In the Law Concerning the Prevention of Infectious Diseases and Medical Care for Patients of Infections (the Infectious Diseases Control Law), enacted in April 1999, both typhoid fever and paratyphoid fever are classified as Category II notifiable infectious diseases. All physicians who have diagnosed confirmed cases, suspected cases and asymptomatic carriers are requested to promptly notify the prefectural governor through the nearest health center. In compliance with the revision of the Enforcement Regulation of the Food Sanitation Law in December 1999, S. Typhi and S. Paratyphi A have been included as etiological agents of food poisoning. When food items are suspected to be involved in cases of typhoid and paratyphoid fever, investigations of food poisoning are required under the Food Sanitation Law. Furthermore, bacterial isolates from cases of typhoid and paratyphoid fever are to be submitted to the National Institute of Infectious Diseases (NIID) for detailed analysis. The Department of Bacteriology I performs phage typing and drug-susceptibility testing and provides results back to the prefectures. For disease trends up until 2000, refer to the preceding Topic of This Month (IASR 22:55-56, 2001).
The National Epidemiological Surveillance of Infectious Diseases (NESID): From 2001-2004, between 60-66 cases of typhoid fever occurred annually, without showing large increases or decreases (Table 1). Cases of paratyphoid fever decreased to as few as 20 in 2000, increased slightly to 22 in 2001, 35 in 2002, 41 in 2003, then sharply increased to 85 in 2004 (reported as of February 22, 2005). In 2004, the proportion of imported cases of typhoid and paratyphoid fever increased to 82% and 94%, respectively. Cases frequently occurred from April-May and from August-October (Fig. 1). Taking into consideration the incubation period and number of days from disease onset to diagnosis, it is estimated that acquisition of infection occurs during spring (February-April) and summer (July-September) vacations when people travel to endemic areas such as Southeast Asia and the Indian Subcontinent. The age distribution of cases of typhoid fever and paratyphoid fever indicates that the largest number of cases in the group of 20-39 years (Fig. 2), suggesting that students and office workers traveled overseas during long vacations such as spring and summer breaks (see p. 90 of this issue).
Countries where cases of typhoid and paratyphoid fever were presumed to have acquired infection from 2001-2004 are shown in Fig. 3. Typhoid fever acquired in Asia accounted for 71% of the cases; 57 cases in India, 35 in Indonesia, 16 each in Nepal and Bangladesh, 14 in Philippines, four each in Thailand and Cambodia, three each in China, Myanmar, Pakistan, and one each in Hong Kong, Taiwan, Laos, Afghanistan, Singapore, Sri Lanka, Turkey, Viet Nam. In addition, infection was acquired in Papua New Guinea, Marshal Islands, Mexico, Peru, Nigeria, and West Africa (1 case each). Paratyphoid fever infection acquired in Asia accounted for 90%; 55 cases in India, 29 in Indonesia, 24 in Nepal, 18 in China, eight in Myanmar, seven in Bangladesh, two each in Cambodia and Thailand, and one each in Sri Lanka and Viet Nam.
Phage type: Among the phage types of S. Typhi, E1 and D2 were predominant in both 2001 and 2002, while E1, A, and B1 were most common in 2003 and E9, E1, and B1 in 2004, demonstrating a slight change in phage type trends (Table 2). Strains imported from India in the past were mostly E1, but in 2004 E9 has appeared. The phage types of S. Paratyphi A were mostly 1 and 4 in 2001 and 2002, but in 2003 and 2004, a slight change was seen in phage type trends, as type 6 became predominant in addition to types 1 and 4 (Table 3).
Drug-susceptibility and treatment: Typhoid and paratyphoid fever are treated with fluroquinolones administered orally. In recent years, however, nalidixic acid (NA)-resistant strains to which fluoroquinolones are hardly effective have increasingly been detected in Japan (Fig. 4 and see p. 89 of this issue). Travel destinations of cases infected with NA-resistant strains have mainly been India, Bangladesh, and their neighboring countries. In typhoid and paratyphoid fever caused by infection with NA-resistant organisms, the febrile period is prolonged by the ineffectiveness of fluoroquinolones, resulting in prolongation of the therapeutic period (see p. 91 of this issue). For these types of cases, combination therapy with third generation cephalosporins may be indicated (see p. 90 of this issue).
Conclusion: Infection in endemic areas primarily occurs via consumption of water or uncooked food. In particular, consumption of unboiled water, ice, raw fish or shellfish, fruits, raw vegetables, half-cooked food, and unrefrigerated food items should be avoided. Thoroughly cooked food, hermetically sealed beverages, and peeled fruits and vegetables are generally considered safe to consume. Unless the safety of water is certain, boiled or commercial mineral water should be used for drink and tooth brushing. In recent years, cases have increased among long-term foreign residents of Japan who temporarily return to their home countries in Southeast Asia, the Indian Subcontinent or China, become infected there, and develop disease after returning to Japan.
Since necessity for surveillance of resistant organisms influencing therapy is increasing, we ask again that strains isolated from cases of typhoid and paratyphoid fever be sent to the National Institute of Infectious Diseases.