The Topic of This Month Vol.17 No.9 (No.199)
Herpangina is an acute febrile disease characterized by vesicles developing from the pharynx to the soft palate and prevails in summer every year among infants mostly under 4 years of age, particularly those aged one year. It is caused chiefly by group A coxsackieviruses (CA). This topic deals with the incidence of herpangina in 1996 and the virus isolation in 1995 referring to the provisional reports on that in 1996.
The weekly herpangina cases reported by the National Epidemiological Surveillance of Infectious Diseases (NESID) in 1996 started to increase from the end of May as was the case in 1995 and reached the largest number (4.65 cases per sentinel clinic) during the 28th week (July 7-13) (Fig. 1). The cases reported up to the 33rd week (August 11-17) of 1996 numbered 84,912 (35.20 cases per sentinel clinic), already surpassing 79,573 cases reported for the year of 1995 (32.61 cases per sentinel clinic). On the other hand, those reported till the same period in Hokkaido (17.63 cases per sentinel clinic) were far less than those for the year of 1995.
The incidence during the 26th, 28th and 30th weeks in 1996 in each prefecture is shown in Fig. 2. As usual, the epidemics have shifted from the west toward the east part of Japan.
The etiological agents will be mentioned on the basis of the information on virus isolation reported in IASR. The trend of weekly CA virus isolation from herpangina cases during January 1995 through July 1996 is shown in Fig. 3. In 1995, CA4 was isolated most frequently and CA6 and CA5 followed. The largest number of reports on isolation of CA4 came during the 26th week (June 25-July 1). Since it takes a long time to isolate and identify viruses, the results of the surveillance in 1996 have been reported only from western Japan where the epidemic occurred earlier. Reports have increased in number since the 16th week (April 14-20) on isolation of CA4 for the most part as was the case in 1995. Isolation of CA6 and CA10 have also been reported less frequently.
The reports on isolation of CA4 in 1995 numbered 201, of which 153 were from herpangina cases. Isolation was accomplished at 22 public health institutes (PHIs) in Shimane, Kanagawa, Nagano and other prefectures. Those of CA6 numbered 72 (58 were from herpangina cases), coming from 14 PHIs in Akita, Nagano and other prefectures. Those of CA5 numbered 55 (39 were from herpangina cases) from 15 PHIs.
Up to the 28th week of 1996, reports on isolation of CA4 numbered 58 (46 were from herpangina cases) from seven PHIs in western Japan, including 46 reports from Oita PHI. Those of CA6 numbered 42 (16 were from herpangina cases) from six PHIs, including 28 reports from Shimane PHI; those of CA10 numbered 18 (13 were from herpangina cases) from five PHIs, including 10 reports from Nara PHI (as of August 22, 1996).
To elucidate the trend of major serotypes causing herpangina, CA viruses isolated from herpangina cases since the start of NESID have been summarized (Table 1). During the 14 years from 1982 through 1995, principally five serotypes, CA2, 4, 5, 6, and 10, were isolated. CA3 was isolated frequently only in 1982. The serotype most frequently reported during the 14 years' period was CA4 (1,712 reports), followed by CA10 (1,218 reports). Of the reports on isolation of CA4 and CA10, 70% and 64%, respectively, were from herpangina cases. Isolation of CA10 increased markedly in 1984, and increase and decrease have altered every other years after 1988, while CA4 has been isolated constantly every year.