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The significance of the “zymotic death rate”
THE f
S I G N I F I C A N C E OF T H E
"ZY.~'IOTIC D E A T H R A T E . "
11
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1893 I attributed the marked decrease in the deaths from these diseases which I then reported to the exceptionally warm and dry summer which we had experienced. I am happy, however, to be able to point out that the improvement still continues, notwithstanding that during the past y e ~ the weather was, during the summer at least, in marked contrast to that of the year preceding it, with much moisture and a comparatively low temperature. The chart (given in the original report) shows that the deaths from phthisis seem to be but tittle influenced by the state of the weather or the season of the year. The deaths from this cause were most numerous (33) in the first week in April, and lowest (8) in the fourth week in September ; in the last week in December the number was only x i ; whilst, on the other hand, the severe, inclement, and very cold weather told heavily in increasing our mortality from diseases of the respiratory organs. There seems to be but little relation between the mortality arising from these diseases. I regret that I cannot give even an approximate idea of the number of cases of diseases of the respiratory organs occurring amongst us, nor can I specify the form of lung affection which they assume, or which of them causes the greater number of deaths. I think, however, that bronchitis, both acute and chronic, is accountable for the majority thereof. The ngture of the employment of a large number of our people, the sudden transition from the heated mill or factory into the damp, cold outer air, with often insufficient clothing and but little heat-producing food, rendering them most susceptible to this disease ; and when to these is added the irritation of the air passages produced by the particles of textile matter suspended in the air of the factory, it is not to be wondered at that bronchitis is so prevalent with us, as it undoubtedly is ; and I believe that it is the cause of the great majority of the deaths attributable to diseases of the respiratory organs. Phthisis is essentially a disease of overcrowding and bad ventilation. The public generally do not seem to realise this fact, nor do they consider the somewhat infectious nature of the disease. It is the scourge of the working classes, and is mainly due to unsanitary surroundings and ill-ventilated dwellings. The ventilation of the working man's dwelling is the least and last consideration of the builder, and light and air strive too often in vain for an entrance therein. The effect of good sanitary work in reducing the death rate from this disease has been very marked, not only on the Continent, but in the sister countries. Unfortunately, in this country but little sanitation has been thought of, and matters remain, at present, in much the same unsatisfactory condition in which years ago we found them. Want of exercise, improper food, and impure air, more especially that rendered so by respiration, or exhalations from the body, have a most material effect in the causation of this
disease, and increasing its mortality. Naturally, those working in close rooms are affected most, whilst those who pursue their avocations in good, fresh, open air are least liable to suffer from it. In the army an increase of cubic space to each man, and the removal of foul air, caused a notable decline in the number of deaths from this cause. No other remedy was employed. In many of the sanatoriums, where invalids suffering Jrom this disease resort with much benefit, the cold, though very great, does not injuriously affect them, accompanied, as it generally is, with dry air and much sunlight. We, unfortunately, have the disadvantage so common to Ireland, of a copious rainfall, a constant moisture in the air, and the sun only too rarely shines brightly upon us. Our heavy clay soil is very retentive of damp, and there can be but little doubt that the drying of the soil and air which more or less always accompanies efficient drainage, would tend considerably to the diminution of this disease, so prevalent in our midst. THE SIGNIFICANCE OF THE " ZYMOTIC DEATH RATE." v BY T.
ORME
DUDFIELD,
M.D., M.O.H. of Kensington.
ZYMoTIc diseases have a special interest for sanitarians, being of a more or less preventable character ; the absence or the prevalence of certain of them therefore, is regarded as a test of the sanitary condition of a district. But, without underrating the importance of this test, it must be said that there are limitations to its applicability necessary to be borne in mind in drawing inferences from mere numbers. What I mean may be best explained by illustrations, founded on our own local experience within the last few years. Thus, measles was very prevalent in 1888, 189o , 1892 , and in 1894 , the deaths being considerably above the average. In 1889, 1891 and 1893 on the other hand, the deaths from this cause were greatly below the average ; but the lowered mortality, regarded as evidence of the diminished prevalence of the disease, was the natural consequence of its excessive prevalence and fatality in the preceding years. In saying this, I must not be thought to ignore the fact that the type of one epidemic of a zymotic disease may be more severe than that of another ; or that the relative severity of an epidemic may be influenced by the measures taken, or the neglect to take measures, to check the spread of infection. Again, the number of deaths from whooping-cough in 1889 was the lowest on record; it is not surprising to find, therefore, that in the immediately preceding and succeeding years this disease was fatal above the average ; the large total of 185 deaths in 1878 , moreover, followed the then minimum return of thirty-four in the previous year. * From Dr. Dudfield's A.nnual Report for I894.
