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It may be seen from Table 3 that re-infection with
hæmolytic streptococci other than the primary type
occurred almost equally at all age-groups from 0—14
years. A decrease to 9 per cent. is seen in the 14 to 16year
old group. Among the thirty - five patients over
the age of 16 years, only two became re-infected during
their stay in hospital.
(e) The exact mode of spread of hæmolytic streptococci
in the scarlet fever wards was not ascertained, since
at the time of every re-infection there was among the
patients more than one possible source of the re-infecting
strain. In both Blocks A and B the majority of changes
of type occurred in small outbreaks, nine in all; of these,
five were limited to either a male or female side. Of the
remaining four outbreaks, which affected both male and
female wards, three were in Block A where the movements
of the convalescent patients were not restricted.
(f) The apparent failure of bed-isolation to control
the spread of hæmolytic streptococci in scarlet fever
wards has made it necessary to consider what further
factors may be of importance in this connection. Attention
has therefore been directed to the question of the
aerial spread of streptococci—by dust. Samples of dust
were collected from the ward floor, from the brooms used
and from the vacuum cleaner bag. In all cases large
numbers of haemolytic streptococci were isolated on blood
agar plates, counts varying from 20 colonies per plate to
several hundred being obtained from a few loopfuls of
dust. Random colonies picked for typing were of the
common scarlet fever types of haemolytic streptococci.
At the present time (May, 1939) we are in process of
testing whether a reduction in the incidence of change of
haemolytic streptococcal type will be effected by using
vacuum cleaning instead of sweeping as a means of cleansing
the bed-isolation wards.
By droplet nuclei: It has been found by Wells in
U.S.A. that fine droplets do not fall to the ground, but
that the surface moisture having dried off, infected