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A note on the varying prevalence of scarlet fever in relation to meteorological conditions
1914.
PUBLIC HEALTH.
A N O T E ON T H E V A R Y I N G P R E V A L E N C E O F S C A R L E T F E V E R IN RELATION TO METEOROLOGICAL CONDITIONS. Bv A. L. DYKES, M.D. (Edin.), D.P.H. (Lond.), Assistant Medical Officer of Health, Oldham. is generally I T and waning
admitted that in the waxing prevalence of the infectious fevers there are factors at work which have not been defined, The problem here presented is of supreme importance in scarlet fever because of the great outlay of public money in its hospital isolatxon. Despite the fact that there are some seven hundred hospitals largely used for this purpose, the disease on the whole is as prevalent as ever in the community, In considering the failure of hospital isolation its function in controlling infection has to be clearly recognised. To be effective it must be the complement of efficient prevention outside. This has been proved in the case of smallpox. Where an outbreak has been energetically dealt with at the outset, all actual cases being removed at once and contacts vaccinated and kept under supervision, the spread of the disease has been arrested even in closely populated areas. So far as scarlet fever is concerned outbreaks can be similarly checked, but in urban areas it is commonly endemic while the removal of cases to hospital is continually going on. Evidently the " l e a k " in prevention is too large to patch up. A very probable explanation is that not only mild ambulant cases with little more than sore throat exist, but that carriers are also common : the infection of return eases by individuals who to all clin,.'cal tests are quite normal supports the latter suspicion. Another significant and practical point is that scarlet fever varies very greatly in infectivity, as is well shown by the diverse results of barrier nursing at different times. The infectivity of a fever, whether it be due to increased virulence of the micro-organism or to low resistance on the part of susceptibles, plainly bears on the feasibility of effective prevention. As regards changes in virulence little is known, but the theory that when a new strain of scarlet fever is introduced into a district the infectlon spreads more readily and tends to be more specially severe is not without supporting evidence. If it is true, then stringent measures are required to locate the original sources of infection in a given area.
293
Facts seeming to reveal the alternative condition, namely, a more or less general fall in resistance with consequent predisposition, may be m!sleading. Apparent predisposition may be in part or wholly a question of more effective and wider exposure. Thus, it may be true that there is an age-predisposition to typhoid fever among adolescents and young adults, but at the same time this period of life, especially with the working classes, is the one of greatest freedom. The age of close parental control is past, and such possible vehicles of the infection as shell-fish, watercress, ice-cream, milk, and water are likely to be obtained under doubtful conditions. Later, when many of these people have settled down in houses of their own, their chances of exposure to infection as an age group must be far less. As a parallel instance, in the South African W a r the young soldiers suffered especially from typhoid fever, but were less careful than their elders as to the source of drinking water and the need for steritising it. Much more will have to be done before it can be said, even in a general way, how far the prevalence of scarlet fever depends on acquired predisposition and extra exposure respectively. On the side of predisposition it may be said that no evidence has been elicited. It may be, however, that catarrhal rhinitis and sore throat opens the way to scarlatinal infection. An analogous process is observed in diphtheria, for patients suffering from scarlet fever are peculiarly liable to the faucial form of that disease, while as a complication or sequel of measles it usually assumes the laryngeal form. On the other hand, scarlet fever, unlike typhoid fever, ordinarily results from close association between donor and recipient, and the problem of extensive exposure in the community thus involves the mixing of susceptibles, particularly children. With these considerations in mind, I have examined the prevalence of scarlet fever in Oldham over a period of eleven years in relation to meteorological conditions. (See table). The average humidity, average temperature, average amount of sunlight, and total rainfall for each month of the eleven years I9O2-X2 inclusive are tabulated with the number of notified cases of scarlet fever and' resulting deaths. On first examining these tables no definite correlation was observed. In noting the relation of scarlet fever to rainfall it must be remembered that, in addition to differences in temperature, the cold months are accompanied by a higher humidity and fewer hours
of sunlight than the warm months, i have on this account roughly divided each year into two periods: the cold period containing the first three and last three months, and the warm period the remainder. Months have been classed as wet or dry according as the total rainfall yielded has been greater than five or less than two inches. Those with rainfall between these amounts have been excluded from the following table :-COLD
JUNE,
PUBLIC HEALTH.
294
PERIOD.
\¥ARM PERIOD.
