INTO AN OF AN ENQUIRY OUTBREAK 1 CHOLERA IN BURMA WITH SPECIAT REFERENCE TO THE VALUE OF PREVENTIVE INOCULATION By C. A. BOZMAN CAPTAIN, I.M.S. Assistant Director of Public Health, Burma and E. G. LEWIS Lecturer in Mathematics, University of Rangoon This account deals with the cholera epi- demic which occurred in four districts of Lower Burma during the period November 1934 to May 1935. The measures taken to combat the epidemic consisted of : (1) Disinfection of drinking supplies. (2) Disinfection of infected houses. (3) Treatment of cases (mostly in private houses). (4) Isolation (as far as practicable when dealing with the rural community). (5) Mass preventive inoculation with Kasauli anti-cholera vaccine, dose 1 c.cm. With regard to this last measure, only those actually suffering from fever and very young infants were excused. Otherwise, the epidemic staff made every endeavour to inoculate as many as possible of the men, women and children exposed to risk in the areas visited. Records were kept at the time of all who were inoculated, and, from these and the reports that reached the office of the Director of Public Health, the following tables have been com- piled. The tables show the incidence of cholera for the period November 1934 to May 1935 in the rural areas of Myaungmya, Bassein, Pyapon and Maubin districts. The population at risk has been arrived at after a very careful consideration of all the reports received throughout the epidemic. It is the total population of the particular village tracts visited during the epidemic by the public health staff, and is not the population of the whole township areas in which these village tracts are situated. Village tracts were visited either because actual cases were reported as having occurred, or because it appeared likely to the epidemic staff that the particular tract was in danger of infection. In Myaungmya and Pyapon districts there were whole-time district health officers and in Bassein there was an assistant district health officer. It is considered that the cases reported to have occurred among the population in- oculated and at risk represent the true state of affairs. It is unlikely that such cases would not have been reported to the epidemic staff even in the absence of the direct enquiries that were, in fact, made. These enquiries, it may be mentioned, were not entrusted to subordinates. 648 THE INDIAN MEDICAL GAZETTE [Nov., 1936 Myaungmya district (rural areas excluding towns) Total population at risk = 220,413 Inoculated persons Uninoculated persons Total Total Number of attacks each deaths each inoculations month month each month Attacks Deaths Attacks Deaths November 103 92 11,923 101 92 December 131 124 12,940 130 123 January 146 134 9,807 144 133 February 54 45 8,468 53 44 March 30 22 3,383 30 22 April 63 58 3,909 63 58 May 23 22 4,387 22 21 Total 550 497 54,817 543 493 Bassein district (rural areas excluding towns) Total population at risk = 62,004 Inoculated persons Uninoculated persons Total Total Number of attacks each deaths each inoculations month month each month Attacks Deaths Attacks Deaths November 27 25 746 27 25 December 34 30 3,681 34 30 January 119 104 10,591 119 104 February 52 50 12,600 51 '49 March 12 11 2,542 12 11 April 8 77 8 May 6 nil 6 Total 258 234 30,237 257 233 Pyapon district (rural areas excluding towns) Total population at risk = 121,266 Inoculated persons Uninoculated persons Total 1 Total Number ot attacks each deaths each inoculations month i month each month Attacks Deaths Attacks Deaths November 78 72 5,727 77 71 December 172 160 13,466 172 160 January 95 83 7,893 95 83 February 43 38 4,436 43 38 March 186 162 21,083 183 159 April 188 132 14,174 186 131 May 28 19 2,534 28 19 Total .. 790 666 69,313 784 661 Nov., 1936] CHOLERA IN BURMA : BOZMAN & LEWIS 549 Maubin district (rural areas excluding towns) Total population at risk = 143,218 Inoculated persons Uninoculated persons of Total Total i Number , inoculations attacks each deaths each month Deaths Attacks Deaths month month each Attacks I 2 2 2 2 November .. .. 15 14 15 14 December .. .. 65 65 3,872 94 January .. .. 94 126 116 126 116 S,582 .. .. 65 February j 65 7,470 65 March .. .. 65 99 90 90 12,461 .. .. 99 33 April | 33 5.281 37 .. 37 May .. 