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HEALTH
sampling of night-soil and, in special instances, of sea water, well water and foodstuffs liable to be sources of transmission of cholera vibrios. In addition, a mass immunization campaign against cholera was carried out which began in May, as a result of which 1,708,764 persons, representing 48 per cent of the population, had been immunized with doses of standard vaccine of 8,000 million organisms per millilitre when the first case of cholera was confirmed on 29th June. Quarantine restrictions were maintained in respect of the Philippines and Kwangtung Province in South China, and were applied to Indonesia, Malaya, Burma and South Korea when these countries were declared infected.
The first positive laboratory finding in Hong Kong during 1963 was from a case of suspected cholera admitted to the Sai Ying Pun Hospital on 27th June. This was not an imported case and no contact with individuals coming recently from infected areas could be traced. The whole Colony was declared an infected local area on 29th June when laboratory confirmation was received. Vibrio cholera El Tor was isolated, the strain being in all respects similar to those occurring in the 1961 and 1962 outbreaks. Between 29th June and 21st December there were 115 cases of cholera, all of which were confirmed bacteriologically. Forty per cent of these were not typical, the disease being very mild. There were six deaths, four directly due to the disease and a further two due to intercurrent causes.
Initially the outbreak appeared to be similar to that experienced in the previous two years, except for its earlier onset, its late con- tinuation and the high proportion of mild cases. The first case on 27th June was earlier than expected and a total of 27 cases had been reported by 19th September. There was then a break until 28th September, when, instead of the incidence declining as had been the case in 1961 and 1962, an additional 88 cases were reported during the last quarter of the year-a period which in previous experience had always been almost completely free from the disease. Almost all contacts of the 115 cases were isolated at the Chatham Road Quarantine Centre, and among 2,310 con- tacts accommodated at the centre 119 contact carriers were detected.
The usual environmental measures were applied, including in- creased chlorination of the public water supply, chlorination of all wells in the urban areas and vigorous inspection of public