~st three and last three months. Intermediate sir( months, N o . of wet m o n t h s .. 21 .. 18 Average n u m b e r of cases per wet m o n t h . . ., 51 -. 44 Percentage mortality . , 3"3% -, 5'5% N o . o f dry m o n t h s ., 9 -, I3 Average number of cases p e r dry m o n t h . . . . 36 ,, 41 Percentage mortality . . 2"3°[o . . I'8°/o
It will be seen that the average number of cases for a wet month exceeds the average for a dry month in both periods. The excess is marked in the cold period and comparatively slight in the warm period. This increased average in the veer months of the cold period may possibly be dependent to some extent on greater risk of exposure to infection and heightened susceptibility. During the cold months of the year if there is much rain, susceptibles are more liable to be brought into close contact both at school and at home. At this time of the year there are fewer holidays, and in wet weather the school children usually play in covered playgrounds ; also the humidity being high and the soil damp there is a greater liability to catarrhal conditions of the throat and upper air passages, and hence increased susceptibility to the scarlet fever virus. One would expect the case mortality to be higher than in the dry months for the same reason. In wet months of the w a r m period, on the other hand, it is conceivable that these causes do not operate to the same extent. Humidity is lower and the temperature being higher there is probably not the close association which is present in the colder months. It must be remembered also that the school holidaysare longer in the warm period. It is possible also that there are causes tending in this period slightly to increase susceptibility during dry months such as ineffectual flushing of sewers and increase of dust. These assumptions are rather strengthened by the fact that a wet month following a dry one during the cold period is frequently accompanied by an increase in the number of c.ases, while during the warm period this tendency is much less marked, a decrease being quite common.
Comparing the years of the series w i t h each other, the following facts will be noted :-(1) A succession of months: each with rainfall and humidity above the average may be accompanied by an increase in the number of cases (e.g., 19o5). (z) A very excessive rainfall if sustained may be accompanied and followed by a decrease of cases (e.g., 19o3). (3) A dry warm summer is frequently followed by a definite autumnal increase (e.g., 19o2, 19o 4 , 1911). In conclusion, my thanks are due to Dr. Wilkinson, medical officer of health of Oldham, who kindly allowed me to consult his annual reports, from which all necessary statistics were obtained. PREVALENCE
OF S C A R L E T ELEVEN
FEVER IN O L D H A M ¥'EARS.
FOR
Scarlet Fever~
1902. 25N
Cases. Dealh~
z ~
L--z_'
JF e ba. n,.. .899 2 4311 ~ l ! 5 7 March.. .. .. .. .. ~gAu~ust Sept. , ,
April May June Iulv
October Nov. Dec.
.,
89 75 72 72 69 73 75 80 85 96
43 45 47 55 58 56 55 5° 45 41
8 ~
I 2ol 7
8 7½ 8½ 8 8~ ~
15 18 2I 14 28 16 23
2"29 2'48 4"64 3"5 2"49 423 5 I1 2'52 7"35 2"5r
4'48'
233 5 ~ I 45 '27 4I 4I 60 80 62 1°3 94 93
I --4 2 3 5 1 5 9 6
1903.
9° 39 89 43 80" , 44 7° 43 74 5~ . 66 56 73 60, 79 57 75 55 85 5r 91 ~ 44 86 3~
Jail.
Feb.
March April
May
June July August Sept, Oct. Nov.
Dee.
~½ 6 6~ 5"
6 8 7 7½
12 18 23 15
3,51 .t 4"58 ~ 3'54 i 1"65 !
9
2"42 6"23 7'56 " 7 54 12"°7 I 5 4 4 . ,. 1'9I .
2218 28 23 13
t
6i 85 .. 6t 55 "
2 9 3 I
""
31 43 35 2I 20 22 34
3
?I --
190~.
Jan.
. .I
Feb. , ,t March., April ,,
May June July
August Sept. Oct. NOV. Dee.
, ..
89 85 89 82 72 72 7° 73 64
'39 37 37 46 5° 55 6t 58 59 8t. ~5I 88 42 9 4 ) 37 J
8 7 6
17
18 12 25 18 ti
~7
6
20 12 12 ,
6
I3
8
I7
4'I7
358
2"43. 3'99 3"00 I "84 I'64 6"02 "99 3"92 4'54 5"92
56 ! 29 55 .. 38'
.5 3 "3
11 2 3z 38
I
88 77
68
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m
Total Rainfall.
Number of wet days,
Clear
o
Rainfall.
Average Humidity,
Total
Numberer we~ d a y s .
Clear
Clouds
Temperature.
Average Humidity.
¢.n
I_-.9
t~
tz
PUBLIC HEALTH.
