Invasive group A
s
treptococcal infection
has
a 15% case fatality rate
and
a risk of
secondary transmission.
This retrospective study
us
ed
two national data sources
from England
;
enhanced surveillance
(
2009)
and a case management system
(
2011
-
13)
to identify
clusters
of sever
e
group A streptococcal
disease
.
2
4
household
pairs
were identified.
The median
onset
interval
between cases was 2 days (range 0
-
28)
with simultaneous onset in
8
pairs
.
The attack rate during the 30 days after
first
exposure to a
primary
case was 4
52
0
per 100000 person
-
years at risk (95% CI
2
900
-
673
0
)
a
19
40
(
12
40
-
28
80
)
fold elevation over the background incidence
.
The
theoretical
number needed to treat (
NNT
)
to prevent one secondary case using
antibiotic prophylaxis
was 2
71
(
194
-
454
)
overall,
50
for
mother
-
neonate pairs
(
2
7
-
3
93
)
and
8
2
for couples
aged
75 years
and over
(
46
-
417
).
Whilst a dramatic
increased risk of infection was noted in all household contacts,
increased ris
k
was
greatest for mother
-
neonate
pairs
and couples
aged 75 and over
, suggesting
targeted
prophylaxis
c
ould be considered.
Offering prophylaxis is challenging due to
the
short
time interval between cases
emphasising the importance of immediate
notification
and assessment of contacts
.