Bollettino epidemiologico nazionaleSalmonella Surveillance in 2000: The Italian ENTER-NET System
Simona Gorietti1 and Luca Busani2 on behalf of the Gruppo ENTER-NET Italia: Alfredo Caprioli2, Ida Luzzi3, Tiziana Pichiorri1, Giuliano Siepi1, Alberto Eugenio Tozzi1 and the directors of the microbiology laboratories participating in the surveillance system
1Laboratory of Epidemiology and Biostatistics, 2Laboratory of Veterinary Medicine, and the 3Laboratory of Bacteriology and Medical Mycology, Istituto Superiore di Sanità, Rome
An estimated 12,000 cases of Salmonella occur annually in Italy, representing an important public health problem both in terms of morbidity and costs (1). To monitor potential spread beyond the borders of individual countries, the ENTER-NET surveillance system was launched. The system currently includes 23 European and 3 non-European countries. In each country, reference laboratory microbiologists and public health epidemiologists working at national level serve as country coordinators.
Italy has participated in ENTER-NET since 1997. The Italian network consists of 29 referral laboratories (2), coordinated by the Istituto Superiore di Sanità (ISS). At international level, the project is coordinated by the Public Health Laboratory Service (PHLS) Communicable Disease in London.
The primary objective of ENTER-NET is to monitor trends in Salmonella, E. coli O157 and other E. coli that produce vero-cytotoxins (VTEC), and other enteric pathogens as well as trends in antibiotic resistance of these organisms. These data can be used to compare the epidemiology of food-borne infections across countries and to recognize national and/or international outbreaks in a timely fashion. Serotyoping is performed to facilitate identification of possible outbreaks, and data are rapidly forwarded to a common central data base (3).
The involved laboratories conduct isolation of Salmonella, E. coli O157, and other enteric pathogens from human and non-human sources and assemble epidemiologic and clinical information on the source of the isolate as well microbiologic data including antibiotic susceptibility. These data are sent to the ISS each month so that they can be analyzed in a timely fashion. The ISS conducts an analysis of the data to identify unusual temporal or spatial clusters of specific serotypes of Salmonella and evaluates the regional and national trends for the reported isolates. Periodically, these data are sent to the PHLS, and feedback is provided to participating laboratories in the form of special alerts sent via e-mail concerning unusual findings, periodic reports, and the Internet (www.iss.it/laboratori/leb/enternet/enternetalia.htm).
To date, Salmonella species account for the vast majority of notifications in Italy. In 2000, 19 peripheral and referral laboratories were involved in Salmonella reporting and notified a total of 10,864 isolates, of which 55% were from human sources, 10% were from animal sources, and 34% were from foods or the environment (Table 1). The number of non-human isolates in 2000 was nearly double that reported in 1999, while the isolates from unknown sources declined from 1.5% to 0.7%. Reporting was not uniform; most (71%) of the isolates were from Northern Italy. As is typically seen with Salmonella, isolations were more common during the summer and early fall (Figure).
S. enteriditis was the most common human isolate, while S. typhimurium, was the most ubiquitous, accounting for 31% of human, 25% of animal, 24% of food, and 16% of environmental isolates.S. Derby, S. Bredeney and S. Blockley were also ubiquitous but were less common. By contrast, other serotypes appear to occupy specific ecologic niches with limited reservoirs of infection.
During 2000, collection of data on the strains of Salmonella circulating in Italy has permitted the description of seasonal trends and comparison of Italian data with those of other countries. In addition, it has provided information on the ecology of various serotypes through the comparison of the frequency of different serotypes from humans, animals, foods, and the environment. During the course of the year, ENTER-NET also collected information on other enteric pathogens, including Campylobacter spp. and VTEC. Nonetheless, with respect to the objectives originally established, ENTER-NET does not produce information on the incidence of infections and is not able to identify epidemics in a timely manner because of problems in gathering and transmitting data, even though special alert bulletins sent out during “unusual” situations have served to increase awareness of the involved laboratories about the potential uses of the system to identify outbreak situations.
Recently, a workshop was held at the ISS that was attended by the participants in the Italian network, during which the critical points in the system were examined and changes were planned in the system to improve its functioning. Despite its current limitations, ENTER-NET Italia represents a concrete example of the role that a national surveillance system can play as part of a broader European network.
References
1. Demicheli V et al. “The Emilia costing study: valutazione dell’impatto economico della salmonellosi umana”. MECOSAN 1994; 11:8-15.
2. Tozzi AE, Gorietti S, Pichiorri T e il Gruppo di lavoro ENTER-NET Italia. Sorveglianza delle infezioni da patogeni enterici: l’esempio di ENTER-NET. Microbiologia Medica 2001; 16(1):114-117.
3. Fisher IST, on behalf of the Enter-net participants. The Enter-net international surveillance network - how it works. Eurosurveillance, 1999; 4(5):52-55.