A N O T E ON T H E V A R Y I N G P R E V A L E N C E O F S C A R L E T F E V E R IN RELATION TO METEOROLOGICAL CONDITIONS. Bv A. L. DYKES, M.D. (Edin.), D.P.H. (Lond.), Assistant Medical Officer of Health, Oldham. is generally I T and waning
admitted that in the waxing prevalence of the infectious fevers there are factors at work which have not been defined, The problem here presented is of supreme importance in scarlet fever because of the great outlay of public money in its hospital isolatxon. Despite the fact that there are some seven hundred hospitals largely used for this purpose, the disease on the whole is as prevalent as ever in the community, In considering the failure of hospital isolation its function in controlling infection has to be clearly recognised. To be effective it must be the complement of efficient prevention outside. This has been proved in the case of smallpox. Where an outbreak has been energetically dealt with at the outset, all actual cases being removed at once and contacts vaccinated and kept under supervision, the spread of the disease has been arrested even in closely populated areas. So far as scarlet fever is concerned outbreaks can be similarly checked, but in urban areas it is commonly endemic while the removal of cases to hospital is continually going on. Evidently the " l e a k " in prevention is too large to patch up. A very probable explanation is that not only mild ambulant cases with little more than sore throat exist, but that carriers are also common : the infection of return eases by individuals who to all clin,.'cal tests are quite normal supports the latter suspicion. Another significant and practical point is that scarlet fever varies very greatly in infectivity, as is well shown by the diverse results of barrier nursing at different times. The infectivity of a fever, whether it be due to increased virulence of the micro-organism or to low resistance on the part of susceptibles, plainly bears on the feasibility of effective prevention. As regards changes in virulence little is known, but the theory that when a new strain of scarlet fever is introduced into a district the infectlon spreads more readily and tends to be more specially severe is not without supporting evidence. If it is true, then stringent measures are required to locate the original sources of infection in a given area.
293
Facts seeming to reveal the alternative condition, namely, a more or less general fall in resistance with consequent predisposition, may be m!sleading. Apparent predisposition may be in part or wholly a question of more effective and wider exposure. Thus, it may be true that there is an age-predisposition to typhoid fever among adolescents and young adults, but at the same time this period of life, especially with the working classes, is the one of greatest freedom. The age of close parental control is past, and such possible vehicles of the infection as shell-fish, watercress, ice-cream, milk, and water are likely to be obtained under doubtful conditions. Later, when many of these people have settled down in houses of their own, their chances of exposure to infection as an age group must be far less. As a parallel instance, in the South African W a r the young soldiers suffered especially from typhoid fever, but were less careful than their elders as to the source of drinking water and the need for steritising it. Much more will have to be done before it can be said, even in a general way, how far the prevalence of scarlet fever depends on acquired predisposition and extra exposure respectively. On the side of predisposition it may be said that no evidence has been elicited. It may be, however, that catarrhal rhinitis and sore throat opens the way to scarlatinal infection. An analogous process is observed in diphtheria, for patients suffering from scarlet fever are peculiarly liable to the faucial form of that disease, while as a complication or sequel of measles it usually assumes the laryngeal form. On the other hand, scarlet fever, unlike typhoid fever, ordinarily results from close association between donor and recipient, and the problem of extensive exposure in the community thus involves the mixing of susceptibles, particularly children. With these considerations in mind, I have examined the prevalence of scarlet fever in Oldham over a period of eleven years in relation to meteorological conditions. (See table). The average humidity, average temperature, average amount of sunlight, and total rainfall for each month of the eleven years I9O2-X2 inclusive are tabulated with the number of notified cases of scarlet fever and' resulting deaths. On first examining these tables no definite correlation was observed. In noting the relation of scarlet fever to rainfall it must be remembered that, in addition to differences in temperature, the cold months are accompanied by a higher humidity and fewer hours
of sunlight than the warm months, i have on this account roughly divided each year into two periods: the cold period containing the first three and last three months, and the warm period the remainder. Months have been classed as wet or dry according as the total rainfall yielded has been greater than five or less than two inches. Those with rainfall between these amounts have been excluded from the following table :-COLD
JUNE,
PUBLIC HEALTH.
294
PERIOD.
\¥ARM PERIOD.