12
TENEMENT
D W E L L I N G S IN NEW Y O R K .
Diarrheea may be cited as an illustration of quite another kind. The mortality from this disease amongst infants was excessive in 1887 ; the mortality in ,888 was much below the average; but the diminished mortality in i888 had no relation to the excessive mortality in i887. The conditions were altogether different ; the summer of 1888 was cold and wet, and, as always happens in these circumstances, the mortality from infantile diarrhoea was low--just as it is always high when the summer is hot and dry, as in 1887. Again, the significance of a high rate of prevalence of enteric fever varies widely in different circumstances. This disease may be constantly present in one district, as a result of drainage defects or of a polluted water supply ; whilst in another district its introduction may be wholly accidental, as when it is due to casual pollution of water, or to a specifically contaminated milk supply introduced from without. These and like circumstances must be kept in view, if we would draw sound conclusions from a high or a low rate or prevalence of zymotie diseases, particularly in relation to the sanitary condition of a district. Subject to corrections for local circumstances, for climatic influences, and for high rates in previous years, the concurrence of a low zymotic death rate with a low general death rate, furnishes just ground for satisfaction. For some years past the general rate and the zymotie rate had both been below the decennial average in Kensington. In 1894 the general rate was (as in London also) below the average; the zymotic rate was average. It need hardly be said that a 2)ersistentZy high rate of mortality from zymotic diseases furnishes matter for serious consideration. Kensington has hitherto been fortunate in having a death rate from these diseases much below that of the metropolis generally. TENEMENT DWELLINGS IN NEW YORK. AN attack has been recently made on the sanitary condition of the Tenements of Trinity Church, in New York. An able defence of these Tenements has been published by Mr. F. L. Hoffman, who evidently speaks with actuarial knoMedge and skill. The charge made against the sanitary condition of the Trinity Tenements consists in the main in the statement that the death rate in them was 35 per cent. in excess of the general death rate of the City of New York. This method of comparison is rightly objected to. " T h e fallacy involved in the comparison of two populations so essentially different in numbers, is plain. The law of large numbers eliminates the possibility of accidental occurrences and accidental influences in the death rate of the population at large, which is not the case in the calculation of a death rate based on small populations. If, for instance, the 326 suicides that occurred in the City of New York
during 1894 were omitted in the calculation of the general death rate, this would only affect the rate per i,ooo by o"I7, but if the one suicide that occurred in t894 among the population of Trinity Tenements were omitted, this would affect the Trinity death rate by 0'43 per i,ooo. Or, in other words, 843 deaths could be omitted from the total mortality of the city before such an omission or element of error would affect the general death rate to the same extent as the accidental omission or addition of one death would affect the Trinity Tenement death rate." Mr. Hoffman then proceeds to quote various English and other authorities in support of his contention that the above method constitutes a violation of the fundamental principles of vital statistics. H e further shows that a considerable proportion of the excess in the death rate of the Trinity Tenements over that for New York as a whole is caused by the latter being based on an erroneously estimated population, while the former is based on a rigidly enumerated population. Having shown the fallacies of the methods employed, Mr. Hoffman proceeds to show that four methods of comparison might have been legitimately employed. (a) The Trinity death rate might have been compared with that of District A, Ward 8, within which the tenements are situate. Such a comparison shows in 1891 a death rate of 28"5 for the whole ward, and of 2 i'7 for the Trinity Tenements. (#) Other tenement dwellings might have been compared with the Trinity Tenements. Such a comparison when made is very /'avourable to the latter.. (c) A modification of (a), using the comparative statistics of six years, shows a mean death rate of 31"39 in District A, Ward 8, as compared with 28-73 in Trinity Tenements. (d) The fourth method being dependent on a knowledge of special local considerations need not be further considered. Having shown by these methods, that the general death rate of the Trinity Tenements is not so high as that of fairly comparable populations, Mr. Hoffman makes a detailed comparison for certain diseases. Comparing Ward 8 with the Trinity Tenements, it is plain that the death rates from scarlet fever, diphtheria and croup, typhoid fever and diarrhoeal diseases, are very much lower in the latter than in the former, while that from measles is considerably higher. These results coincide very closely with the results of a similar investigation of Peabody Buildings in this country. So also does the fact that the death rate among children under five years of age is considerably lower than that in Ward 8, District A, and somewhat lower than that in the whole city. Mr. Hoffman has not gone fully into the influence of age-distribution of the special population of the Trinity Tenements ; but he promises this in a later and fuller report. This wiU be of great value, and will be looked for by all who are
S I G N I F I C A N C E OF T H E
"ZY.~'IOTIC D E A T H R A T E . "
11
. . . . . . . . . . . . .