438 385 385 37,669 Total .. ; 438 It is difficult to avoid the conclusion that The epidemic staff worked hard and allowed inoculation. cases inoculation did not a in these produce immunity. only short interval to from receiving A3 and A4.?A interval between inocula- a elapse Cases long report of a case in the rural areas and arriv- tion and attack and the fatal issue suggests that if on it had ing the spot to carry out general sanitary immunity had existed disappeared. Case A5.?This but this measures and inoculation. These measures patient recovered, possibly should not be attributed to inoculation 4 were in only days directed, the first instance, against the before onset. case contacts and the infected houses. Their Case B1.?Similar to case A1 and the same remarks efficacy may be judged qualitatively from the apply. fact that the figures for the recrudescence of Case B2.?This was a very old lady, stated to be the over 80 years. disease in and tracts were villages village Cases B3, Bi and B7 followed the expected course; small. invariably that is to say, they were inoculated in time for The following table gives details of the protection to develop and when attacked they recovered. B5 B6 were contacts a case attacks reported among the inoculated m the Cases and of fatal and it would that there was no time for districts in question. The number of such appear protection to develop before the disease appeared. detailed cases was not to large enough attempt Case CI is similar to cases A1 and Bl, and the same drawing conclusions statistically :? remarks apply. inoculated and at risk in (A) district Details of attacks among the population Pyapon (rural area), and (C) Bassem district area), {B) Myaungmya district {rural (rural area) Interval Attacked Inoculated between inoculation Sex on on and Result Township attack M. 1-12-34 30-11-34 24 Al. hours | Died. Kyaiklat F. 23-3-35 24-2-35 27 A2. days Bogale F. 28-3-35 10-1-35 77 A3. F. 30-3-35 10-1-35 79 ? A4. F. 2-4-35 29-3-35 4 ? A5. Recovered. 29-3-35 M. 18-4-35 20 ? Died. A6. ? M. 30-12-34 29-12-34 24 hours Bl. Moulmeingyun F. 25-2-35 22-12-34 65 B2. days M. 19-11-34 14-11-34 5 ? Recovered B3. Myaungmya M. 26-11-34 20-11-34 6 ? ? B4. i . F. 21-1-35 20-1-35 24 hours Died. B5. M. 22-5-35 I 22-5-35 12 ? B6. F. 5-1-35 26-11-34 40 Recovered. B7. Einmc ! days F. 5-2-35 | 6-2-35 24 hours Died. CI. Ngathainggyaung Comments on above cases Subject to limitations mentioned later Case that this man was Al.?It would appear the of the the incubating the disease when inoculated and cholera regarding homogeneity material, tables are as a developed before protection. following presented statistical Cases A2 and A6.?'These were attacked within a test of the association of inoculation with month of inoculation and later than one week after exemption from attack. Several such tables 650 THE INDIAN MEDICAL GAZETTE [Nov., 1936 were compiled and analysed for separate towns cases where the tests could be validly applied, and districts in different months, and in all similar results to those above were obtained*. The figures in brackets denote the frequen- Rural area, Myaungmya cies to be expected on the hypothesis that in- oculation and exemption from attack are in- January 1935 dependent. The other figures represent the observed The of the Not frequencies. application Attacked Total ex- attacked X2 test shows that in no table where the pected frequencies are sufficiently large can inoculation be said not to be asso- Inoculated at 2 24,860 24,862 positively risk. (16.48) (24,845.52) ciated with exemption from attack; in other words, the observed differences between the 144 Not inoculated 195,191 195,335 actual frequencies and those expected on the at risk. (129.52) (195,205.48) hypothesis of independence are too large to be Total 146 220,051 220,197 considered as having arisen by chance. The sense of the association is obvious from the P = 0.00015. tables and there seems to be a strong case in favour of inoculation with this particular vaccine as a but the Rural Bassein prophylactic measure, area, methods available for testing the degree of the February 1935 association in fourfold tables such as the above involve assumptions which, we think, prejudice Not their usefulness. Attacked Total attacked The measure of the discrepancy between observation and hypothesis is, if anything, an Inoculated at 1 15,017 15,018 under-estimation of the actual position. The risk. (12.63) (15,005.37) number of uninoculated at risk is probably in- Not inoculated 51 46,776 46,827 over-estimated whereas the number of at risk. i (39.37) (46,787.63) oculated at risk in any particular month is somewhat under-estimated.