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the 30th September, there was a total of ten clinical cases of cholera, nine of which were confirmed bacteriologically. All cases were typical and the majority were severely ill. There was one death, the third patient, who died on arrival at the hospital after an illness lasting three days.

81. All house contacts of the ten clinical cases were isolated at the Chatham Road Quarantine Centre and, amongst the total of 126 con- tacts accommodated at the Centre, only 4 contact carriers were detected. These were all contacts of the first case.

82. The usual environmental preventive measures were applied, such as increased chlorination of the public water supply, the chlorination of all wells in the urban areas and the vigorous inspection of public cating places, food premises, markets and the control of itinerant food hawkers. Particular attention was paid to the collection and disposal of night soll and to the bacteriological sampling of the night soil conser- vancy tankers. All inoculation centres were re-opened for cholera im- munization and just over one million people were inoculated during the period of the outbreak.

83. It was possible to conduct a detailed epidemiological investiga- tion of each case that occurred and the results were consistently baffling. Specimens of foodstuffs in the infected promises were all cultured and were all negative for cholera. Positive swabs were, however, obtained from certain of the latrine buckets, from a chopping block used for the preparation of food in one instance, and in several cases from water in kitchen drains and on floors. One roof tank used for flushing a water closet yielded vibrios but the well which supplied the tank was negative. $4. On the night of the 10th September, nearly three weeks after the first case occurred, the first positive culture of cholera vibrios was obtained from a tanker containing communal night soil. This was in the course of routine random sampling and thereafter all night soil tankers in use in the urban areas of Kowloon and Hong Kong Island were sampled twice nightly. An interesting picture emerged. Within the next 10 days positive cultures of cholera vibrios were obtained from tankers serving 12 collection routes in Kowloon and 10 districts on the Island. It was possible in three instances to trace the infection back through the hoppers serving the tankers to latrine buckets. One bucket came from a public latrine and further investigation was not possible. However, in the two other instances, one in a tenement building and the other in a roof top squatter community, it was possible to obtain rectal swabs from the residents using the infected pail. All these swabs

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proved to be negative. Positive cultures continued to be obtained from the communal night soil over a period of twenty-six days.

85. On Monday the 8th of October, no case having occurred since the 20th of September, the Colony was declared free of infection. The following Saturday, the 13th of October, another case of cholera was confirmed; this occurred in a fishing village in the district of Yuen Long in the New Territories. In view of the fact that vibrios had disappeared from the communal night soil in the urban areas and that this particular village community could be readily controlled from a quarantine point of view, only the District of Yuen Long was declared an infected local

arca.

86. Epidemiological investigations again revealed a very interesting situation. The community consisting of 410 people were all rectally swab- bed and a total of 16 contact carriers were confirmed and placed in quarantine. Two of the contact carriers were members of the patient's Family and of the others ten were children below the age of 10 years. all of whom had close physical contact in the home or at play.

87. Intensive sampling of the water of the tidal river by which the village was situated and of the surrounding ponds used for the rearing of fresh water fish produced no cholera vibrios either agglutinable or non-agglutinable. All foodstuffs, particularly fish and fish fry, and other possible sources of infection were also consistently negative. The only common source of infection appeared to be the child contact carriers who played together on the mud banks and swam in the river.

88. The contact carriers were all treated with oral streptomycin and isolated until three successive negative specimens of stool had been obtained. No further clinical cases appeared and the district was declar- ed free of infection on the 29th October.

89. It is believed that Hong Kong was free of cholera vibrios during the period November 1961 to August 1962. Throughout this time, on a routine basis, all specimens sent to the Government Institute of Patho- logy from cases of gastro-enteritis were investigated for cholera vibrios. The first positive culture obtained was from the first case of cholera which appeared on the 22nd of August. The sampling of communal night soil tankers, which had been carried out three times each week throughout this period, gave entirely negative results until after the first case of cholera had been confirmed. It was only some 18 days later that cholera vibrios began to appear in the night soil and over the next two works there was a very widespread dissemination of the infection

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