Juvenile tuberculosis in New Zealand: with special reference to the milk supply, the incidence of bovine tuberculosis, and the type of bacillus in the tubercular lesions of children: with 33 tables and 10 graphs
1. The area of the Dominion of New Zealand is 103,581 sc;uare miles and the population at the 1916 census wa:- 1,175,000. The density of the population (10.64 persoi_s to the square mile) is such that there is little question of overcrowding and its attendant drawbacks as far as the health of the population is concerned.
2. The climate, as reflected by the amount of sunshine, moderate rainfall, prevailing winds and. temperature, is one which on the whole is favourable for those subject to respiratory catarrhs, or other respiratory diseases including tuberculosis.
3. The social conditions of the people are in advance of those obtaining in many older countries, and are part- ly reflected in the low death rate which averaged 9.33 per 1,000 of the population in 1909 -13, and in the low infantile mortality rate whic h is under 50 per 1,000 births.
4. Tables and Graphs show that the mortality from all forms of Tuberculosis and from Pulmonary Tuberculosis is very much lower in New Zealand and Australia than in most other countries. There has not been the same steady decline in this mortality in New Zealand as there has been during the same period in England and Wales, although at all . times the New Zealand rate has been lower. Thus the death rate from Tubercular Di- seases fell from 9.31 per 10,000 of the population in 1907 to 6.74 in 1916. in England and. Wales the rate in '1907 was 16.67 and in 1913 it had fallen to 13.39.
The effort to control Tuberculosis in Gt. Britain has been greater and more sustained than been the case in New Zealand.
5. The improvement in the tubercle mortality may also be expressed in percentages. Thus during the period 1871 -1913 the New Zealand rate had fallen 47%? while the rate for England and dales has fallen approximately 60%.
6. The mortality rates for Pulmonary Tuberculosis are also much lower in New Zealand than in Great Britain. The rate in New Zealand has fallen from 7.76 per 10,000 of the population in 1901 to 5.38 in 1916. That for England and "Vales for 1901 was 12.64 and for 1913, 9.80. ln Scotland during 1901 -5 the rate was 14.45 and during 1906 -7 it was 13.58.
7. A study of the age and sex distribution of tubercle mortality shows that the female death rate exceeds the male rate to a slight extent.only,between the ages of 6 and 18, but after that the male rate exceeds the female rate especially in the 20 -25 year age period. The female rate falls more quickly than the male rate after the age of 35 years.
The incidence is thus marked in males during the 20 -25 year period and after 35 years of age.
8. A study of the age and sex distribution of phthisis mortality shows that the rate in males rises from 0.43 per 10,000 in the 10 -15 year age period. to 5 .66 in the 15 -25 year period, reaching a maximum in the 25 -35 year period of 9.8 per 10,000.
The female rate is higher than the male during the 10 -15 year period (0.82 as against 0.43 in males) and also exceeds the male rate in the 15 -25 year age period (7.2 as against 5.6). Thereafter the male phthisis rate exceeds the female in each age group, the female rate falling much more rapidly than the male rate after the 35 -45 year age period.
9. Evidence has been collected from various sources -(viz. by circularising medical practitioners, from hospital outpatient returns, from post-mortem records, from the returns of School Medical Officers ,and as the result of Tuberculin tests) which go to show that tuberculosis in Children in New Zealand is very much less than in most other countries, and this good for- tune is shared by Australia. The striking difference between New Zealand and England x 'dales/ and in New Zealand's favour, is shown in the Tables and Graphs .
10. An investigation of the milk supply of Dunedin in which 200 samples of mixed milk were submitted to the usual tests for the detection of living tubercle bacilli, showed that only two, or one per cent, were positive. An examination of over 600 samples from the various parts of.New Zealand was undertaken by /Government Agricultural Dept. and all were found negative. On the hand, is estimated about 10 per cent of milk samples in Britain are tubercular. This great difference in New Zealand's- favour is pointed out and the conclusion come to that it is partly responsible for the low incidence of Tuberculosis in New Zealand children.
1. Tuberculosis is not uncommon in cattle in New Zealand and when the figures given in the .text are considered with the results of milk examinations for tubercle bacilli, one would expect a greater percent- age of tuberculous milk. The reasons advanced are that the. system of inspection in New Zealand is under, central control, and is much more thorough than in Gt. Britain.
The system of compensation and compulsory notification, along with this inspection,tends to eliminate the tuberculous dairy cow before it becomes a source of danger and when once detected prevents its milk from again being used for human consumption.
12. The type of tubercle bacillus in the tubercular lésions of New Zealand children has been investigated. The technique followed has been fully explained. Suspected material was after suitable treatment injected into guinea pigs and from the lesions which developed cultures were prepared, and from the growths obtained rabbits were inoculated to determine the type of tubercle bacillus in each case.
Th rty specimens only were obtained over a period of several years. prom these cuitures were obtained and d.L 30 rabbits inoculated in 24 oases. in si±^ cases the guinea pig tests were negative, the material being either non - tubercular or the tubercle bacilli dead.
Twenty of the 24 cases were infected by the human rt.=. type of tubercle bacillus and four by,bovine type of tubercle bacillus, the percentages being 8303% human, and 16.66¡ bovine. The percentage of bovine infections is lower than that recorded by many other workers.
The difficulty of obtaining tubercular material for this part of the investigation. further emphasises the low incidence of Tuberculosis in New Zealand children. That 16.66 per cent of the lesions investigated were due to the bovine tubercle bacillus is not surprising considering the prevalence of tuberculosis in cattle in New Zealand.