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In 1996, Vibrio cholerae O1 biotype E1 Tor continued to occur in all regions of the world (Map 1). The decrease in the number of cases observed since 1994 continued in 1996, with a total of 143 349 cases and 6689 deaths officially reported to WHO. The decrease in the number of cases is not reflected in the global case-fatality rate (CFR), which increased to 4.7% compared with 2.4% in 1995. The number of countries reporting cholera to WHO decreased from 78 in 1995 to 71 in 1996 (Table 1 and Figs. 1-3). Africa is the continent accounting for the largest proportion of all reported cholera cases. The incidence of cholera increased by 53%, from 71081 cases in 1995 to 108535 cases in 1996. The CFR in Africa reached 5.7%, representing the highest figure in all the regions. The Americas reported an important decrease in the number of cases, from 85 809 in 1995 to 24643 in 1996, i.e. 71%. In Asia, 10 142 cases were reported in 1996, but a few countries which reported high incidence rates in 1995 have not yet sent their final report to WHO. It is estimated that a decrease of about 30% will be observed in Asia once final reports have been received.

Cholera is an acute dehydrating diarrhoeal disease, traditionally caused by vibrio cholerae O1, and also more recently by V. cholerae O139 (Bengal). Traditionally, water was recognized as the primary vehicle for transmission of cholera, but in the past 30 years, outbreaks of cholera associated with eating contaminated food have demonstrated that food also plays an important role, although in many instances water is the source of contamination of foods. Most commonly associated with cholera is seafood, both molluscan shellfish and crustaceans. Seafood may be contaminated in its natural environment or during preparation. Other food items associated with outbreaks are fruit and vegetables, meat, cooked grains, etc. Vegetables are usually contaminated by contact with sewage in soil and fruits when injected with contaminated water to increase weight and turgor. Food items initially free from V. cholerae organism may become contaminated when mixed with water, or other contaminated food, or through handling by infected persons who have not observed proper hygiene. Refrigeration, freezing, alkaline pH, high concentration of carbohydrate, humidity and absence of competing flora enhance the survival of V. cholerae in food. Survival of V. cholerae is shorter in food with acidic pH. Foodborne cholera can be averted by the hygienic preparation of food and its consumption. However, since the vehicles of transmission vary markedly from place to place, being affected by local customs and practices, selected control and preventive measures that are most important locally must be implemented. To this end, application of the Hazard Analysis and Critical Control Point system to food preparation is essential in order to identify the practices which may present a risk. Restrictions on importation of foods which do not present a risk of being contaminated from areas where cholera is endemic is not warranted.

In 1994, Vibrio cholerae O1 biotype El Tor, the agent responsible for the seventh cholera pandemic which began in 1961, continued to spread in all regions of the world (Map 1). In all, 384,403 cholera cases were officially reported to WHO in 1994 (a 2% increase over 1993), reversing the downward trend which started in 1992. A total of 10,692 deaths were reported in 1994, increasing the reported global case-fatality ratio (CFR) to 2.8% from 1.8% in 1993. Cholera cases were notified from 94 countries/areas, the highest number ever reporting in one year. (Table 1 and Fig. 1). The year was marked by the dramatic cholera outbreak that devastated the Rwandan refugee camps in Goma, Zaire in July. Major outbreaks also affected Afghanistan, Brazil, Guinea, Guinea-Bissau and Somalia. Africa reported a rise in the number of cholera cases, and was the continent accounting for the largest proportion of all reported cases. The incidence of cholera cases in the Americas continued to fall and reported CFR was the lowest recorded since the disease reached Latin America in 1991. Asia reported a 17% increase in cholera cases compared with 1993. Europe, which usually reports only imported cases, registered a significant increase in the number of indigenous cholera cases. Oceania reported 6 cases, 5 of which were imported, and no deaths (Figs. 2 and 3). The new V. cholerae strain O139 (Bengal) has affected 10 countries in Asia since it was first detected in India at

