passengers dispersing daily from cholera-affected countries, cholera outbreaks could easily occur in the US or other countries unaffected by the current pandemic." Indeed, one of the most disquieting aspects of the LA outbreak is that it attracted attention only because of its size and severity. Smaller outbreaks may have occurred, yet remained undetected. No doubt there will be others.