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A Foodborne Outbreak of Salmonella in the Province of Caserta, 2001

Reported by A. D’Argenzio, M. Trabucco, R. Graziano, and L. Verregia of the Epidemiology and Prevention Service of the Separtment of Prevention, Local Health Authority Caserta 2, Campania

 

On Wednesday, June 27, 2001, seven persons developed a severe gastroenteritis and were hospitalized at Cardarelli Hospital in Naples. All had participated in a party the previous Sunday in Mondragone, a small coastal town in the Province of Caserta in the Campania Region located approximately 40 km from the regional capital of Naples. The Epidemiology and Prevention Service of the Local Health Agency Caserta 2 was notified the day the cases were admitted, and they decided that further investigation of a possible food-borne outbreak was warranted.

 

The 12 people attending the party were interviewed within 72 hours of the first notification using a standardized questionnaire. Stool cultures were performed on hospitalized cases.

 

Two desserts were served at the party: tiramisù (a dessert containing mascarpone cheese and uncooked egg) and babbà mignon (small yeast-cakes soaked in rum). Orange soda and mineral water were also offered. The evening following the party, two portions of the tiramisù were given to a friend to bring home for her children. The tiramisù had been made from scratch, while the babbà were commercially prepared and were soaked in rum shortly before the party.

 

The day following the notification of the first case, samples were taken of leftover tiramisù from the refrigerator of the party’s host; all of the babbà had been consumed. None of the ingredients used to prepare the tiramisù remained, although the shop where the ingredients had been purchased was visited and samples were obtained of the mascarpone and the five different brands of eggs available.

 

A case was defined as a person who had developed diarrhea (more than 3 stools/day) or fever greater than 38 degrees C between Monday June 25th and Wednesday June 27 after having eaten the desserts served at the party. Ten of the 12 persons that attended the party became ill. The two children who had eaten the leftover portions of tiramisù on Monday the 26th also developed symptoms. Nine of the 12 cases (75%) were hospitalized.

The incubation periods are shown on the epidemic curve presented in the Figure. The median incubation period was 21 hours (range 9-62 hours).

 

Of the twelve persons who attended the party, two did not eat any of the desserts and consumed only mineral water. All of the remaining 10 had eaten the tiramisù, 8 had consumed orange soda, and 6 ate the babbà.  All those who ate the tiramisù became ill, for an attack rate of 100%.  The 6 persons who ate both tiramisù and babbà became ill, while the remaining four who ate tiramisù but not babbà also became ill.  Drinking orange soda was not associated with the illness. The two children who did not attend the party but who ate the leftover tiramisù the following day became ill. It was thus concluded that the likely vehicle was the tiramisù.

 

Of the 9 stool cultures on the hospitalized cases, 7 were positive for Group D Salmonella that was successively typed by the Istituto Superiore di Sanità as Salmonella enteritidis phage type 8B. The culture of the leftover tiramisù yielded the identical organism. The five brands of eggs that were sampled came from two different commercial farms. Eggs from both tested positive for the same phage type, and organisms were found both on the shells and in the egg yolks. The finding that eggs from two different farms were positive made it difficult to ascertain the original source of the transmission chain.

 

The tiramisù was prepared at home using raw eggs that were contaminated and mixed together with the mascarpone to form a pastry cream. When subjected to favorable conditions for growth (e.g., lack of refrigeration prior to consumption), pastry cream can form an ideal media for the growth of the organisms. Interviews of the person who had prepared the tiramisù failed to identify errors in its preparation and storage, although she may have been reticent to disclose such problems because she may have felt in some way responsible for the illness among her friends and relatives.

 

Acknowledgements: The authors wish to thank S. Sandrulli and M. Carullu (Experimental Zooprophylactic Institute of Southern Italy, Portici, Province of Naples), E. De Simone and S. Marino (Analytic Laboratory, Cardarelli Hopsital, Naples), R. Colella and A. Somma (Operative Unit, Population Prevention, District 47, Local Health Agency, Naples 1) for their collaboration in this study.

Figure: Temporal distribution of incubation period for the mondragone footborne outbreak, 2001.

 

Commentary

Ida Luzzi (Laboratory of bacteriology and medical mycology, ISS) and Alfredo Caprioli (Laboratory of Veterinary Medicine, ISS)

 

Salmonella enteritidis remains the serotype most frequently involved in outbreaks of foodborne illness and sporadic cases of gastroenteritis in industrialized countries. In the last 10 years, this organism and Salmonella typhimurium have accounted for 80% of all human isolates in the country.  While S. typhimurium represents an ubiquitous serotype and is isolated from many different animal species, the source of S. enteritidis isolations are almost always poultry and foods of avian origin:  meat, eggs, and egg products.

 

Since the mid-1980s, S. enteritidis has caused a true pandemic due to the contamination of the hens from farms that generate egg-laying stock. Vertical transmission of asymptomatic infection has occurred, resulting in rapid spread of the organism in many parts of the world. This spread is linked to the typically pyramidal structure of chicken farms, in which there is are a limited number of farms producing breeder stock that provide chicks to farms in a broad geographic area. Farms that produce eggs are in general subjected to less rigid controls than those done by law on breeder stock farms. Even when the prevalence of S. enteritidis in layer stock farms is low, foodborne outbreaks may still occur because of pooling of eggs during the preparation of certain foods.

 

In addition to preventive efforts directed toward eradication of the infection from the vertex to the base of the production pyramid and improvement of hygienic conditions in the preparation and conservation of foods, there is the need to conduct diligent surveillance of human infections. In the case of the salmonelloses, such surveillance is necessarily based on laboratory diagnosis and further requires the serologic typing of the isolates. In the case of the more common serotypes such as S. enteritidis, this should be followed by a more detailed typing such as phage or molecular typing.

 

There has been a surveillance system in place for several years in Italy designed to monitor enteropathogenic bacteria. Since1994, this system has participated in a European network known as ENTER-NET. In Italy, ENTER-NET is coordinated by the Istituto Superiore di Sanità and consists of a network of 29 microbiology laboratories.

 

For this system to be effective, it is important that infections, especially those of an epidemic nature, be notified in a timely manner and subjected to epidemiologic and microbiologic investigations that also include typing of the isolated strains. The laboratories of the ENTER-NET system are available to provide support to epidemic investigations. The list of the involved laboratories as well as information on the surveillance system and the data that it produces can be found on the web site of the ISS:
http://www.iss.it/laboratori/leb/enternet/salmo99.htm

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