In 1993, the seventh pandemic of Vibrio cholerae O1 biotype El Tor, which began in Indonesia in 1961 and reached South and Central America in 1991, continued in all regions of the world (Map 1): a total of 376,845 cases and 6,781 deaths were reported from 78 countries, with a global case-fatality ratio (CFR) of 1.8%. This represents an 18% reduction in the number of reported cases and a 16% reduction in the number of reported deaths compared with 1992. The number of countries reporting cholera is the highest ever recorded in any one year (Table 1, and Fig. 1). A total of 209,192 cases and 2,438 deaths were reported from the Americas, a 41% reduction in the number of cases and a 1.5% increase in the number of deaths from 1992. Africa reported 76,713 cases and 2,532 deaths, a 16% reduction in the number of cases and a 52% reduction in the number of deaths from 1992. Asia reported 90,862 cases and 1,809 deaths, a five-and-a-half-fold increase in both the number of cases and deaths (Figs. 2 and 3). Europe reported 73 cases (the majority imported) and 2 deaths, a four-fold increase in the number of cases. Five imported cases were reported by Australia in the Oceania region. Of particular importance during 1993 was the emergence of epidemic cholera produced by a non-O1 cholera serogroup. V. Cholerae O139 (Bengal) was first identified in 1992 as the causative organism of large outbreaks in India and in 1993 was isolated in 7 countries in Asia. Imported cases have been reported from 5 other countries.(ABSTRACT TRUNCATED AT 250 WORDS)

Reported are the results of an unmatched case-control study to determine the risk factors associated with acquisition of cholera in Manila. Cases were patients admitted to the San Lazaro Hospital between July and September 1989 and whose stools yielded Vibrio cholerae O1 on culture. Controls were patients admitted to the same hospital and who had no history of diarrhoea or of having taken antibiotics during the 3 days prior to admission. Of the 158 cases and 158 controls who had bought food from street vendors, cases were more likely to have bought the following items: pansit (rice noodles with shrimp, meat, and vegetables), mussel soup, spaghetti, fish balls, pig blood coagulated with vinegar, and salty brine shrimp with vegetables. Cases were also more likely to lack piped water at home. An unconditional logistic regression analysis indicated that only pansit (OR = 2.15, 95% CI = 1.32-3.51), mussel soup (OR = 2.29, 95% CI = 1.06-4.95), and the absence of piped water at home (OR = 2.70, 95% CI = 1.63-4.46) remained as risk factors. As control measures we recommend stricter implementation of the food sanitation code and the licensing of street food vendors.

Over the period 1961-89 a total of 1,713,057 cases of cholera were reported to WHO from 117 countries in all continents. The course of the epidemic fell into three periods: in period I (1961 to 1969), 24 countries (predominantly in Asia) reported about 419,968 cholera cases; in period II (1970 to 1977), 73 countries from Asia, Africa, Europe, and the Americas reported 706,261 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 declined, and sporadic cases were reported along with environmental, predominantly 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 continued that were associated with seafood and dairy produce that were contaminated with cholera vibrio. Clinical cases of cholera as well as a considerable 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 reported every year.(ABSTRACT TRUNCATED AT 250 WORDS)

The cholera epidemics of the XIXth century are described and reviewed. The extent, incidence and case-fatality rate for the disease in the seventh pandemic are described. The global epidemiological situation and its trend at the end of 1991 are analysed. A review of cholera epidemiology highlights the factors that might explain the less tragic nature of the disease today. The role of water, food and direct contagion in transmission of cholera over the last 20 years is considered in the light of recent studies and with special reference to the epidemic in Latin America, where the intense emotion aroused by the disease has prompted vigorous action that could produce significant and lasting progress in the health field.

Vibrio cholerae O1 is an important cause of diarrhoeal disease in large parts of Asia and Africa. The seventh pandemic of cholera is still continuing (92 countries have so far been affected), and other organisms related to V. cholerae O1 are being reported increasingly frequently as the cause of diarrhoeal outbreaks as well as endemic diarrhoea.Recent research has considerably increased our understanding of how cholera is transmitted, the mechanisms by which V. cholera O1 produces disease, and the functioning of the local intestinal immune response by which individuals can be protected from infection. One result of these advances has been the development of experimental cholera vaccines, derived from non-living and attenuated live strains, which promise to become a new tool for the control of cholera. These matters, which were reviewed by the WHO Scientific Working Group on Bacterial Enteric Infections at a meeting in Geneva, Switzerland, in September 1984, are described together with recommendations for future research.