1893 I attributed the marked decrease in the deaths from these diseases which I then reported to the exceptionally warm and dry summer which we had experienced. I am happy, however, to be able to point out that the improvement still continues, notwithstanding that during the past y e ~ the weather was, during the summer at least, in marked contrast to that of the year preceding it, with much moisture and a comparatively low temperature. The chart (given in the original report) shows that the deaths from phthisis seem to be but tittle influenced by the state of the weather or the season of the year. The deaths from this cause were most numerous (33) in the first week in April, and lowest (8) in the fourth week in September ; in the last week in December the number was only x i ; whilst, on the other hand, the severe, inclement, and very cold weather told heavily in increasing our mortality from diseases of the respiratory organs. There seems to be but little relation between the mortality arising from these diseases. I regret that I cannot give even an approximate idea of the number of cases of diseases of the respiratory organs occurring amongst us, nor can I specify the form of lung affection which they assume, or which of them causes the greater number of deaths. I think, however, that bronchitis, both acute and chronic, is accountable for the majority thereof. The ngture of the employment of a large number of our people, the sudden transition from the heated mill or factory into the damp, cold outer air, with often insufficient clothing and but little heat-producing food, rendering them most susceptible to this disease ; and when to these is added the irritation of the air passages produced by the particles of textile matter suspended in the air of the factory, it is not to be wondered at that bronchitis is so prevalent with us, as it undoubtedly is ; and I believe that it is the cause of the great majority of the deaths attributable to diseases of the respiratory organs. Phthisis is essentially a disease of overcrowding and bad ventilation. The public generally do not seem to realise this fact, nor do they consider the somewhat infectious nature of the disease. It is the scourge of the working classes, and is mainly due to unsanitary surroundings and ill-ventilated dwellings. The ventilation of the working man's dwelling is the least and last consideration of the builder, and light and air strive too often in vain for an entrance therein. The effect of good sanitary work in reducing the death rate from this disease has been very marked, not only on the Continent, but in the sister countries. Unfortunately, in this country but little sanitation has been thought of, and matters remain, at present, in much the same unsatisfactory condition in which years ago we found them. Want of exercise, improper food, and impure air, more especially that rendered so by respiration, or exhalations from the body, have a most material effect in the causation of this
disease, and increasing its mortality. Naturally, those working in close rooms are affected most, whilst those who pursue their avocations in good, fresh, open air are least liable to suffer from it. In the army an increase of cubic space to each man, and the removal of foul air, caused a notable decline in the number of deaths from this cause. No other remedy was employed. In many of the sanatoriums, where invalids suffering Jrom this disease resort with much benefit, the cold, though very great, does not injuriously affect them, accompanied, as it generally is, with dry air and much sunlight. We, unfortunately, have the disadvantage so common to Ireland, of a copious rainfall, a constant moisture in the air, and the sun only too rarely shines brightly upon us. Our heavy clay soil is very retentive of damp, and there can be but little doubt that the drying of the soil and air which more or less always accompanies efficient drainage, would tend considerably to the diminution of this disease, so prevalent in our midst. THE SIGNIFICANCE OF THE " ZYMOTIC DEATH RATE." v BY T.
ORME
DUDFIELD,
M.D., M.O.H. of Kensington.
ZYMoTIc diseases have a special interest for sanitarians, being of a more or less preventable character ; the absence or the prevalence of certain of them therefore, is regarded as a test of the sanitary condition of a district. But, without underrating the importance of this test, it must be said that there are limitations to its applicability necessary to be borne in mind in drawing inferences from mere numbers. What I mean may be best explained by illustrations, founded on our own local experience within the last few years. Thus, measles was very prevalent in 1888, 189o , 1892 , and in 1894 , the deaths being considerably above the average. In 1889, 1891 and 1893 on the other hand, the deaths from this cause were greatly below the average ; but the lowered mortality, regarded as evidence of the diminished prevalence of the disease, was the natural consequence of its excessive prevalence and fatality in the preceding years. In saying this, I must not be thought to ignore the fact that the type of one epidemic of a zymotic disease may be more severe than that of another ; or that the relative severity of an epidemic may be influenced by the measures taken, or the neglect to take measures, to check the spread of infection. Again, the number of deaths from whooping-cough in 1889 was the lowest on record; it is not surprising to find, therefore, that in the immediately preceding and succeeding years this disease was fatal above the average ; the large total of 185 deaths in 1878 , moreover, followed the then minimum return of thirty-four in the previous year. * From Dr. Dudfield's A.nnual Report for I894.
