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in the months of June and July and for England and Wales it was
during the months of August and September.
The picture portrayed by the table above, however, is rather
misleading for the following reasons :—
(a) The figures refer to uncorrected cases.
(b) The monthly figure is compiled by aggregating the
number of notifications received during any particular
month and this bears no relation to the actual dates of
infection.
It follows, therefore, that any inference drawn from these
figures regarding the prevalence of the disease in any particular
period of the year is faulty.
During investigations made in this Borough these additional
points have been noted :—
(1) Patients are often ' poorly ' some 4 or 5 days before the
Medical Practitioner becomes aware of the case.
(2) Patients are often admitted to hospital as ' suspected '
cases—notification being suspended until such time as
the case is confirmed.
(3) Confirmation of diagnosis may be a lengthy procedure,
often taking up to 14 days.
If the information gathered is to be of any value and if a really
true picture is to be obtained in respect of the incidence of Poliomyelitis,
it is apparent that some correction for these vagaries
becomes necessary. An ad hoc form was devised in order that
such amendments could be made to the Greenwich figures and
corrections have been made on the following basis :—
In all cases, whether notified before or after confirmation of
diagnosis, investigations were made to elicit the date when the
patient first became ' poorly
Then, assuming 14 days to be the average period of incubation
(current opinion is that the period is generally something
between 7 and 21 days), tho actual date of infection of each confirmed
case has been estimated to be two weeks prior to the
appearance of the first symptons.
This latter assumption, although not strictly accurate, is
sufficiently exact to enable certain inferences regarding infectious
periods to be made with some measure of success.