Bollettino epidemiologico nazionale

Gastroenteritis Outbreak Following a Wedding Banquet in Modica, Sicily

Giuseppe Ferrera, Angela Bianco, and Francesco Blangiardi, Local Health Agency 7, Ragusa

On the 17th of September 2001, the Maggiore Hospital of Modica in the province of Ragusa in southeastern Sicily reported a case of gastroenteritis to the local public health office in a 17 year old adolescent who had attended a luncheon wedding banquet on the 13^th of September at 2 PM. Her symptoms, which began on the 13^th at approximately 11 PM, consisted of diarrhea, fever, and vomiting. Because of the persistence of her symptoms, she was admitted to the hospital on the 15^th of September.

The case notification arrived in the public health office in Ragusa on the 19^th, and an investigation was initiated to determine whether this was an isolated case or was possibly associated with attendance at the wedding banquet. The index case was asked to provide information on how to contact the family of the newlyweds. The groom was contacted on the afternoon of the 19^th, and he reported that several of the guests had felt ill, complaining primarily of diarrhea. Informed of the public health importance of the situation, he provided a list of the guests and their telephone numbers. On the afternoon of the 19th, the list of foods served at the wedding reception was obtained from the restaurant.

The following operational case definition was employed: All persons who attended the wedding banquet on the 13^th of September and who had diarrhea with at least 3 stools in a 24-hour period (with or without abdominal pain or fever) with onset the evening of the 13th or during the three subsequent days.

A standardized questionnaire was developed that included information on signs and symptoms and the foods consumed during the banquet. On the afternoon of the 20^th, personnel from the public health office of Modica conducted telephone interviews of those who had attended the banquet.

A total of 122 of the 185 participants were interviewed. Five of the attenders had not eaten anything and did not become ill; for this reason, they have been excluded from subsequent analysis. Among the 117 that did eat, 58 became ill, yielding an attack rate of 49.6%.

Symptoms consisted of watery mucous diarrhea (49%), abdominal cramps (37%), vomiting (11%), and fever (5%). The symptoms lasted an average of 48 hours. The epidemic curve is shown in Figure 1.

The food-specific attack rates and differences between rates are shown in Table 1. The foods for which there was the greatest difference in attack rates between those who ate and who did not eat a specific food were seafood salad, grilled swordfish, and bowtie pasta with arugula (rocket) and shrimp. Among the 7 participants that did not either the seafood salad or the swordfish, none fell ill, even though they had eaten other dishes. By contrast, 3 of the 13 (19%) that ate only swordfish and 2 of the 8 (25%) who ate only swordfish, and 53 of the 86 (62%) who ate both became ill.

Two foods were therefore suspected: the seafood salad, which had been prepared with shrimp, octopus, and mussels, some of the latter of which were steamed open and served in their shells and others of which were removed from their shells or were covered with bread crumbs and cooked on the half shell in the oven. The swordfish was cooked on a hot grill and served immediately.

Because the restaurant prepared and served two other wedding banquets on 12^th and the evening of the 13^th, the menus from these events were obtained and the families of the newlywed were contacted. Among the estimated 330 guests in attendance at these two events, none had complained of any symptoms.

An inspection of the restaurant was performed to evaluate working procedures and to obtain any available samples of foods similar to those implicated in the epidemiologic investigation.

This outbreak of food-borne gastroenteritis was studied 6 days after the event. The epidemiologic investigation implicated two vehicles. Unfortunately, no fecal specimens were obtained from the patients, and it is therefore not possible to know which organism was implicated. From the symptoms (abdominal cramps, diarrhea), the incubation period (12-24 hours) and the foods involved, it is likely that this was a bacterial or viral illness, although in the absence of microbiologic findings, it is difficult to be more precise. Among the bacteria that could have caused the outbreak, the most likely are Vibrio parahemolyticus, E. coli, or Salmonella.

Comment

Stefania Salmaso, Laboratory of Epidemiology and Biostatistics, ISS

The above outbreak is without doubt an example of many others in which a single case of severe illness triggers an investigation, and many persons are found to have been exposed. The epidemiologic approach permitted the correlation of the onset of an illness with the consumption of two dishes served at a wedding banquet, even in the absence of microbiological data.

The results confirm the potential dangers of seafood, which during preparation usually undergoes heat treatment that is inadequate to guarantee its safety. In this case, the high attack rate suggests that the involved foods were highly contaminated and that they arrived in the kitchen of the restaurant already contaminated. Obtaining seafood from reliable sources is one of the most critical points in the prevention of food-borne outbreaks. Often the conditions in which the seafood is cultivated, harvested, transported, and stored are not ideal but are accepted out of habit. Procedures should be adopted to prevent outbreaks in settings such as restaurants that include avoiding the introduction of possibly contaminated foods.

Unfortunately, the investigation of this outbreak has a number of limitations, including the lack of microbiologic findings that makes it difficult to draw definitive conclusions about the etiology, the lack of information on the source of the materials used to prepare the various dishes, and detailed information regarding their preparation. Each outbreak like the one described here should constitute an occasion to examine the procedures adopted and identify critical deficits. The absence of information in this area prevents public health practitioners from taking advantage of the experience.