12
TENEMENT
D W E L L I N G S IN NEW Y O R K .
Diarrheea may be cited as an illustration of quite another kind. The mortality from this disease amongst infants was excessive in 1887 ; the mortality in ,888 was much below the average; but the diminished mortality in i888 had no relation to the excessive mortality in i887. The conditions were altogether different ; the summer of 1888 was cold and wet, and, as always happens in these circumstances, the mortality from infantile diarrhoea was low--just as it is always high when the summer is hot and dry, as in 1887. Again, the significance of a high rate of prevalence of enteric fever varies widely in different circumstances. This disease may be constantly present in one district, as a result of drainage defects or of a polluted water supply ; whilst in another district its introduction may be wholly accidental, as when it is due to casual pollution of water, or to a specifically contaminated milk supply introduced from without. These and like circumstances must be kept in view, if we would draw sound conclusions from a high or a low rate or prevalence of zymotie diseases, particularly in relation to the sanitary condition of a district. Subject to corrections for local circumstances, for climatic influences, and for high rates in previous years, the concurrence of a low zymotic death rate with a low general death rate, furnishes just ground for satisfaction. For some years past the general rate and the zymotie rate had both been below the decennial average in Kensington. In 1894 the general rate was (as in London also) below the average; the zymotic rate was average. It need hardly be said that a 2)ersistentZy high rate of mortality from zymotic diseases furnishes matter for serious consideration. Kensington has hitherto been fortunate in having a death rate from these diseases much below that of the metropolis generally. TENEMENT DWELLINGS IN NEW YORK. AN attack has been recently made on the sanitary condition of the Tenements of Trinity Church, in New York. An able defence of these Tenements has been published by Mr. F. L. Hoffman, who evidently speaks with actuarial knoMedge and skill. The charge made against the sanitary condition of the Trinity Tenements consists in the main in the statement that the death rate in them was 35 per cent. in excess of the general death rate of the City of New York. This method of comparison is rightly objected to. " T h e fallacy involved in the comparison of two populations so essentially different in numbers, is plain. The law of large numbers eliminates the possibility of accidental occurrences and accidental influences in the death rate of the population at large, which is not the case in the calculation of a death rate based on small populations. If, for instance, the 326 suicides that occurred in the City of New York
during 1894 were omitted in the calculation of the general death rate, this would only affect the rate per i,ooo by o"I7, but if the one suicide that occurred in t894 among the population of Trinity Tenements were omitted, this would affect the Trinity death rate by 0'43 per i,ooo. Or, in other words, 843 deaths could be omitted from the total mortality of the city before such an omission or element of error would affect the general death rate to the same extent as the accidental omission or addition of one death would affect the Trinity Tenement death rate." Mr. Hoffman then proceeds to quote various English and other authorities in support of his contention that the above method constitutes a violation of the fundamental principles of vital statistics. H e further shows that a considerable proportion of the excess in the death rate of the Trinity Tenements over that for New York as a whole is caused by the latter being based on an erroneously estimated population, while the former is based on a rigidly enumerated population. Having shown the fallacies of the methods employed, Mr. Hoffman proceeds to show that four methods of comparison might have been legitimately employed. (a) The Trinity death rate might have been compared with that of District A, Ward 8, within which the tenements are situate. Such a comparison shows in 1891 a death rate of 28"5 for the whole ward, and of 2 i'7 for the Trinity Tenements. (#) Other tenement dwellings might have been compared with the Trinity Tenements. Such a comparison when made is very /'avourable to the latter.. (c) A modification of (a), using the comparative statistics of six years, shows a mean death rate of 31"39 in District A, Ward 8, as compared with 28-73 in Trinity Tenements. (d) The fourth method being dependent on a knowledge of special local considerations need not be further considered. Having shown by these methods, that the general death rate of the Trinity Tenements is not so high as that of fairly comparable populations, Mr. Hoffman makes a detailed comparison for certain diseases. Comparing Ward 8 with the Trinity Tenements, it is plain that the death rates from scarlet fever, diphtheria and croup, typhoid fever and diarrhoeal diseases, are very much lower in the latter than in the former, while that from measles is considerably higher. These results coincide very closely with the results of a similar investigation of Peabody Buildings in this country. So also does the fact that the death rate among children under five years of age is considerably lower than that in Ward 8, District A, and somewhat lower than that in the whole city. Mr. Hoffman has not gone fully into the influence of age-distribution of the special population of the Trinity Tenements ; but he promises this in a later and fuller report. This wiU be of great value, and will be looked for by all who are