~st three and last three months. Intermediate sir( months, N o . of wet m o n t h s .. 21 .. 18 Average n u m b e r of cases per wet m o n t h . . ., 51 -. 44 Percentage mortality . , 3"3% -, 5'5% N o . o f dry m o n t h s ., 9 -, I3 Average number of cases p e r dry m o n t h . . . . 36 ,, 41 Percentage mortality . . 2"3°[o . . I'8°/o
It will be seen that the average number of cases for a wet month exceeds the average for a dry month in both periods. The excess is marked in the cold period and comparatively slight in the warm period. This increased average in the veer months of the cold period may possibly be dependent to some extent on greater risk of exposure to infection and heightened susceptibility. During the cold months of the year if there is much rain, susceptibles are more liable to be brought into close contact both at school and at home. At this time of the year there are fewer holidays, and in wet weather the school children usually play in covered playgrounds ; also the humidity being high and the soil damp there is a greater liability to catarrhal conditions of the throat and upper air passages, and hence increased susceptibility to the scarlet fever virus. One would expect the case mortality to be higher than in the dry months for the same reason. In wet months of the w a r m period, on the other hand, it is conceivable that these causes do not operate to the same extent. Humidity is lower and the temperature being higher there is probably not the close association which is present in the colder months. It must be remembered also that the school holidaysare longer in the warm period. It is possible also that there are causes tending in this period slightly to increase susceptibility during dry months such as ineffectual flushing of sewers and increase of dust. These assumptions are rather strengthened by the fact that a wet month following a dry one during the cold period is frequently accompanied by an increase in the number of c.ases, while during the warm period this tendency is much less marked, a decrease being quite common.
Comparing the years of the series w i t h each other, the following facts will be noted :-(1) A succession of months: each with rainfall and humidity above the average may be accompanied by an increase in the number of cases (e.g., 19o5). (z) A very excessive rainfall if sustained may be accompanied and followed by a decrease of cases (e.g., 19o3). (3) A dry warm summer is frequently followed by a definite autumnal increase (e.g., 19o2, 19o 4 , 1911). In conclusion, my thanks are due to Dr. Wilkinson, medical officer of health of Oldham, who kindly allowed me to consult his annual reports, from which all necessary statistics were obtained. PREVALENCE
OF S C A R L E T ELEVEN
FEVER IN O L D H A M ¥'EARS.
FOR
Scarlet Fever~
1902. 25N
Cases. Dealh~
z ~
L--z_'
JF e ba. n,.. .899 2 4311 ~ l ! 5 7 March.. .. .. .. .. ~gAu~ust Sept. , ,
April May June Iulv
October Nov. Dec.
.,
89 75 72 72 69 73 75 80 85 96
43 45 47 55 58 56 55 5° 45 41
8 ~
I 2ol 7
8 7½ 8½ 8 8~ ~
15 18 2I 14 28 16 23
2"29 2'48 4"64 3"5 2"49 423 5 I1 2'52 7"35 2"5r
4'48'
233 5 ~ I 45 '27 4I 4I 60 80 62 1°3 94 93
I --4 2 3 5 1 5 9 6
1903.
9° 39 89 43 80" , 44 7° 43 74 5~ . 66 56 73 60, 79 57 75 55 85 5r 91 ~ 44 86 3~
Jail.
Feb.
March April
May
June July August Sept, Oct. Nov.
Dee.
~½ 6 6~ 5"
6 8 7 7½
12 18 23 15
3,51 .t 4"58 ~ 3'54 i 1"65 !
9
2"42 6"23 7'56 " 7 54 12"°7 I 5 4 4 . ,. 1'9I .
2218 28 23 13
t
6i 85 .. 6t 55 "
2 9 3 I
""
31 43 35 2I 20 22 34
3
?I --
190~.
Jan.
. .I
Feb. , ,t March., April ,,
May June July
August Sept. Oct. NOV. Dee.
, ..
89 85 89 82 72 72 7° 73 64
'39 37 37 46 5° 55 6t 58 59 8t. ~5I 88 42 9 4 ) 37 J
8 7 6
17
18 12 25 18 ti
~7
6
20 12 12 ,
6
I3
8
I7
4'I7
358
2"43. 3'99 3"00 I "84 I'64 6"02 "99 3"92 4'54 5"92
56 ! 29 55 .. 38'
.5 3 "3
11 2 3z 38
I
88 77
68
_
,
2
H ~. ~ - ~ .
.~tm
b5 ~
~ O 0 0 m todd-
::
::
O0~tm
O0
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:
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~:
.
:-
•
,
0
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tol~
~
Oared
~ -
=o"
Oa'~l ~ COOa O ' ~ o a ~ tO
& Oa,.6G ~ 6,
d~ -~ ~ r,.n ~ ~ Oatdt
. ~
0
d - . x d-, d , . d - ~
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CO Oatm ~
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Ce"-I Oat.n ~ D
: ' ~ "
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OOkO ~ ' - . I
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~1~
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=
Clouds =
o
m
Total Rainfall.
Number of wet days,
Clear
o
Rainfall.
Average Humidity,
Total
Numberer we~ d a y s .
Clear
Clouds
Temperature.
Average Humidity.
¢.n
I_-.9
t~
tz