The Topic of This Month Vol.17 No.5 (No.195)

Reports on isolation of adenovirus type 7 (Ad7), which used to be very few before 1994, have increased since 1995,coming in successively from the whole country.

Ad7,like type 3 (Ad3),is a subgenus B adenovirus and multiplies in various organs such as the conjunctiva, pharynx,lungs,and intestines, eliciting varieties of symptoms. Particularly, it may elicit lethal respiratory diseases in children with a basal ailment in the heart or lung (CDC, MMWR, Vol.32, No.19,1983). In England and Wales,isolation of Ad7 used to be very rare before 1971, but started to increase in 1972. An extensive outbreak occurred in 1973-74 and thereafter smaller outbreaks occurred every 3 or 4 years (CDSC, CDR, 84/23, 1984).

In this topic, reports on isolation of Ad7 cited in IASR will be summarized and clinical symptoms and age distribution of patients of Ad7 infection compared with those caused by Ad3, a closely related virus.

Many adenoviruses are reported every year in Japan and Ad3 accounts for about one-third of such reports (see IASR, Vol. 15, No. 5). During the 14 years from 1980 through 1993, reports on isolation of Ad3 numbered 7,187, in contrast to only 30 reports of Ad7 including 12 from Aichi PHI in 1992 (Table 1) (see IASR, Vol. 16, No. 1).

There was no report on isolation of Ad7 in 1994, but it was isolated in Hiroshima City in May 1995 (see IASR,Vol.16,No.11). In June, an outbreak of influenza-like illness with high fever occurring in a dormitory was reported for the first time from Yamanashi Prefecture (of 202 boarders,145 became ill and 31 of them were hospitalized) (see p. 101 of this issue). After July 1995, isolation of Ad7 has been reported every month; so far,there have been 90 reports from 10 laboratories (Table 2; as of April 23, 1996).

Of 90 patients from which Ad7 was isolated, 76 were with clinical diagnoses reported; respiratory illness for 64 patients (84%) (influenza- like illness for 24,common cold 20, pharyngoconjunctival fever nine, bronchitis five,pneumonia four,atypical pneumonia one, and herpangina one). The others were epidemic keratoconjunctivitis for four patients, conjunctivitis two,infectious gastroenteritis four,intussusception one, and myositis one.

The clinical symptoms of 86 of the 90 patients from which Ad7 was isolated and of 379 patients from which Ad3 was isolated during the same period are listed in Table 3. In Ad7-isolated patients, fever was seen in 87%, upper respiratory-tract illness in 69%, and lower respiratory-tract illness in 14%,the ratios being similar in Ad3-isolated patients. Maximum body temperatures were compared (Fig. 1). A larger number of Ad7-isolated patients showed body temperatures higher than 40C, accounting for 38% of all patients, as compared with 25% of Ad3-isolated patients.

The age distributions were compared between the Ad7- and Ad3-isolated patients. They were grouped into four from clinical diagnosis or symptoms reported; group 1 comprised those with lower respiratory-tract illness, group 2 those without lower respiratory-tract illness but with upper respiratory-tract illness, group 3 those without upper nor lower respiratory-tract illness but with conjunctivitis, and group 4 those with gastroenteritis only (Fig. 2). Ad7-isolated patients belonging to the lower respiratory-tract illness group were under 5 years of age; the same tendency was seen with Ad3-isolated patients. Ad7-isolated patients of the conjunctivitis group were above 10 years of age, including adults of different ages as were Ad3-isolated patients (see p. 102 of this issue). The Ad3-isolated patients belonging to the upper respiratory-tract illness group are distributed in a unimodal curve with a peak at 4 years of age, whereas the Ad7-isolated patients including those in an outbreak occurring in Yamanashi Prefecture (11 patients of 15-24 years of age) were distributed in a bimodal curve.

The specimens from which Ad7 was isolated included 64 nasopharyngeal swabs,13 nasopharyngeal swabs+stool specimens, nine eye swabs, two stool specimens,one nasopharyngeal swab+eye swab, and one nasopharyngeal swab+stool specimen+urine specimen.

Adenovirus is excreted into the stools for a long period, during which it may be transmitted to other persons. For rapid diagnosis, it is possible to detect directly the adenovirus antigen in stool specimens and pharyngeal swabs by using a commercial ELISA kit (according to Hiroshima City PHI). The antisera for type identification of adenovirus isolates are being marketed by Denka Seiken Co.

Editorial Note: Attention having been paid to the trend of Ad7 since its isolation in May 1995, a report on isolation of Ad7 from two dead infantile cases was furnished by a hospital in Chiba Prefecture in March 1996 (isolation and identification were undertaken by a commercial diagnostic laboratory). The Infectious Diseases Control Division of the Ministry of Health and Welfare sent out a written warning against Ad7 to every prefecture and designated city on April 8, 1996.

Disinfection of adenoviruses:the virus is inactivated with sodium hypochlorite, but resistant to cationic detergents. Disinfection is more effective with 90% rather than 70% ethanol. Isopropanol is ineffective.

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