The Topic of This Month Vol.27 No.8(No.318)

Salmonellosis in Japan as of June 2006

(IASR 27: 191-192; August, 2006)

Salmonella surveillance in Japan consists of (1) notification of food poisoning in compliance with the Food Sanitation Law [the Food Safety Division, the Ministry of Health, Labour and Welfare (MHLW), the Statistics of Food Poisoning in Japan], and (2) the reports of Salmonella isolation (Infectious Agents Surveillance Report) based on the surveillance for etiological agents conducted at prefectural and municipal public health institutes (PHIs) and health centers (HCs) on cases of food poisoning outbreaks. In addition, the Department of Bacteriology I, the National Institute of Infectious Diseases (NIID) conducts phage typing of isolates of Salmonella enterica subsp. enterica serovar Enteritidis (S . Enteritidis) as a part of the pathogen surveillance. Under the National Epidemiological Surveillance of Infectious Diseases (NESID) in compliance with the Law Concerning the Prevention of Infectious Diseases and Medical Care for Patients of Infections (Infectious Diseases Control Law), food poisoning and related diseases are included in infectious gastroenteritis in the category V infectious diseases reported by pediatric sentinel clinics and no individual reporting is being made as a salmonellosis.

Incidence of food poisoning: Cases of bacterial food poisoning in the Food Poisoning Statistics in 2003-2005 numbered at 16,551, 13,078 and 16,678. Of these figures, salmonellosis cases numbered respectively at 6,517, 3,788 and 3,700. The decreasing tendency during these two years is obvious, although the number of salmonellosis cases has been seated at the top among cases by bacterial agent during this period (see IASR, 27: 169, 2006). The average number of cases per outbreak in each year has been counted at 18.6, 16.8 and 25.7. No incident involving more than 500 cases, a standard scale of large-scale outbreaks as a special target for countermeasures, has occurred during these three years. The incidence of salmonellosis peaked in the summer season, July-September (Fig. 1).

Laboratory findings in PHIs & HCs

1) Reports of Salmonella isolation: The number of Salmonella isolation used to count at approximately 5,000 until 1999, whereas those after 2000 were on the decrease reaching approximately 1,300 both in 2004 and 2005 (Fig. 2).

2) Serovars: S . Enteritidis has been the top serovar since 1989 among Salmonella isolates from human sources (see, the ratio accounting for 62% in 2002, 62% in 2003, 47% in 2004 and 50% in 2005 (Table 1). As S . Enteritidis decreased all Salmonella serovars were also on the decrease (Fig. 2). Salmonella organisms usually give positive results in the lysine-decarboxylase test, one of biochemical tests for identification. Attention must be paid to the test as S . Enteritidis strains showing negative results in the test have been reported (see IASR 25: 154-155, 2004 & 26:93-94, 2005).

On the other hand, S . Typhimurium, which used to hold the top position until 1988, was at the second in 2003 and at the third position in 2004 and 2005. After 2000, approximately 20 fluoroquinolone-resistant S . Typhimurium strains have been reported. Continuous attention must be paid to infections with such strains, as they may show resistance to the chemotherapy (see IASR 24:179-182, 2003). Among other serovars, S . Infantis has occupied an upper position. It has been reported that most Salmonella isolated from domestic chicken meat were S . Infantis and those from imported chicken meat S . Enteritidis (see. p. 193 of this issue).

3) Outbreaks: Salmonellosis outbreaks reported during 2003-2005 counted at 60, 32, and 31 in each year, of which those involving more than 10 cases were counted at 42, 23, and 26, respectively (Table 2). They were apparently on the decrease when compared with those in the 1990fs (see IASR 21:162-163, 2000 & 24:179-180, 2003). The proportion of incidents caused by S . Enteritidis accounted for 76% in 2003, 78% in 2004, and 54% in 2005. There were two relatively large-scale incidents: one was caused by S . Typhimurium involving 358 cases in 2003 (see IASR 25:99-100, 2004) and the other by S . Infantis 366 cases in 2004 (see IASR 25: 303-304, 2004), and both were caused by catered lunch.

The causative food materials often involved henfs eggs as often seen in S . Enteritidis incidents (see IASR 25:79, 2004). As a rare case, soft-shelled turtles were incriminated in an S . Typhimurium incident (see IASR 25: 261, 2004). An incident suspected of secondary contamination from henfs eggs through kitchen utensils has been reported (see IASR 24:267, 2003).

Phage types (PT) of S . Enteritidis: Phage types of S . Enteritidis derived from outbreaks including familial infection and sent to the department of Bacteriology I, NIID, are shown in Table 3. PT4, which used to be at the top position, were found in 28 incidents in 2002, in 24 incidents in 2003, in 14 incidents in 2004 and in 8 incidents in 2005, showing a tendency of decrease. PT1 and PT47 also decreased respectively to 9 and 7 incidents in 2005. On the other hand, PT14b, which was found in 2 incidents in 2002, increased to 9 incidents in 2005, thus phage types are showing diversity. Many of lysine-decarboxylase test negative strains described above were typed as PT14b or PT4.

Salmonellosis in reptiles: In 2004-2006, salmonellosis cases with sepsis and meningitis were reported for which pet animals, turtles, a tortoise and an iguana, were suspected to be the sources of infection (see IASR 26: 342-343 & 344-345, 2005, 27:71-72, 2006 and p. 203 of this issue). The etiological organisms were S . Braenderup, S . Paratyphi B, S . Schlessheim, S . enterica subsp. arizonae 45:g, z51:-, and S . Poona. In food poisoning, a certain serovars such as S . Enteritidis are involved, while in cases caused by reptiles, a variety of serovars are isolated. Not only mammalians but also many other species of animals are the reservoirs of Salmonella , so adequate educational activities such as hygienic precautions in raising animals are necessary (see Notice of December 22, 2005 by the Tuberculosis and Infectious Diseases Control Division, MHLW).

Conclusion: Recently outbreaks of salmonellosis are on the decrease, however, one death occurred by S . Haifa in 2004 (see IASR 26:19-20, 2005), and also in July 2006, a 9-year-old child died of S . Enteritidis infection. Salmonella develops not only enteric infection such as diarrhea but also sometimes causes severe systemic infection. If diarrhea accompanies fever, it is necessary to consult a doctor as early as possible and enough attention must be paid to any change in conditions.

Since the results of a survey on food contamination with etiological bacteria of food poisoning showed a high Salmonella -positive rate in chicken ground meat (see Notice of March 17, 2006 by the Food Safety Division, MHLW), sufficient attention must be paid to handling of not only henfs eggs but also chicken meat. Although no such a case has occurred in Japan, outbreaks in wide areas of S . Enteritidis infection due to almonds of US products, which were also imported to Japan, have been reported in US and Canada in 2004 (see MMWR, 53: 484-487, 2004). It is important to keep on paying attention to the incidence of salmonellosis inside and outside of Japan and to the tendency in prevalent serovars, together with thorough hygienic control for prevention of food poisoning and infection.

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