not one of the eight cases occurring in inoculated persons aged 45 years and over was of a severe nature. It is possible, however, that other factors may be involved and this is worthy of further study.
85. In addition to the 106 carriers found amongst contacts of cases, a further 14 were traced through nightsoil sampling. Out of the total of 120 carriers, 68, or 56.7 per cent, had been inoculated. It is of interest that this level of inoculation is below that of the population and also that age pattern corresponds closely to the age structure of the popula- tion whereas the sex distribution is similar to that of the cases. The results are detailed in Table 10.
TABLE JO
CHOLERA CARRIERS BY ACE AND SEX
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30444
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M F
12
5-9
F
45-59
60-4-
Total
M F
** F
As
F
M
f
10 3
15
32 15
5
2
3
77 43
% of carriers...
16.7
10.8
17.5
39.1
117
4.2
100
%% of age-group
in population
15,3
13.7
34.8
34.8
12.3
5.1
100
86. Twenty-five per cent of the urban population, i.c. 33% of Hong Kong and 19% of Kowloon is not yet served by a water sewerage system and, commencing September, 1962, all nightsoil collecting vehicles were tested nightly for the presence of the vibrios of cholera El Tor. Nightsoil pails are collected from houses cach night on demarcated routes; cach pail is emptied into a hopper which in turn is pumped into a tanker. Two samples were taken from each tanker at the final disposal points and sent immediately for culture. During the year, at one time or another, 31 out of 34 routes in Hong Kong and all 28 routes in Kowloon were found to be infected. The first positive sample was obtained on 1st July, four days after the first case presented. Thereafter, Hong Kong routes were positive on over 700 occasions and Kowloon routes on almost 400 occasions. Distribution appeared to have no direct relationship to cases and followed rather than preceded them. Positive results were sporadic during the months of July, August and September, but there- after the infection was heavy and sustained until late October in Kowloon and late November in Hong Kong. Subsequently, positive results rapidly became intermittent once more and finally ceased.
87. From the beginning of the outbreak until the end of September, a team of Health Inspectors attempted the tracing of excretors of the
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vibrio through the nightsoil sampling. All hoppers supplying a tanker notified as positive were sampled and almost one hundred such samples yielded vibrios. Following the report of a positive hopper, all nightsoil buckets emptied into the hopper were then swabbed and on more than twenty occasions positive pails were found; all members of the house- holds using these pails were swabbed rectally. By these means, fourteen symptomless excretors of vibrios were discovered and were isolated together with their immediate contacts, 227 in number.
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These investigations did not produce any associations with clinical cases and, when pressure on the laboratories became excessive in September, the tracing of excretors of vibrios by this means had to be abandoned. However, routine sampling of nightsoil tankers was continued, and has proved a reliable means of estimating the incidence of infection in the community.
89.
Several investigations were undertaken into the distribution of vibrios amongst the lower income groups. More than 3,400 individuals from amongst remand prisoners, illegal and other immigrants and night- soil workers were rectally swabbed. Only one positive result was discovered in a nightsoil worker; this was from a total of 950 such workers who are exposed to great risk of infection.
90.
Summarizing the outbreak, it may be said that there was evidence of widespread dissemination of the vibrio throughout the population. ile, symptomless carriers, particularly in the latter part of 1963. In spite of this, comparitively few cases were reported although very intensive case-finding measures were continuously in force.
Notifiable Diseases
91. During 1963 there was a decrease of 1.2% in the overall incidence of notifiable disease. This was mainly due to a marked fall in the notifica- Lions of poliomyelitis, tuberculosis, diphtheria, malaria and influenza. This fall was counteracted by increases in notifications of measles, chicken- pox, cholera, enteric fever and dysentery, both bacillary and amoebic.
92. Free immunization against smallpox, enteric fever, diphtheria and cholera continued to be available to all members of the public at all Government hospitals. clinics, Port Health inoculation centres. District Health Offices and Maternal and Child Health Centres. Registered doctors in private practice were issued with supplies of smallpox and cholera vaccine, free of charge. In addition, inoculation teams visited
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