The Topic of This Month Vol. 30, No. 8 (No. 354)
Under the Law Concerning the Prevention of Infectious Diseases and Medical Care for Patients of Infections (Infectious Diseases Control Law), salmonellosis is included in the “infectious gastroenteritis”, a category V infectious disease to be reported as such by sentinel points (pediatric clinics in this case). Therefore, under the National Epidemiological Surveillance of Infectious Diseases (NESID), the number of salmonellosis patients is not available.
1. Incidence of food poisoning according to Statistics of Food Poisoning in Japan
In 1999, 11,888 (43%) of 27,741 patients of bacterial food poisoning were caused by Salmonella . While having decreased significantly since 2000, 2,053 (21%), 3,603 (28%) and 2,551 (25%) salmonellosis were reported among 9,666, 12,964 and 10,331 patients of bacterial food poisoning in 2006, 2007 and 2008, respectively (see p. 206 of this issue and IASR 29: 213-215, 2008). Salmonella remains in the top two causative agents of bacterial food poisoning to this day. In 2006-2008, number of patients involved in one Salmonella food poisoning outbreak was, in average, 16.6, 28.6 and 25.8 in the respective three years. Outbreaks involving more than 500 patients are generally considered as large-scale outbreaks. In 2007, there was one such incidence, which was caused by S . Enteritidis-tainted catered lunch (see p. 207 of this issue). Food poisoning due to Salmonella has seasonal variation with its peak in July-September (Fig. 1).
2. Laboratory findings in PHIs & HCs
1) Reports of Salmonella isolation: Until 1999, approximately 5,000 isolations of Salmonella were reported every year, but since 2000 the isolation number dropped significantly in parallel with the decrease of the Salmonella food poisoning. In 2006, 2007 and 2008, there were 1,104, 1,470 and 1,082 isolations (Fig. 2).
2) Serovars: There are more than 2,500 serovars in Salmonella . Among them, S . Enteritidis is the serovar most frequently isolated by PHIs and HCs from human specimens since 1989 (http://idsc.nih.go.jp/iasr/virus/bacteria-e.html). S . Enteritidis occupied 58% (3,830) of all the Salmonella isolates in 1996, but the percentage of S . Enteritidis among Salmonella isolates decreased gradually (Fig. 2), and in 2006-2008, it occupied 33% (360), 39% (576) and 32% (341) in respective years. As for S . Typhymurium that was isolated most frequently until 1988, there were 73 (6.6% of all the Salmonella isolates), 95 (6.5%) and 82 (7.6%) isolations in 2006, 2007 and 2008. As for S . Infantis that is frequently isolated from poultry, there were 67 (6.1%), 72 (4.9%) and 105 (9.7%) isolations in 2006, 2007 and 2008, respectively. As a consequence of the decrease in S . Enteritidis isolation (Fig. 2), other serovars are now becoming relatively frequent or even dominant in some areas, for example prevalence of S . Braenderup in Oita Prefecture (see p. 211 of this issue).
3) Outbreaks: Among outbreaks of salmonellosis reported by PHIs in 2006-2008, those involving more than 10 cases were 17, 20, and 25 in the respective years (Table 1). While there was a remarkable decline in the late 1990fs to early 2000fs, there has been no further decline in recent years (IASR 21: 162-163, 2000, 24: 179-180, 2003 and 27: 191-192, 2006). S . Enteritidis is the major serovar in the salmonellosis outbreak occupying 71% of the incidents in 2006, 70% in 2007, and 64% in 2008 (see IASR 28: 200-201, 300-301, 2007 and p. 209 & 210 of this issue). As for other serovars, S . Typhimurium caused one outbreak and S . Infantis caused three outbreaks in 2008. S . Saintpaul caused two or three outbreaks every year during 2006-2008.
As a rare case, soft-shelled turtles were incriminated in S . Typhimurium incidents in 2004 and 2007 (IASR 25: 261, 2004 and 29: 20-22, 2008).
3. Phage types (PT) of S . Enteritidis
Department of Bacteriology, NIID, has conducted phage typing of S . Enteritidis derived from outbreaks including familial ones (Table 2). PTs 1, 4, which were prevalent in 1990s, were continued to be isolated in 2006-2008. PT6a was most frequent in 2006, PT21 in 2007, and PT14b in 2008.
4. Salmonellosis in reptiles
In 2006-2008, there was no report of salmonellosis mediated by infected reptiles. However, public education on hygienic practices in raising such animals needs to be continued (see Notice of December 22, 2005 by the Tuberculosis and Infectious Diseases Control Division, MHLW), because, carrier rate of Salmonella is still significant among turtles in Japan (see p. 212 of this issue), and there was a multistate outbreak of turtle-mediated food poisoning in the USA in 2007 (MMWR 57: 69-72, 2008).
5. Conclusion and Comments
1) Salmonella food poisoning has decreased in recent years.
2) S . Enteritidis tends to cause serious systemic infection leading to death. In 2006, there was one such fatal case. Among 16 fatal cases of Salmonella infection encountered in 1996-2008, 14 were due to S . Enteritidis and 2 others were respectively due to S . Typhimurium and S . Haifa (see p. 206 of this issue). Patients with diarrhea accompanied by fever should consult physicians and receive appropriate treatment without delay (see p. 211 of this issue).
3) As hen's eggs are very frequently contaminated with S . Enteritidis, their handling needs special hygienic precaution. Special measures to prevent secondary infection from contaminated eggs and kitchen utensils should be taken. Handling of chicken meat needs caution as Salmonella -positive rate in chicken ground meat is still high (see p. 206 of this issue and Notice of March 30, 2009 by the Food Safety Division, MHLW). However, Salmonella contaminating the chicken meat is S . Infantis rather than S . Enteritidis, indicating that eggs and meat are infected through different routes.
4) In recent years, isolation of Salmonella serovars other than S . Enteritidis is becoming relatively frequent. Such serovars, e.g. S . Montevideo and S . Braenderup (IASR 29: 221-222, 2008 and see p. 211 of this issue), are often implicated in food poisoning whose source could not be identified in spite of geographical concentration of the patients.
5) Large-scale outbreaks were caused by fresh fruits and vegetables abroad (see p. 205 of this issue), and some such cases were caused by minor serovars, such as S . Tennessee and S . Saintpaul. An outbreak caused by S . Typhimurium-tainted peanut butter was reported in USA. Though some such butter was imported into Japan, adverse consequence was avoided by the prompt recall from the market upon information from the USA. In this case, pathogen information including genetic type shared among Japan and the USA facilitated the case investigation.
6) As food poisoning is globalizing, international information sharing on the food poisoning incidents and genetic data of causative agents is becoming more and more necessary from now. Such information sharing is now being facilitated through USA PulseNet and European CDC.
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