A set of training materials for professionals working in intervention epidemiology, public health microbiology and infection control and hospital hygiene.
You can't make decissions on this page's approval status because you have not the owner or an admin on this page's Group.
of outbreak types with examples:
Continuous common source
Intermittent repeated common source
Person to person transmission
Combination of the above
source followed by person to person transmission
- A common variation
- Implications for analytical
investigation (distinguishing early and late cases)
Early construction of epidemic curves, with
even imprecise information about cases, may prevent mistaken assumptions at the
outset regarding the outbreak source:
The graph below illustrates school absences
from a primary school in London during a particularly intense period of
norovirus (winter vomiting) activity in the wider community. Both school and
public health investigators initially attributed the outbreak to norovirus
infection. Somewhat later primary care doctors reported Salmonella infection in
a small number of the children affected.
Retrospective construction of an epidemic
curve, based on school absence records, suggested that the outbreak was in fact
arising from a point source, rather than a continuous environmental source
(norovirus activity in the community). (In this graph the occurrence of weekend
days (for which there are no school absence reports) should be noted, 23/24 and
30/31). It also suggested some (expected) secondary transmission of cases
within the school. Onset dates of the initial small number of known Salmonella
cases also coincided with this period.
A retrospective cohort analysis based on
school records for absences and whether children had meals at school or brought
packed lunches from home (no other analysi was considered feasible at this
point), showed that those who had the school lunch on the 21st or
22nd were 2.3 (95% CI 1.2 – 4.6) and 4.2(1.7- 10.4) times more
likely to have been absent from school in the subsequent week than children who
ate packed lunches on those dates.
Initial environmental officer review of the
school kitchens had been satisfactory, although there was no consideration of
the kitchen as a possible outbreak source at that time. If the epidemic curve
had been constructed at the outset, a different focus to the investigation
would have been followed, including a more intensive investigation of the
school kitchen, including microbiological sampling of environment, food and
possibly kitchen staff.
Figure: Epidemic curve of school absences,
and (later) confirmed Salmonella cases, in a primary school, London, winter
2010. Source: Health Protection Agency
You need to be logged in to post comments.
You can log in here. You can register here if you haven't done so yet.