Jpn. J. Infect. Dis., 58, 2005

Laboratory and Epidemiology Communications

Comparison of the Incidence of Norovirus Infection in Homes for the Elderly
Mika Akizuki1*, Kazue Nakagawa2, Tatsuya Kato3, Tsuyoshi Ogata1,4 and Yoshikazu Nakamura5
1

Ibaraki Prefecture Itako Public Health Center, Ibaraki 311-2422,
Ibaraki Prefecture Tsuchiura Public Health Center, Ibaraki 300-0812,
3
Ibaraki Prefecture Ryugasaki Public Health Center, Ibaraki 301-0822,
4
Ibaraki Prefecture Tsukuba Public Health Center, Ibaraki 305-0035 and5
Department of Public Health, Jichi Medical School, Tochigi 329-0498, Japan2

Communicated by Tatsuo Miyamura(Accepted August 11, 2005)
40

In Japan, outbreaks of norovirus infections in homes forthe elderly are increasing. According to a nation-wide survey
conduced by the Ministry of Health, Labour and Welfare,
5,371 cases of gastroenteritis and 12 deaths due to norovirus
infection were reported between November 2004 and January 2005, indicating the importance of caution in norovirus
infection in the elderly who are relatively less resistant toinfectious diseases. Between January 5th, 2004 and January
24th, 2005, norovirus infections occurred at four homes forthe elderly in the southern area of Ibaraki Prefecture. In allof these cases, norovirus was detected in fecal samples ofpatients by reverse transcription (RT)-PCR.
In the present study, we investigated the incidence of
norovirus infection in the elderly by age using Mann-Whitney’s
statistical U-test (software Dr. SPSSII, SPSS Japan Inc.,Tokyo, Japan). Only patients with diarrhea or vomiting wereincluded. Of 327 patients, 115 were aged between 50 - 79years, 146 between 80 - 89 years, and 66 patients 90 years ormore. The numbers of patients with diarrhea or vomiting,and the incidence are shown in Table 1. As shown in Figure
1 and Table 2, patients aged more than 90 years had asignificantly higher incidence of vomiting (P < 0.05) whencompared with those aged less than 90 years, while no difference was observed in the incidence of diarrhea among theseage groups.

3530Rate (%)

25Diarrhea
Vomiting

2015105050- 79

80- 899 0 - o v erAgeFig. 1. Incidence of symptoms by age.

Table 2. Results of the Mann-Whitney’s U-test
SymptomComparison with each age

Probability of significanceDiarrhea

50 - 79 and 80 - 89
50 - 79 and 90 - over
80 - 89 and 90 - over

0.978
0.118
0.096

Vomiting

50 - 79 and 80 - 89
50 - 79 and 90 - over
80 - 89 and 90 - over

0.897
0.047
0.049

Table 1. Age comparison in homes for the elderly and their symptoms
Age

Diarrhea
Vomiting

50 - 79(n = 115)
No. Rate1)

80 - 89(n= 146)
No. Rate

90 - over(n = 66)
No. Rate

Total(n = 327)
No. Rate

2326293420247284

20.0
22.6

19.923.3

30.3
36.4

The present results indicate that the incidence of norovirus
infections in people aged more than 90 years is high in homes
for the elderly, and that special attention should be paid tothis issue in order to reduce transmission.

22.0
25.7

This article appeared in the Infectious Agents Surveillance
Report, vol. 26, no. 5, p. 11-12 (in Japanese).

1): Incidence (%) of people in homes for the elderly.

*Corresponding author: Mailing address: Ibaraki Prefecture Itako
Public Health Center, Osu 1446-1, Itako, Ibaraki 311-2422,Japan. Tel: +81-299-66-2114, Fax: +81-299-66-1613, E-mail:m.akizuki@pref.ibaraki.lg.jp326