THE 7TH PANDEMIC OF CHOLERA IN THE USSR, 1961-89

Over the period 1961-89 a total of 1713 057 cases of cholera were repo rted to WHO from 117 countries in all continents. The course of the ep idemic fell into three periods: in period I (1961 to 1969), 24 countri es (predominantly in Asia) reported about 419 968 cholera cases; in pe riod II (1970 to 1977), 73 countries from Asia, Africa, Europe, and th e Americas reported 706261 cases; and in period III (1978 to 1989), 83 countries reported 586 828 cases. The global epidemic was at its most severe in 1967-74. Subsequently morbidity declined and up to 1989 had remained high and stable, with 44 000-52 000 cases per annum. In the USSR 10 723 cholera cases and carriers were reported between 1965 and 1989 from 11 republics (but not Latvia, Lithuania, Estonia, or Armenia ). In 1965 and 1970-74 large-scale outbreaks of imported cholera were characteristic of the epidemic in the USSR. Thereafter morbidity decli ned, and sporadic cases were reported along with environmental, predom inantly nontoxigenic strains of cholera vibrio. Most of the outbreaks in the 1970s were waterborne, and virulent strains containing the vct- gene were isolated from samples of water. Large-scale outbreaks contin ued that were associated with seafood and dairy produce that were cont aminated with cholera vibrio. Clinical cases of cholera as well as a c onsiderable number of carriers of avirulent nontoxigenic strains were reported. The epidemiological situation in the USSR is unstable, with cases of cholera and virulent strains from surface water being reporte d every year. Cholera control measures in the USSR have been modified considerably over the period of the pandemic, resulting in a reduction in the socioeconomic costs of preventive and anti-epidemic measures. The USSR has been regionalized into three epidemic types based on the risk of outbreaks and spread of cholera, intensity of migration, and t he type and severity of epidemic. Also the control and preventive meas ures have been differentiated, taking into account the virulence (vct- gene) of cholera vibrio strains isolated from cholera patients and car riers.