The seventh cholera pandemic, which began in 1961 and has continued up to the present, is caused by V. cholerae O1, biovar El Tor. During this period, a large-scale cholera epidemic caused by V. cholerae O1 occurred in South America for the first time in 1991, while an epidemic due to a new V. cholerae O139 serotype occurred in India in 1992. In Japan, many cases of cholera infection often develop only mild watery diarrhea or soft stools. Nevertheless, cholera should be recognized as a disease characterized by severe watery diarrhea, and occasionally, death due to dehydration. Furthermore, persons with underlying disease may develop severe disease. In 2004, a 54-year-old male from Mie Prefecture who underwent a gastrectomy died of cholera due to V. cholerae O1, serotype Ogawa, biovar El Tor (see p. 6 of this issue).
Trends in cholera cases: As shown in Table 1, the annual number of reported cholera cases (including asymptomatic carriers) has remained at approximately 40 since enactment of the Law Concerning the Prevention of Infectious Diseases and Medical Care for Patients of Infections (the Infectious Diseases Control Law) in 1999, although figures have ranged between 15 in 2003 and 78 in 2004. The annual number of imported cases has been approximately 25. However, 67 cases were reported in 2004, among which many were returning travelers from the Philippines in June and July.
V. cholerae O1 is classified into two serotypes, Ogawa and Inaba. During 2000-2002, isolation of serotype Inaba was predominant (see IASR 23:219-220, 2002). Presumed countries where serotype Inaba infections were acquired were Thailand, Nepal, Singapore, China, Viet Nam, and Indonesia (Table 2). All isolates from 11 cases returning from Thailand were identified as serotype Inaba. During 2001 and 2002, 24 of 26 domestic cases were noticeably caused by serotype Inaba (Fig. 1). In 2003, serotype Inaba was isolated from 7 cases (all imported) (Table 2). All isolates from cases returning from India were serotype Ogawa. In 2004, serotype Inaba was predominantly isolated from travelers returning from Thailand, and was also isolated from four domestic cases. Moreover, serotype Inaba was isolated from six travelers returning from India, where serotype Inaba had not been seen up until 2003. In 2005, all 7 cases of serotoype Inaba were imported (India-3, Pakistan-2, Taiwan-1, Myanmar-1). In contrast, all nine domestic cases were serotype Ogawa (Fig. 1).
The ages of 37 domestic cases reported during 2002-2005 ranged 26-87 years (average: 59.5); most were 40 years and older, while 49% were 60 years and older. In comparison, the age range of 129 imported cases was 19-78 years (average: 43.2); 46% were under 40 years and 18% were 60 years and older (Fig. 2). Among the domestic cases, 10 occurred in Tokyo, eight in Chiba Prefecture, three each in Aomori, Kanagawa, Aichi and Mie Prefectures, and one each in Miyagi, Fukushima, Saitama, Ishikawa, Shizuoka, Hyogo and Okinawa Prefectures. All cases were sporadic in nature.
Trends in V. cholerae O139: According to a WHO report, V. cholerae O139 accounts for about 15% of V. cholerae (O1+O139) isolated in Asia, and for 83% (185 cases) and 59% (142 cases) of V. cholerae isolated in China in 2003 and 2004, respectively (see p. 16 of this issue, WER 80, No. 31, 261-268, 2005). In Japan, there were no reports of V. cholerae O139 for five years from September 1997, although in October 2002, V. cholerae O139 was isolated in Yokosuka City from a returning traveler from India (see IASR 23:315, 2002). In August 2004, V. cholerae O139 was also isolated in Yamagata Prefecture from two returning travelers from China (see p. 9 of this issue).
Cholera toxin (CT)-producing NAG Vibrio : Diarrheal disease due to NAG Vibrio is reportable as infectious gastroenteritis under infectious disease Category V of the Infectious Diseases Control Law, as well as food poisoning under the Food Sanitation Law. Since 2002, three domestic cases of cholera-like diarrheal disease due to CT-producing V. cholerae O141 (see p. 10 of this issue) and one domestic case due to CT-producing V. cholerae O8 (see IASR 25:10, 2004) have been reported. In addition, CT-producing V. cholerae O49 has also been isolated from food items (see p. 10 of this issue).
Conclusion: In 2005, a number of cholera cases were reported among returning travelers from Indonesia and the Philippines (see Table 2 and related information on p. 7 of this issue). Due to the fact that many cholera cases are identified among returning travelers from Asia (India, Philippines, Thailand, Viet Nam), sufficient precautions must be taken not to readily consume unboiled water or raw food when traveling to these areas. For preliminary reports of cholera activity overseas, ProMED information on infectious diseases for oversea travelers provided by quarantine stations of the Ministry of Health, Labour and Welfare (http://www.forth.go.jp/) is available.
After implementation of the Infectious Diseases Control Law, microbiological examination of fecal specimens from patients with diarrhea for the presence of V. cholerae is now conducted based on guidelines for V. cholerae testing (issued on September 28, 1988; see IASR 9:219-220, 1988). As shown in Table 1, reports of V. cholerae isolation from Public Health Institutes (PHIs) and quarantine stations account for about half of all reported laboratory-confirmed cases. This indicates that the isolated strains are not being sent to PHIs from clinical testing sites. Isolation of pathogens from cases and molecular epidemiological analysis of isolated strains are important for both cholera surveillance and investigations into causes of contamination (see p. 8 of this issue). Additionally, in order to better understand trends in cholera-like diarrheal disease by CT-producing NAG Vibrio , it is necessary to test for the presence of CT production or CT-encoding gene (ctx ). When V. cholerae is isolated at clinical testing sites, submissions of isolates to PHIs are desirable. For serotyping of NAG Vibrio , please consult the Department of Bacteriology I, the National Institute of Infectious Diseases. Because the possibility of a cholera-like epidemic caused by a new serogroup of V. cholerae exists, similar to the case of V. cholerae O139, it will be important to continue to closely monitor trends of CT-producing NAG Vibrio .