Salmonella in Alfalfa Sprouts

Salmonella in alfalfa sprouts

The Lancet

Volume 345

February 18, 1995

sir-Theenlarging international food trade and processing of large quantities of food have increased the number of foodborne infections in many countries. There are examples showing that these epidemics may spread across national borders, as happened in the early 1980s, when chocolate bars originating from Italy caused an epidemic due to Salmonella napoli in England and Wales.1 In 1973-74, 5 eastboume infection in the USA and Canada was also traced back to contaminated chocolate.2 We report an epidemic due to .S bovismorbificans, which originated fromAustralian alfalfa seeds and was observed concomitantly in Finland and Sweden.

In the middle of March, 1994, several people on the west coast of Sweden contracted S bovismorbificans, a serovar that is very rare in Sweden. The Swedish Institute for Infectious Disease Control contacted their Nordic neighbours but no cases due to this serovar were seen in Norway, Denmark, or Finland. An epidemiological investigation in Sweden showed that the infection could be traced to alfalfa sprouts from onesprouting plant. On March 28, a consumer complained of having bought a mixture of sprouts with a bitter taste from a retail shop in Helsinki. Examination in the food inspection laboratory revealed S bovismorbificans. This serovar has since been isolated several times from alfalfa sprouts grown from the same lot of seeds. The lot originated from Australia, and had been exported to Sweden, and then to Finland. An increase of incidence of S bovismorbificans infections was observed in the Helsinki region about two weeks after the beginning of the Swedish epidemic. The number of bacteriologically verified cases was 210 in Finland and 103 in Sweden. The infected seeds were confiscated and destroyed, and people were warned through the media.

During May, 1994, the number of domestic cases of S bovismorbificans increased again in Sweden, and was traced to another production plant. This production plant used the seeds from the same importer that were probably from the same lot again. This was not the end of story, since new cases occurred during the summer in Stockholm. The production plants involved were decontaminated. Up to the end of November, the total number of infections due to S bovismorbificans originating from alfalfa sprouts in Sweden was 282.

The Finnish production plant involved was decontaminated, as checked by sampling. The routine antimicrobial treatment of seeds with a solution of 0-5% sodium hypochlorite for 45 minutes did not prevent the epidemic. Because alfalfa sprouts are tender, they are eaten raw, and the potential pathogenic bacteria are viable. Thus, the seeds should be pasteurised before sprouting or the sprouts heated sufficiently before eating. Increased use of living food increases microbiological risks. Long retail shelf-life, especially on insufficiently cool shelves, further increases these risks. The present epidemic was the third one due to sprouts contaminated with salmonellae in Finland in the 1990s.

Our experience shows that salmonellae cannot be cultured from the seeds but only after sprouting; thus, the cultures made by customs based on random sampling of seeds have not revealed contamination with salmonellae. Salmonella in sprouts of various plants have been reported from at least three countries.3-5 For example, in Thailand nearly 9% of bean sprouts are contaminated with salmonellae.4 With the decrease or disappearance of inspections at borders, food inspection authorities are confronted with a challenge to prevent multinational epidemics spread by a variety of foods.

*Antti Ponka, Yvonne Andersson, Anja Siitonen,Birgitta tie Jong, Matt/Jahkola, Oil! Haikala, Aimo Kuhmonen, Pekka Pakkala

•Helsinki City Centre of the Environment. 00510 Helsinki, Finland;

Swedish Institute for Infectious Disease Control; National Public Health Institute,

Helsinki; and National Food Administration, Helsinki

  1. Gill ON, Sockett PN, Bartlett CLR, et al. Outbreak of Salmonella napoli infection caused by imported chocolate bars. Lancet 1983; I:574-77.

  2. Craven PC, Mackel BC, Baine WB, et al. International outbreak of Salmonella eastboume infection traced to contaminated chocolate. Lancet 1975; i:788-92.

  3. Andersson Y, de Jong B. Again an outbreak originating from sprouts. EpidAktuellt 1994; 17: 10 (in Swedish).

  4. Jetngklinchan J, Saitanu K. The occurrence of salmonellae in bean sprouts in Thailand. Southeast Asian 3 Trap Med Public Health 1993; 24: 114-18.

  5. O'Mahony M, Cowden J, Smyth B, et al. An outbreak of Salmonella saint-paid infection associated with bean sprouts. Epidemiol Infect 1990; 104: 229-35