In order to define the role of water used for drinking, cooking, bathing, and washing in the transmission of Vibrio cholerae biotype eltor infections in an area with endemic cholera, surveillance was initiated in neighbourhoods with a culture-confirmed cholera index case and others with index cases with non-cholera diarrhoea as controls. In neighbourhoods with cholera infection, 44% of surface water sources were positive for V. cholerae, whereas only 2% of surface sources were positive in control neighbourhoods. Canals, rivers, and tanks were most frequently positive. There was an increased risk of infection for families using water from culture-positive sources for drinking, cooking, bathing, or washing and for those using water sources used by index families for drinking, cooking or bathing. Analysis of the results for individuals showed that in this case there was an increased risk of infection associated with using water from culture-positive sources for cooking, bathing, or washing, but not with using water from culture-positive sources for drinking. Individuals who used the same water source as an index family for bathing were more likely to be infected than those using different sources. For families drinking from a culture-negative source, there was an association between infection and bathing in a positive source. For families using a different bathing source from the index family there was an association between infection and drinking from the same source as the index family, and for families using a different drinking source from the index family there was an association between infection and bathing in the same source as the index family. These data suggest that use of surface water is important in the transmission of V. cholerae and that, in addition to providing safe drinking water, education regarding the risk of transmission of infection by water from potentially contaminated sources used for other purposes, especially bathing, may also be necessary to control transmission in areas where eltor cholera is endemic.

Doxycycline was used among the family contacts of hospitalized cholera patients in Calcutta to determine its effectiveness in controlling transmission of V. cholerae infection. A total of 137 such contacts were given a single oral dose of doxycycline in graded doses according to age. A similar group of 139 contacts received a single dose of multivitamins as placebo. All 276 contacts were examined bacteriologically daily for 10 days for the presence of V. cholerae in their stools. The results showed that doxycycline was effective in significantly reducing the load of V. cholerae infection for up to 5 days following treatment.

In the period 10 August 1978-23 January 1979, 913 culture-confirmed cases of cholera caused by Vibrio cholerae, biotype El Tor, serotype Ogawa, occurred in Bahrain. After discovery of the initial cases, others occurred sporadically, and the incidence reached a peak of 25-35 cases per day during the seventh week of the outbreak (16-22 September). The overall attack rate (27 per 10 000) was low and the outbreak subsided without mass immunization campaigns or rigorous border control of persons and imports. Investigation of 746 culture-confirmed cases that occurred in the period 10 August-13 October 1978, showed that cases occurred throughout most areas of the country and mainly affected infants, young children, and adult working-age males. Symptoms were very mild; fewer than 20% of patients required specific rehydration therapy. The highest attack rate (84 per 10 000) occurred in infants less than 1 year of age. No common vehicle or mode of transmission was identified. A matched-pair study of 35 cases and controls showed that adult cases were more likely than controls to have consumed food or beverage outside of the home before becoming ill. V. cholerae was isolated from stored drinking water in the houses of 8 cases but not from numerous samples of food and tap-water. It was presumed that cholera transmission occurred through a complex interaction of mild and asymptomatically infected persons with food, water, and the environment.

Sulfadoxine, a long-acting sulfonamide, and tetracycline were compared as regards their effectiveness in reducing transmission of cholera infection among the contacts of cholera patients in Calcutta. A total of 109 healthy family contacts of confirmed hospitalized cholera patients were treated with a single oral dose of sulfadoxine graded according to age. Another similar group of 101 contacts received 6 divided doses of oral tetracycline over a period of 3 days. All these contacts were bacteriologically examined for 15 days. Results showed that tetracycline was effective in significantly reducing the load of cholera infection from the 2nd to 6th day, while sulfadoxine was effective from the 3rd to the 6th day. The advantages and disadvantages of the two drugs as chemoprophylactic agents in cholera are discussed.

The apparent failure of handpump tubewells to reduce the incidence of cholera among users in the flooded rural area of Bangladesh has stimulated interest in defining precisely the means of Vibrio cholerae transmission during localized outbreaks. Cholera-infected neighbourhoods were placed under intensive microbiological surveillance to pinpoint contaminated sources and subsequent infections. The results show that cholera transmission was via contaminated surface water, particularly water taken into households for cooking or drinking. Infections resulted from a daily dose not exceeding 10(5) organisms and the frequency of exposure appeared to be a major determinant of the infection rate. The importance of these data in environmental interventions and particularly in the provision of tubewells is discussed.

Transmission of eltor cholera infection in endemic communities continues without diminishing because of the absence of effective intervention measures. Two methods-chlorination of stored water and the use of a narrow-necked earthenware vessel (called a 'sorai') for storing the water-were found to be effective in reducing the transmission of infection among the family contacts of cholera patients. The cholera carrier rates in the chlorination and 'sorai' intervention groups were 7.3% and 4.4%, respectively, compared with 17.3% in the control group. The 'sorai' is cheap and was well accepted by the local communities; its narrow neck prevented the introduction of the hand and contamination of the stored water.