STUDIES ON RUBELLA: 1. EPIDEMIOLOGICAL PATTERN AND SEROEPIDEMIOLOGY OF A RUBELLA OUTBREAK IN TOYAMA PREFECTURE IN 1967

An epidemic of rubella occurred in Toyama Prefecture in early spring in 1967. A prefecturewide hospital surveilance indicated that the epidemic was mainly localized in the south-westernpart of the prefecture, with Fukumitsu town as its center, that the peak age of the patients was 6 to 7, and that 18 of 22 patients over 20 years of age were female. Fever, whole body skin eruption, and swelling of the cervical lymph node appeared in 72.1%, 68.9%, and 41.6%, respectively, of the patients. Virological and seroepidemiological studies gave the following results. 1. Six strains of rubella virus were isolated from the throat swab and or blood of 5 patients consisting of 1 primary schoolchild, 3 junior-high-school boys, and 1 adult. 2. In patients with clinical manifestations, HI antibody response to rubella virus was rapid. The titer being 1:512 only 4 days after the onset of the disease. 3. After the epidemic, the antibody level was still very low (between ×8 and ×256) among nursery schoolchildren. It became higher with the advance in age. More than a half of the adults examined showed an intermediate antibody level (between ×8 and ×256). 4. Before the epidemic, 2 distinct patterns were observed in different districts with regard to the antibody level in various age groups. On antibody was detected from 2 age groups, 10 to 11 and 2 to 3. 5. The antibody level in adults after the epidemic was much higher than that before the outbreak. 6. Adults whose family member was infected with rubella virus showed a significantly higher peak in the distribution of antibody titers than those whose family member had not been infected with the virus. This may indicate the possibility that adults possessing a relatively low antibody level may have been reinfected with the virus or at least got a booster response to the virus.