The Topic of This Month Vol.17 No.12(No.202)
Cases of typhoid and paratyphoid fever are reported by the public health department of each prefecture to the Ministry of Health and Welfare; S.Typhi and S.Paratyphi A isolated from patients and carriers are sent off to the National Institute of Health (NIH). The Laboratory of Enteric Infection II, the Department of Bacteriology, NIH, examines the isolates for the phage type (PT) and drug sensitivity and the results obtained are returned to the respective prefectures. The present Topic summarizes the incidence of the two diseases based on the isolation reports and the information obtained from laboratory findings on the isolates during January 1994 through September 1996.
Cases of typhoid fever (the sum of patients and carriers) numbered 74 and 61 in 1994 and 1995, respectively, showing a tendency of continuous decrease except for 1993 (Table 1). Cases of paratyphoid fever, on the other hand, numbered 51 in 1994 owing to the winter outbreak having occurred from December 1993 to January 1994 and 71 in 1995 owing to the one during August to September in this year (Fig. 1). Cases of paratyphoid fever outnumbered those of typhoid fever for the first time in this country (Table 1). The proportion of imported cases has been high with respect to either disease.
The outbreak due to both PT1 and PT2 of S.Paratyphi A having occurred in the winter of 1993-1994 in the Shima area, Mie Prefecture, mentioned in a previous Topic (see IASR, Vol. 15, No. 4), was interpreted from the subsequent examinations of food and the environment and epidemiological investigation that contamination of the fishing port with S.Paratyphi A occurred for some reason or other and the organisms were uptaken by live oysters and other fish and shellfish, which served as the source of infection of consumers (reported at the 17th Annual Meeting of the Association of Public Health Laboratories for Microbiological Technology, 1996).
During July-November 1995, cases of paratyphoid fever due to S.Paratyphi A PT3 were found in a wide area; there were 24 patients in all, one in July, 16 in August, six in September and one in November. These patients were found in 14 prefectures. A wide-area outbreak was suggested in the light of the occurrence during such a short period, the rare cases of paratyphoid fever due to PT3 in this country, counting only three during the five years from 1990 to 1994, and the identical DNA patterns of the isolates found by pulsed-field gel electrophoresis. The source of infection , however, was not identified (see IASR, Vol. 16, No. 10).
In March 1996, S.Typhi (PTD2 and M1) and S.Paratyphi A (PT1) infections occurred among 17 university students and their leaders who visited Singapore, Malaysia and Indonesia. Several students were having such symptoms as mild diarrhea, but the results of the bacteriological examination given at the airport quarantine station turned out to be negative. Later, eight of them developed such symptoms as fever, the medical examinations detected either organism, and the patients were admitted to isolation facilities. Mixed infections with Shigella, Salmonella, or Giardia lamblia were found in three of them (see IASR, Vol. 17, No. 7).
Table 2 shows distribution of S.Typhi PTs and Table 3 that of S.Paratyphi A PTs. S.Typhi isolated during 1994-1996 included 24 PTs, of which domestic isolates involved 15 and the imported ones 21 types. PTs D2, A, M1, E1, UVS1, B1 and DVS were frequently found among both domestic and imported isolates, but the frequencies changed slightly year after year. PTUVS1 found in 12 and seven isolates in 1994 and 1995, respectively, decreased to only two in 1996. On the contrary, PTA, found in only six and four isolates in 1994 and 1995, respectively, increased to 14 in 1996. S.Paratyphi A involved five PTs; only two of them were found in 1996 and the majority of the isolates were of PT1.
In Fig. 2, shown are the age distribution of typhoid and paratyphoid fever cases. As usual, there were many cases of either disease in the age group of 20-29 years. The mean period of time required from onset of illness to laboratory-confirmed diagnosis were 13.3 days for typhoid fever and 14.7 days for paratyphoid fever during 1994-1996, being close to those in previous years. There were eight (4.2%) and 13 (9.0%) cases of typhoid and paratyphoid fever, respectively, which required longer than 6 weeks before laboratory-confirmed diagnosis.
Isolation of drug-resistant S.Typhi is shown in Table 4. S.Typhi resistant to five antibiotics was isolated from returnees from Indian Subcontinent, Cambodia, Vietnam and so on, indicating that the prevalence of this organism is being kept on in these areas. Eight, including two domestic isolates, of 22 S.Paratyphi A PT1 isolates in 1996 were resistant to sulfamethoxazole-trimethoprim (see p. 298 of this issue).