Eurosurveillance - Volume 8, Issue 2, 01 February 2003

Following the events of 11 September 2001, the ensuing spectre of bioterrorism and considerable efforts planning for the unthinkable (1), this Eurosurveillance issue reminds us of the continuing threat to public health from well-recognised pathogens, sometimes mistakenly judged to be controlled. Recently the incidence of salmonellosis has decreased substantially across the European Union, the number of cases reported to Enternet (2) declining from 100 267 in the peak year of 1997 to 73 006 in 2001 (I.S.T. Fisher - personal communication). However, recent events and the following articles illustrate continued challenges in salmonella control.

In the Netherlands Salmonella Paratyphi B variant Java increased in poultry from less than 2% of all isolates before 1996 to 60% in 2002. Despite exposure to contaminated meat is high, human patients with Java infection are rare (0.3% of all isolates). However, 50% of the human isolates showed PFGE profiles identical to the poultry clone. Resistance to flumequin in S. Java increased from 3% between 1996-2000 to 19% in 2001, and 39% in 2002, while that of other serotypes in poultry remained at about 7%. S. Java is also fast becoming less sensitive to ciprofloxacin.

PFGE analysis of S. Java strains (29 from humans, 30 from poultry meat) showed two major clusters. All isolates from poultry imported from the Netherlands belonged to Cluster A, which also comprised 10 human isolates. Thirty-one of the 37 isolates in this cluster had an identical JavX1 pattern, similar to the X8 profile of a particular S. Java clone predominant in poultry production in several European countries. Cluster B comprised 19 human isolates and two poultry isolates of unknown origin. These results combined with epidemiological data and information on the origins of poultry meat strongly suggested that imported poultry meat is an important source of Java infections in humans in Scotland.

The Enter-net surveillance system received results of antimicrobial sensitivity tests for isolates from over 27 000 cases of human salmonellosis in 2000 in 10 European countries. Almost 40% of isolates were resistant to at least one antimicrobial, with 18% multiresistant. Resistance to ampicillin, streptomycin, sulphonamides and tetracyclines was common, with over 20% of isolates resistant to at least one of these antimicrobials. Clinical resistance to ciprofloxacin was rare, with only 0.5% of isolates exhibiting such resistance (MIC >1.0 mg/l). Resistance to nalidixic acid coupled with a decreased susceptibility to ciprofloxacin (MIC 0.25-1.0 mg/l) was more common, with 14% of isolates showing these properties. Resistance to third-generation cephalosporins was rare with only 0.6% of isolates resistant to cefotaxime. In all countries multiple resistance was most common in Salmonella enterica serotype Typhimurium, with 51% of isolates multiresistant in total. In England and Wales multiple resistance was also prevalent in S. Virchow and S. Hadar, whereas in other countries multiple resistance was common in serotypes such as S. Blockley.

An external quality assessment of PFGE method to discriminate between salmonella serotypes and lysotypes was carried out by the Salm-Gene project in Europe. A set of 16 strains of S. Enteritidis was sent to 9 national salmonella reference laboratories. By using a harmonised protocol, the PFGE profiles produced were comparable between each centre. In most cases, there was at least 90% similarity between isolates tested in the different European laboratories and there was usually >95% similarity. This suggests that PFGE analyses are reproducible and therefore can be used as a valuable investigation tool combined with epidemiological data.

The incidence of Salmonella enteric infections in Gipuzkoa, Spain, was estimated by studying a stable population between 1983 and 2000. Only stool culture confirmed cases were included. The annual mean rate of infection in children under 2 years old was 1121 per 100 000 (CI 95%; 1060-1181). This age group had the highest relative risk (RR), 16.2-fold higher than the RR of those aged over 14 years. Salmonella Enteritidis was the most prevalent serovar (80.4% of all patients), followed by Salmonella Typhimurium (11.7%).