The Topic of This Month Vol.21 No.2(No.240)
Adenoviruses comprise 49 serotypes classified into six groups, from A to F, based on their biological characteristics, tumorigenicity, and DNA homology. Adenovirus infection provokes a variety of clinical symptoms. Upper respiratory tract inflammation, keratoconjunctivitis and gastroenteritis are the three major symptoms, but the symptoms provoked differ from one group to another. Group A has a high tumorigenicity, which differentiates it from the other groups, and its detection has seldom been reported by the Infectious Agent Surveillance under the National Epidemiological Surveillance of Infectious Diseases (NESID). Groups B and E are detected mainly from cases of upper respiratory tract inflammation and keratoconjunctivitis, group C from those of upper respiratory tract inflammation, group D from those of keratoconjunctivitis, and group F from those of gastroenteritis. The following is a summary of the recent trend of adenoviruses isolated by cultivation or detected by other methods (hereafter referred to as detected) by prefectural and municipal public health institutes (PHIs).
The serotypes of adenoviruses detected during 1991-1999 are shown by year in Table 1 (for the information before 1990, see IASR, Vol. 16, No. 5). During the five years from 1995 through 1999, the reports of detection totaled at 10,010 (as of January 26, 2000). They include 17 serotypes of 1 to 41, type 34/35, an intermediate between types 34 and 35, and type 40/41, indistinguishable between types 40 and 41 with a commercial ELISA kit. Most frequently detected were viruses of type 3, followed by types 2, 1, 7, 5, 19, 8, 6, 40/41, 4, 37, and 11 in this order. The other types were seldom detected. The number of reports of type 3 detection in 1998 (1,421) exceeds that in 1987 (932) which was the largest of those before 1997. Adenovirus type 4, causing epidemic keratoconjunctivitis (EKC) and pharyngoconjunctival fever (PCF), was in the increase during 1991-1992 but since 1993 has rarely been detected. Type 31, which rarely used to be reported, was detected from cases of gastroenteritis and so was type 35 from cases of hemorrhagic cystitis (see IASR, Vol. 18, No. 2 and Vol. 19, No.2).
Adenoviruses are detected mostly from nasopharyngeal specimens of cases of upper respiratory tract inflammation, eye swabs of those of keratoconjunctivitis, and stool specimens of those of gastroenteritis, reflecting the main symptoms emerged (see IASR, Vol. 15, No. 5). If the frequencies of detection from the three different specimens were to be compared in the yearly reports of detection during 1995-1999 (Table 1), it will be obvious that groups B and C were detected mainly from nasopharyngeal specimens, group D mostly from eye swabs, and group F all from stool specimens. An exception is type 11 of group B, which is an etiological agent of hemorrhagic cystitis, often detected from urine samples, and rarely detected from such specimens as listed in the table.
The trend of monthly detection of representative serotypes by group is shown in Fig. 1. Detection of type 3 of group B, being an agent of PCF, increased largely forming a peak in July 1998. Type 7 of group B, re-emerging in Japan in 1995 (see IASR, Vol. 17, No. 5 & Vol. 18, No. 4), raised the attention of medical field as its detection increased during 1996-1998 accompanying serious cases and even fatal pneumonia ones (see IASR, Vol. 19, No. 7). Its detection, however, decreased in 1999. Furthermore, detection of type 7 formed peaks during June and July of 1997 and 1998, when it was frequent. Types 1, 2 and 5 of group C are detected constantly every year, but do not show any distinct seasonal trend; neither does group D. However, detection of group D increased widely from summer toward autumn. Types 8 and 37 were frequently isolated during 1995-the first half of 1996, and so were type 19 during the second half of 1996-1998. It can be seen that the serotypes of adenoviruses causing keratoconjunctivitis have changed since July 1996. Detection of group F increased during November and December of 1997 and 1999, when it was slightly more frequent.
The trend of PCF cases per sentinel for pediatric disease clinic (including reports from sentinel eye disease clinics until the 13th week of 1999) and that of EKC cases per sentinel eye disease clinic reported during 1995-1999 are shown in Fig. 2. The incidence of PCF shows a peak increase in summer of every year (see IASR, Vol. 16, No. 5 for 1990-1994), which is linked with the trend of detection of group B during the last 5 years shown in Fig. 1. In 1998, cases increased, probably reflecting the epidemics of type 3 infection from the above-described data of agent detection. Cases of EKC occur all year round, forming a wide peak in the third quarter of the year, and shift in a pattern similar to that of detection of group D as seen in Fig. 1.
Of the main symptoms of adenovirus infection, upper respiratory tract inflammation and gastroenteritis are seen mainly among children, and keratoconjunctivitis among adults (see IASR, Vol. 15, No. 5 & Vol. 16, No. 5). Figure three shows the age distribution patterns of cases from which the representative types of four major groups, viz. type 3 of group B, type 2 of group C, type 19 of group D, and type 40/41 of group F, were detected during 1995-1999. Types 3, 2, and 40/41 were detected from children with peaks at the ages of 4, 1, and 0, respectively, while type 19 was detected mostly from adults. Type 3 was also detected frequently from adult conjunctivitis cases, forming another small peak at the age of 30s.