The Topic of This Month Vol.24 No.8(No.282)

Salmonellosis in Japan as of June 2003

(IASR 2003; 24:179-180)

According to the Statistics of Food Poisoning in Japan, the Ministry of Health, Labour and Welfare (MHLW), cases of bacterial food poisoning totaled at 27,741 in 1999, 32,417 in 2000, 15,753 in 2001, and 17,533 in 2002. Of these cases, salmonellosis accounted for 43% in 1999, 21% in 2000, 31% in 2001, and 33% in 2002. Except in 2000, when Staphylococcus aureus was the most predominant (see IASR, Vol. 22, No.8), Salmonella has generally been the most predominant etiological agent (Table 1). However, the number of food borne salmonellosis cases has recently been on the decrease, keeping fewer than 7,000 per year since 2000. The number of cases per incident of Salmonella food poisoning was 14.4 in 1999, 13.4 in 2000, 13.7 in 2001 and 12.5 in 2002. The number of cases per incident involving two or more cases was 34.6 in 1999, 22.3 in 2000, 23.8 in 2001 and 32.0 in 2002. Of those incidents, two in 1999 and three in 2002 each involved as many as more than 500 cases (Table 2). Many incidents occurred in summer, with a peak in August-September (Fig.1).

The reports of Salmonella isolation from the prefectural and municipal public health institutes (PHIs) to the Infectious Disease Surveillance Center (IDSC), the National Institute of Infectious Diseases (NIID) numbered at 5,000 to 6,000 per year before 2000 (Fig. 2), however, the reports of Salmonella isolation as well as the number of salmonellosis cases were showing a tendency of decrease (Table 1). Since 1989, Salmonella enterica subsp. enterica serovar Enteritidis (S . Enteritidis) has been the most predominant serovar (Table 3). It accounted for 46% in 1999, 55% in 2000, 53% in 2001, and 62% in 2002. These figures were 10 times larger than those of the second-ranked ones (except in 1999). However the reports of S . Enteritidis isolation decreased to 1,302 in 2002, one-third of the peak value in 1996 (3,830) (see

S . Typhimurium, which used to be the most predominant serovar until 1988 (see IASR, Vol. 16, No.1, Vol. 18, No. 3 and Vol. 21, No. 8) ranked 5th in 1999, 2nd in 2000, 3rd in 2001, and 4th in 2002. In Western countries, multidrug-resistant S . Typhimurium, for example, definitive phage type (DT) 104 resistant mainly to ampicillin, chloramphenicol, streptomycin, sulfonamide, and tetracycline, is now prevalent (see IASR, Vol. 21, No. 11 and Vol. 22, Nos. 9 & 10). S . Typhimurium DT104 and its related types have also been isolated in Japan since 1986, but not showing a sudden increase as was S . Enteritidis (Fig. 3). Since the first isolation of fluoroquinolone- resistant S . Typhimurium in 2000, isolation of similar strains have been reported and attention must be paid to the future trend (see page 181 of this issue).

Another serovar, S . Oranienburg, increased suddenly in 1999 (Table 2) due to a diffuse outbreak of food poisoning caused by consumption of semidried squid. Thereafter, isolation of S . Oranienburg decreased becoming to a rank lower than the 15th in 2002 (Table 3).

The number of outbreaks caused by Salmonella is also on the decrease. Among the outbreaks reported to IDSC during 2000 through 2002, those involving 10 or more cases numbered 64 in 2000, 36 in 2001, and 37 in 2002 (Table 4). Five to 11 different serovars of Salmonella spp. were found to be involved in the causative strains of these incidents (see IASR, Vol. 21, No. 11, Vol. 22, Nos. 2, 5 and 11, Vol. 23, No. 3, Vol. 24, No. 3 and page 182 of this issue). S . Enteritidis accounted for 77% in 2000, 56% in 2001, and 84% in 2002, of all Salmonella food poisoning outbreaks. Outbreaks of S . Enteritidis infection are often attributed to contaminated eggs or egg dishes; secondary contamination of other foods is also another important route of infection (see IASR, Vol. 18, No. 9 and Vol. 23, No. 4). To prevent food poisoning due to eggs and egg dishes contaminated with S . Enteritidis, the enforcement regulation of the Food Sanitation Law was partially amended in October 1998. In compliance with the amendment, it has been obliged to display the best before date on packages of shell eggs, and guidelines on cooking eggs, processing egg products, and pooling eggs were instituted. In addition, the MHLW released a manual for hygienic management of trader houses for egg inspection and packaging eggs, and a recommendation on "safe consumption of eggs at home". These general countermeasures as a whole could have contributed to the decreased incidence.

S . Enteritidis strains sent to the Department of Bacteriology I, NIID, were subjected to phage typing. The results with the strains derived from outbreaks including familial infections from 1999 to 2003 are shown in Table 5. Phage type (PT) 4 was the first rank, accounting for 35% in 1999, 27% in 2000, 26% in 2001, and 30% in 2002, followed by PT1 as the second rank (26% in 1999, 21% in 2000, 19% in 2001, and 18% in 2002). The prevalence of PT1 and PT4 was on the gradual decrease, while that of PT47 was on the increase to 14% in 2002, and other PTs and RDNC have also often been isolated.

In 2002, there were two deaths (one male and female each) from S . Enteritidis food poisoning. Salmonella causes not only enteric infection with only diarrhea, but also such systemic infection as sepsis. It is, therefore, important to seek medical assistance in early stage and, for the doctor, to pay careful attention to any possible change in patients' conditions. As stated above, Salmonella food poisoning has been on the decrease, but several large-scale outbreaks still occurred last year as shown in Table 2. Medical and public health personnel are required to pay attention to the prevalence of Salmonella food poisoning and the serovars of the organisms involved. It is important to give information to food handlers and consumers on the effective preventives of food poisoning. Proper precaution should be taken especially against storing and handling food materials for the forthcoming summer.

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