M 167
In a detailed survey (q.v.) of the problem in general and the rat-fleas of the Colony in particular, I have shown that the common rat-flea, here, is Xenopsylla cheopis and that the general Cheopis Index is as high as 4.82. As many as 50 of these potential plague-carrying fleas were found on one rat.
Taking the figures of Seasonal Plague incidence for the last ten years, it is shown that the greatest number of cases occurs in May, with next highest figures in June and April, and that these months are directly correlated with the highest Cheopis counts and the maximum Relative Humidity.
The regional incidence also corresponds with the highest Cheopis Indices and the largest numbers of plague-infected rats. The districts most heavily involved are those already noted for the high incidence of other diseases: namely Nos. 1A & 2A (1 & 2) and Nos. 9 & 10. There is more than a casual relation between this disease and the centres of overcrowding and small-shipping activity. These districts are certainly the primary centres of danger.
The four cases of 1928 all occurred in Nos. 1 & 2 Districts, in the months of May, June, and July.
The following table shows the monthly incidence of plague for the last ten years and decennial totals of human and rat cases.
Month 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 Monthly Totals (Human) Monthly Totals (Rat plague) January 2 3 2 11 3 1 23 2 33 February March 30 74 2 107 1 April 94 9 5 247 10 365 34 May 171 28 28 454 47 730 68 June 132 56 64 237 49 539 40 July 20 24 77 23 171 5 August 4 14 29 10 63 September October November 8 14 I 1 433 7 December 12 10 ON 20 2 10 Total 464 138 150 181 1.48"Preliminary Rat-flea Survey and some other notes on its Relation to Local Plague, Hong Kong, 1928." (H. A. Fawcett).