Shellfish consumption and awareness of risk of acquiring hepatitis A among Neapolitan families – Italy 1997

Reported by Giuseppe Salamina and Paolo D’Argenio on behalf of participants to a two week introductory course to the field epidemiology training course (PRO.F.E.A) – Region of Campania, Italy.

In 1996, about 15% of all reported cases of hepatitis A (n=8651) in Italy were from the Campania region, with Naples reporting the region’s highest incidence (34.9/100 000). Almost a half of all cases were between 15 and 24 years of age. In recent years, consumption of shellfish, particularly if raw or inadequately cooked, has accounted for 70% of reported cases of hepatitis A in Italy (1,2) and been implicated in several recent outbreaks of hepatitis A (3-5).

Shellfish are an important component of Neapolitan cuisine and a number of regulations and recommendations have been put forth to ensure that shellfish sold and eaten are free of hepatitis A and other pathogens. Details of the volume of shellfish consumption in Naples and the extent to which recommendations for their proper sale and safe consumption are followed, however, are not known. Such information is essential for planning health education and other prevention strategies.


As part of an epidemiology training course, a telephone survey of households randomly selected from the Naples telephone book was conducted in September 1997 to determine how often shellfish were eaten, how they were cooked, conditions under which the product was sold, and knowledge about hepatitis A and its transmission. Information was collected using a standardised questionnaire. Interviewers asked to speak with the person in charge of cooking or buying food for the family. ‘Family’ was defined as a group of one or more people who habitually ate at the same table in the household corresponding to the telephone number selected.


From the original 330 families selected (ten families for each interviewer), 72 (22%) were not reached and 46 (14%) refused to answer. A total of 329 interviews were completed by contacting additional families from a replacement list. Seventy-eight per cent of the participating families reported eating shellfish: 61% ate only cooked shellfish and 17% ate raw shellfish at least occasionally. During the month before the survey, 47% of the families had eaten shellfish at least once (46% cooked and 6% raw). Three quarters of those who ate cooked shellfish lightly cooked mussels or clams until the shells opened and then served them with pasta.

Interviewees from families that ate shellfish were significantly younger than those from families that did not: 45.8 vs. 58.9 years (p<0.001; Student’s t test). No difference was observed between the ages of respondents whose families ate only cooked shellfish and those who also ate raw shellfish. Shellfish consumption increased with the size of the household and respondents’ level of education, but these two associations disappeared when adjusted for age.

More than 95% of respondents had heard of hepatitis A and about three quarters believed that hepatitis A infection was common in Naples (table 1). Shellfish consumption did not vary significantly according to beliefs about frequency of occurrence of hepatitis A. About a third of respondents (113/329) were well-informed about specific diseases, including hepatitis A, that can be acquired through eating shellfish, but their eating habits were similar to those who were less knowledgeable. Perception of the severity of hepatitis A (i.e., whether or not respondents believed that admission to hospital was necessary) was not associated with shellfish consumption practices.

Table 1: Shellfish consumption and knowledge about hepatitis A. Naples, Italy, September 1997 (n=329)



Shellfish consumers

Mode of consumption







Think that in Naples hepatitis A is:

















do not know








Are aware that shellfish may be a vehicle for hepatitis A and other foodborne diseases

















Think that hepatitis A requires admission to hospital

never / sometimes
















do not know








Shellfish should be stored in refrigerated cases and sold in net bags on which a ‘use by’ date is clearly marked. Nonetheless, the 255 survey respondents from families that ate shellfish reported several inappropriate modes of storage and selling shellfish (table 2). Most commonly vendors sprayed shellfish with seawater or kept shellfish in washbasins containing seawater.Table 2: Inappropriate modes of storing and selling shellfish, reported by consumers. Naples, Italy, September 1997 (N=255)




sold by street vendors



sold loose



without an expiry date



not refrigerated



kept in or sprayed with seawater



The survey was limited to families with listed telephone numbers, therefore families of lower socioeconomic status were probably underrepresented. Nonetheless, the results confirmed that shellfish consumption is very common in Naples and suggested that raw shellfish was eaten more commonly than had been expected. Even cooked shellfish was often not cooked enough to inactivate hepatitis A virus. Respondents indicated that shellfish is often eaten with pasta in Naples. The shellfish are usually cooked just long enough for the valves to open (usually one or two minutes), which is not long enough to inactivate viruses. In mussels, for example, viral inactivation requires at least six minutes of cooking at 85-90°C (6).

The respondent’s age was the only factor associated with shellfish consumption, consumption being lower among the older respondents. In contrast, awareness of a high incidence of hepatitis A in Naples, knowledge about its route of transmission, and belief that it is a severe disease seemed not to affect shellfish consumption. Thus, information campaigns or other efforts to change Neapolitans’ shellfish cooking and consumption behaviours may be of limited value. Ensuring that the supply of shellfish is safe and uncontaminated may be more effective. One particularly risky vending practice is the sale of loose shellfish kept in large basins of seawater. This keeps them appearing fresh and appealing to customers. In Naples, vendors often pump their storage water directly from nearby ports, where the seawater is often contaminated with sewage. The use of such contaminated water is of particular concern since shellfish can rapidly concentrate bacteria and viruses (7,8). For example, mussels placed in water contaminated with viruses concentrate virus in their hepatopancreas, reaching maximal concentrations within two hours (7). Storage of shellfish in contaminated seawater has been identified as the route of contamination of shellfish responsible for an outbreak of cholera in the Mediterranean (8).

A well informed consumer could play a pivotal role in promoting practices that ensure the sale of uncontaminated shellfish products. Vendors who follow high quality procedures would be rewarded by increased business. The traditional local economy would be maintained and at the same time transmission of hepatitis A could decrease

Participants: A Avallone, M Agresti, VS Biancolilli, C Bova, M Barbato, T Coppola, V Carandente, AL Caiazzo, R Castiello, M Ciccozzi, MT D’Agostino, C De Crescenzo, E De Campora, G D’Antonio, M Episodio, MA Ferrara, L Ferrari, AS Lopreiato, M Loré‚ F Lonardo, A Marra, A Maffeo, MC Macchia, ME Prudente, V Pontieri, MG Panico, F Primiano, A Pecoraro, R Parrella, FA Porfido, B Russo, P Sardelli, A Saggese Tozzi.

Staff members of PRO.F.E.A: N Binkin, L Cafaro, G Capozzi, P D’Argenio, F De Stefano, G Fabbrocini, D Greco, T Manfredi Selvaggi, A Mele, A Parlato, G Salamina.

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4. Mele A, Catapano R, Cialdea L, Piscanc AM, Malden AS, Kresevic L et al. Outbreak of hepatitis A in Trieste (Italy). J Public Health Med 1994; 16: 242-4.

5. Malfait P, Lopalco PL, Salmaso S, Germinario C, Salamino G, Quarto M, et al. An outbreak of hepatitis A in Puglia, Italy, 1996. Eurosurveillance 1996; 1: 33-5.

6. Koff RS, Sear HS. Internal temperature of steamed clams. N Engl J Med 1967; 276: 737-9.

7. Croci L, De Medici D, Gabrieli R, Franco E, Di Pasquale S, Toti L. Effectiveness of water disinfection treatment on depuration of shellfish. Microbiolobie-Aliments-Nutrition 1992; 10: 229-32.

8. Greco D, Luzzi I, Sallabanda A, Didbra A, Kacarricy E, Shap L. Cholera in the Mediterranean: outbreak in Albania. Eurosurveillance 1995; 0: 1-2

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