London's Pulse: Medical Officer of Health reports 1848-1972
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Hints from the Health Department. Leaflet from the archive of the Society of Medical Officers of Health. Credit: Wellcome Collection, London
London County Council 1894
[Report of the Medical Officer of Health for London County Council]
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It has already been pointed out that the scarlet fever case mortality of 1894 was 5.2 per cent.
whereas in the preceding year it was 4.3 per cent.
The case mortality at "all ages" may be affected by more than one circumstance. There
was for instance, in 1893, a considerable prevalence of the disease at the end of the year, and hence
an excessive number of deaths was registered in the first two weeks of 1894, which even when dealing
with the large figures London supplies, naturally increases the apparent case mortality of 1894 when this
is calculated upon the number of cases notified and the number of deaths registered in that year.
Again the age and sex distribution of cases in a year is another factor which, it will be seen from the
preceding table, must needs affect the case mortality at " all ages." Thus, if the age distribution of the
cases in 1894 had been the same as in 1893, the case mortality at "all ages" cæteris paribus would
have been 4.9 instead of 5.28, and if further correction could be made for the number of deaths registered
in the first two weeks of 1894, among attacks notified in 1893, the case mortality at " all ages in
1894 would no doubt be still further reduced.
Beyond this is another modifying element which deserves to be taken into consideration. The
figures which are now supplied by the system of notification of infectious diseases in force in London
are sufficiently large to justify inquiry whether the case mortality of the disease is the same at all
periods of the year with a view to the elimination of influence, if any, of season.
For this purpose the following table has been prepared and the cases notified during 1894 have
been cast into months. The deaths have been dealt with in a similar manner, except that each
month's deaths begin a week later than each month's cases, so as to associate the deaths more closely
with the cases to which they belong. The approximate case mortality of each month can therefore
be seen—
Scarlet fever case mortalitxj, 1894.
| Month. | No. of weeks. | Cases. | Deaths. | Case mortality per cent. | Mean case mortality taken as 100. |
|---|---|---|---|---|---|
| January | 5 | 2,039 | 105 | 5.15 | 101 |
| February | 4 | 1,420 | 80 | 5.63 | 110 |
| March | 4 | 1,414 | 75 | 5.30 | 104 |
| April | 4 | 1,631 | 112 | 6.87 | 135 |
| May | 5 | 1,850 | 96 | 5.19 | 102 |
| June | 4 | 1,437 | 73 | 5.08 | 100 |
| July | 4 | 1,517 | 87 | 5.73 | 112 |
| August | 5 | 1,545 | 76 | 4.92 | 96 |
| September | 4 | 1,450 | 57 | 3.93 | 77 |
| October | 5 | 1,809 | 66 | 3.65 | 72 |
| November | 4 | 1,278 | 59 | 4.62 | 91 |
| December | 4 | 1,050 | 55 | 5.24 | 103 |
The above table shows that the case mortality of this year was above the mean at the beginning
and end of the year, and below the mean in the late summer and early autumn months.
With a view to obtaining more trustworthy results a similar table has been prepared based on
the cases and deaths occurring in the years 1891-94.
Scarlet fever case mortality, 1891-94.
| Month. | Cases. | Deaths. | Case mortality per cent. | Mean case mortality taken as 100. |
|---|---|---|---|---|
| January | 5,470 | 339 | 6.20 | 136 |
| February | 4,568 | 259 | 5.67 | 124 |
| March | 5,051 | 285 | 5.64 | 123 |
| April | 5,682 | 317 | 5.58 | 122 |
| May | 7,107 | 321 | 4.52 | 99 |
| June | 7,833 | 374 | 4.77 | 104 |
| July | 8,849 | 379 | 4.28 | 94 |
| August | 9,698 | 436 | 4.50 | 98 |
| September | 11,032 | 380 | 3.44 | 75 |
| October | 11,590 | 385 | 3.32 | 73 |
| November | 10,630 | 449 | 4.22 | 92 |
| December | 6,322 | 366 | 5.79 | 127 |
This table exhibits a decided tendency of the case mortality to be at its maximum at the
beginning of the year, to fall to a minimum in September and October, and then to increase in
successive months until the maximum is again reached. This " seasonal " variation in case mortality
is matter of considerable interest, and not least for the reason that the months of greatest prevalence of
disease are not the months of greatest case mortality.
In view of what has been shown as to the effect on the case mortality at "all ages " of the season
of the year, it is necessary to determine whether this seasonal variation may not be itself dependent on
differences in the age and sex distribution of the cases notified.