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M
(j) The relation of carriers to the epidemic. No extensive work could be done upon contact carriers at the time of the epidemic, as I arrived in Hongkong at the time of its subsidence. However, in the following, I shall discuss the results obtained by Drs. Macfarlane and Earle, who made several cultures upon contacts of cases in Hongkong and my own investigations upon the inmates of the Victoria Gaol.
(1) Contact carriers.--Drs. Macfarlane and Earle's investigations extended from March 11th to May 13th and include cultures made as routine examinations of contacts with patients for the presence of the meningococcus in the nasopharynx. It appears that the work was very carefully done; only a few cultures were examined at a time and all plate cultures contaminated with saliva were discarded. The criteria for recognition of the meningococcus were (1) typical colony morphology; (2) absence of pigment; (3) acid production in dextrose and maltose and not in saccharose medium; (4) typical mor- phology by Gram's stain; (5) ready emulsification of the growth on subcultures. No agglutination tests were made, however. Sheep-serum water (1 part to 2 parts water) 20 per cent. agar, was used for the plate cultures.
Examining contacts of several patients, they found that :-
71 Europeans yielded seven carriers (98 per cent.)
133 Chinese yielded nine carriers (6'7 per cent.), making a total of 204 yielding
sixteen carriers or 7'8 per cent.
This is on the basis of a single examination.
The ratio of incidence of meningitis amongst the Europeans to the white population is as 1:1250; in the case of the Chinese to the coloured population as 1:509.* These cultures were taken at the height of the epidemic but the number of contact carriers in the both series are lower than is usually the case. One deduction however, can be made, namely, that the carriers are more prevalent among the Europeans, notwithstanding the fact that fewer were afflicted.
(2) Non-contact carriers.-As no opportunity presented itself to continue the study of contact carriers, my attention was paid to a class which may only be regarded nominally as non-contact carriers. In the event of an epidemic of such great extent as this one, a class can hardly be chosen as a representative non-contact group. It was finally decided that the Victoria Gaol, in which no cases have developed throughout the epidemic and having a daily average of six hundred inmates, would offer a suitable source for determination of the number of healthy carriers. The prisoners are, in the main, previous residents of Hongkong and the length of confinement varies from a few days to several years.
In interpreting the results these factors must be considered. The prisoners are kept isolated in individual cells; there is no overcrowding; sickness is promptly attended to. In other words, the sanitary conditions in the prison are better than in a great part of the Chinese community.
The following cultures were made on uulaked sheep-blood, veal-infusion agar with one per cent. dextrose (defibrinated blood, 1 part; agar 15 parts). The cultures were taken from the nasopharynx by means of a West swab, care being taken to avoid con- tamination with saliva. The plates were immediately incubated after inoculation. Each person's culture was made on one entire plate.
The results are as follows:-
The total number of Chinese prisoners swabbed
151
Plate cultures contaminated with saliva and therefore discarded (saliva has an inhibitive effect upon the growth of the meningococcus)
21
** The Hongkong Blue Book for 1917: white population 5,000; Chinese 530,100. The census was taken in 1911, but is estimated for 1917.
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